Lit Links

So, in case any were wondering, my area on the East Coast was mostly spared the wrath of Hurricane to Post-Tropical Cyclone Sandy.  Some rain, a bit more wind, but not many power outages in the immediate area.  I am however fairly well prepared for any mystery zombie apocalypses that might arise (from the dead).  I hope that all of you reading who were subject to its furor endured the storm as well as possible.

In any case, some bits of possible interest -

1.) PNAS has a special feature this week on "the Chemical Physics of Protein Folding."  Sadly, it's behind a paywall for the time being.

1.5.) Related to this, I once mentioned a while back in a comment (I believe over at the Inquisitive Ket) about one of the less-important reasons Levinthal's paradox never really bothered me, namely, that proteins aren't really free to sample all possible conformations due to their interactions with other proteins (even indirectly due to crowding), the solvent, and with itself.  In any case, it's always interesting to see people carefully examine these sorts of questions in the recent literature.  

2.) Gaining structural insight occasionally takes a while.  It also reminds me of the utility of neutron science for biochemistry - the ability to use contrast variation using selective deuteration make it possible to probe multicomponent systems.  And let's not forget that one can also use neutrons for spectroscopic measurements. 

Anyway, back to the actual science…..  Read more!

Quantum biology - A Rose By Any Other Name?

I believe I may have off-handedly mentioned some of this work somewhere in a blog comment semi-recently, but I suppose some further thoughts would not be out of place at this time.  I bring it up because of this preprint and this article about said preprint.

Clearly, on one level, quantum mechanics - via chemistry - underlies biology.  This is, I suspect, a fairly unoffensive statement.  Chemical reactions are quantitatively studied in a quantum mechanical framework, and I don't see biochemical reactions being much different. 

On another level, direct appeal to quantum mechanical behavior to explain biology can seem kind of silly.  Biology is slow, wet, messy, and takes place at a whole bunch of time and length scales.  I imagine many of us recall the exercise - likely done in an introductory general chemistry course, at least in my experience - where one calculates the de Broglie wavelength for an electron and then, say, a baseball. 

Of course, when one looks at table 1 in the preprint, a light goes on.  Long-range electron transfer in proteins?  The role of tunneling in enzyme catalysis?  Vision - which involves the photochemistry of a protein-immobilized chromophore?  Photosynthesis?  A proposed radical spin mechanism for avian magnetoreception? 

This all reeks of physical(ly predisposed) chemists trying to get their dirty mitts onto a whole lot of funding.  Not that there's anything wrong with that, mind you - I'm presently trying to work "quantum biology" into my CV/resume as we speak. 

But for sake of argument, let's take a look at the Fenna-Matthews-Olsen (FMO) protein from a green sulfur bacterium where quantum effects were observed via 2D electronic spectroscopy.

Yep, definitely a protein.  But what's all of that inside the protein?

Why, it looks like the protein is the wrapping for a photochemically delicious filling of chlorophyll molecules!  I could envision that this is the sort of environment which would be conducive for maintaining some sort of quantum mechanical excitation. 

But what about - for instance - microtubules, which some have suggested play a role in consciousness via quantum mechanical effects?  Why, there's even GTP (GDP) known to associate with tubulin in the structure!  Let's take a look -

Hmmm.  Let's focus on the GTP and GDP, so how about….

Well, that was kind of anticlimactic.  That's it?  That is somehow supposed to sustain and nurture our very consciousness from the harsh decoherent world out there?  I find myself skeptical. 

I suppose that is as good a place to end as any.  I may or may not have more to say in the future after I've had a chance to properly consume and digest the preprint.  While I do find the idea of nature exploiting exciton transport, radical spin pair chemistry, proton tunneling, and so on incredibly exciting - I don't think taking that and wantonly speculating is the best route.   

FYI - This was also mostly a chance to play around some more with UCSF Chimera.  Just started using it a bit earlier this year, so if anyone has any tips or list of useful tricks, please share!  The structures were generated with this program using PDB ID 3ENI (FMO protein) and 1JFF (tubulin).  Read more!

Lit Post.

A few interesting-looking papers that I have stumbled across lately:

- Cellular solid-state nuclear magnetic resonance spectroscopy. Clearly, analyzing membrane proteins that are still in the native intact cell membrane is what we'd all like to see.

- Red wine, iron telluride, and superconductivity. Sadly, I do not think that soaking any of my biological samples in a preferred alcoholic beverage will facilitate noteworthy results. Although perhaps I should try, just in case.....

- The Next Big(ger) Thing. Actually not a research article, it's a news item on mesoscale science.

As I've had to suppress a fair amount of sarcasm while writing this post, I will end things here. Read more!

You Shall Pass!

I saw this paper, and it was just asking be blogged about here. I figured I’d give it a shot.

Disclaimer – Not my work, never met any of the authors (although I’m sure they’re all within six degrees of me scientifically). The paper is open access, which I think is a good policy for me to adhere to in any future efforts along these lines.

Citation: L.A. Clifton, et al. “Low Resolution Structure and Dynamics of a Colicin-Receptor Complex Determined by Neutron Scattering.” The Journal of Biological Chemistry. Vol. 287, No. 1, pp. 337-346; January 2, 2012.

Among the many things that bacteria can do, one of them is knocking off other bacteria. There are a number of ways to go about this critical task, not surprisingly, and one of them involves proteins known as bacteriocins. These are proteins that the bacterium uses to kill off potential competitors, as they typically go after closely related bacteria. In this paper, the authors are focusing on Colicin N (ColN), a bacteriocin produced by E. coli. ColN depolarizes the inner membrane of Gram-negative bacteria by forming pores in the inner membrane, resulting in cell death.

The question the authors address is a fundamental one – how does ColN get past the lipopolysaccarhide-decorated outer membrane of a bacterium? It is ~ 40 kDa in size - so, clearly, not going to be able to easily masquerade as an ion or small molecule and pass unhindered through a pore in the outer membrane. The authors note that past research on ColN demonstrated that it is dependent on the presence of an outer membrane protein, OmpF (or related porins), to be effective. Cells that are OmpF-deficient will not be killed off by ColN. I should note that OmpF is a trimeric porin that permits the passage of ions and small molecules through the outer membrane. It was suggested that ColN could pass through the OmpF pore, but would need to be completely unfolded to do so. So there is clearly something going on here that is interesting.

The paper describes a multipronged approach to this question – the authors integrate microscopy, neutron reflectivity, and small angle neutron scattering (SANS). The authors step through their case – they first present the thin film imaging (Brewster’s angle microscopy) and neutron reflection data for their model of the OmpF/phospholipid monolayer. The microscopy suggests similar stability for the OmpF/phospholipid monolayer, although different topography and compression behavior (the formation of domains appears less evenly distributed in the OmpF/phospholipid monolayer, and there are “kinks” in the isotherm for the phospholipid-only monolayer compared to the OmpF-containing one). The neutron reflection data also seems to support the existence of an OmpF/phospholipid bilayer, despite Fig. 3B being mislabeled by my eye. Normally the neutron “refractive index” - neutron scattering length density, aka nSLD – is plotted as a distance away from some reference (e.g., an easily determined interface or a metal layer on which your sample is ultimately deposited). It seems that is what they intended to write (the x-axis seems to be labeled as such) but is mislabeled with the “Q/A^-1” tag.

In any case, much of biologically-oriented neutron scattering is dependent on the existence of contrast variation in the nSLD. You can purchase deuterated compounds (such as lipids), prepare buffers in deuterium oxide, and even express & purify deuterated proteins. You then mix and match your deuterated and protonated components to see what each component looks like when in complex with everything else. It is a low-resolution means of doing so, but the benefits can outweigh the disadvantages.

The authors move onto the ColN portion of their work, showing the microscopy and neutron reflection data for ColN interacting with the OmpF/lipid monolayer. The time-lapse microscopy of ColN with the pure lipid monolayer and the OmpF/lipid monolayer shows increased image intensity, but appears to “smear” homogeneously with the pure lipid monolayer while forming larger, brighter spots with the OmpF/lipid monolayer. Their analysis of the neutron reflectivity data indicates the presence of the ColN in the same layer with the OmpF, and not just interacting with its surface, as they see in the ColN + pure lipid monolayer sample. Given the contrast variation matching, they state that they are able to see ColN extend as it inserts into the lipid region, suggesting that it is unfolding to some extent. The increase in surface pressure would suggest that it is not going through the OmpF pore but is, instead, inserting into the lipid region next to the OmpF. If it was inserting through the pore channel, the surface pressure might be expected to level off and not keep increasing.

The SANS data round out the story – they’re looking at the ColN/OmpF complex in detergent. (I know, I know.) Anyway, their data-derived model has one of the ColN domains slithering down between the cleft between OmpF monomers, while the remainder of ColN remains protruding outward. If you look at Fig. 6C, the blue distance distribution (where you are only looking at scattering from ColN) has two peaks, one that overlaps with the red trace (where one is only looking at OmpF) and a separate peak. So this at least makes sense. They do discuss the potential for translocation via the pore, and some recent literature on that possibility.

Mostly, I thought that this was a really interesting bit of research – while there is the obligatory mention of potential application to antibiotic development, it’s pretty obvious that the fundamental scientific question of “how does a largish protein get across a cell membrane where the cell has no interest in letting it inside?” I think that the experiments were reasonable, were carefully done, and did not set off too many massive alarms in my brain while reading. I would like to think that you could use something like nanodiscs or bicelles for the SANS studies so you could at least approximate a native membrane environment – clearly, sample homogeneity is a concern, as scattering methods can be notoriously sensitive. (Did I ever tell you about the time I spent a good afternoon into evening washing banjo cells for SANS experiments since said cells were just disgusting?) I haven’t worked with nanodiscs – although I’ve heard and read more than I can shake a stick at - and my experience with bicelles hasn’t been quite so detail-oriented, so maybe it would require sublime experimental mastery beyond the typical.*

Anyway. That was kind of fun. Also, how many of you saw Ohm’s Law Survives to the Atomic Scale? I imagine people will want to confirm this, as it is definitely seems really cool. Clearly, it was custom-made by “hand” (well, scanning tunneling microscope), so no immediate applications to large-scale mass production any week soon, but that isn’t why we do science.

Now, off to think about thermodynamics for a while. I need to come up with a reasonable explanation of some data today….. Read more!

Surely you jest!

So, I strongly recommend everyone checks out this paper -

Accessing protein conformational ensembles using room-temperature X-ray crystallography

- which was just published in PNAS this week. The paper cites a 2004 paper by Bertil Halle (which I mentioned a while back) on the potential consequences of flash freezing and cryocrystallography.

Enjoy! Read more!

No, I am not going to talk about the recent paper on the success of Foldit. Mostly since if you can even get a crystal structure for something, it's probably not agonizingly painful enough for me to work on - as I've said before, give me your disordered, your poorly soluble, your aggregated masses yearning to be analyzed.

Anyway, I wanted to mention this interesting-looking paper:

Binding Leverage as a Molecular Basis for Allosteric Regulation. I haven't had a chance to really dig into the paper, but the idea itself is simple enough - ligand binding can couple to various collective motions in proteins to varying extents, due to which we observe allosteric modulation of enzyme function. There are obvious oversights (one example that they mention in the paper - the lack of attention paid to proteins that aren't enzymes such as signaling proteins of various types), and I'd want to pore through which structures they used in the PDB (e.g., how did they deal with the family of structures that are generated by NMR if applicable). Then again, I usually consider thought-provoking ideas worth the publication, even if a judiciously skeptical outlook may make them seem a little less lustrous. Read more!

A few quick thoughts.

I am still trying to unenviably navigate an n-dimensional parameter space, attempting to optimize the biochemistry for the present bane of my existence in order to get to some proper structural & biophysical studies. It is further complicated that whenever I do seem to devise a plan, something odd crops up in my data in amidst the general experimental madness (remember, if you work with n components, you need to vary one and keep n-1 constant : easier said than done!).

In any case, I stumbled across this interesting paper. Given my innate worrying about structural data obtained under cryogenic conditions, this was right up my alley – utilizing mesoporous materials to confine proteins and their hydration waters, and then using your interrogation method of choice across a range of temperatures without having to worry about the effects of bulk water. I can envision that this would be an excellent way to more explicitly bridge the gap between cryocrystallography and dynamic/functional studies done under more physiologically relevant conditions.

There was a very long back-and-forth over at The Curious Wavefunction this past week. I basically have the opinion that expecting physics to “explain” chemistry and biology is perhaps a bit overly demanding. I mean, it’s not as if all physicists are just waiting to wrap up high-energy/elementary particle physics and then retire, after all! There are still a number of unresolved questions in physics, and as a number of them involve many-body systems, it would only seem reasonable that those are the ones that would likely be of the most immediate application to chemistry and biology.

Now to finish preparing for this inclement weather…..
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As has been often noted about a number of topics, one’s biases will always skew one’s perspective.

On the one hand, we have this very interesting paper where the authors suggest correlated motions in ubiquitin over a distance of ~ 15 Angstroms (1.5 nm) based on further squeezing information from previously acquired NMR data with the help of computational methods. On the other hand, there is this other very intriguing paper where the authors put forth using gadolinium tags as a way to obtain structural constraints in proteins on the order of ~ 6 nm (60 Angstroms) via ESR/EPR techniques.

In the former, we’re looking at proposed long-distance correlations based on a bunch of relatively weak, short-range interactions (NOEs and RDCs), while in the latter we have nanometer-scale distance constraints being derived from a technique that is well matched to determining distances at the nanoscale. I figure the astute reader can figure where I stand on each given my tone.

Suffice it to say, it’s the reason why I’ve recently developed an interest in ¹⁹F NMR (oh, to work with a nucleus that has a decent gyromagnetic ratio and isn’t as common as protons in biological materials!), for one, as well as metal binding tags for paramagnetic relaxation enhancement studies.

In other news, my resolution for the second half of 2011 is to always try and work in a mention of the Helmholtz free energy into each discussion I am involved in that touches upon thermodynamics, as I think far too many chemists have gotten comfortable in their Gibbsian-oriented world.

I suppose this is one of those “it was bound to happen” things – one of the summer undergraduates who is in my lab at my current institution mentioned that the undergrad biochem lab uses a hexahistidine-tagged protein for overexpression & purification. I of course remember having to prep and subsequently grind up giant amounts of animal muscle to extract a protein in my undergrad biochem lab. I feel slightly dusty.

With that observation, I will call this blog post to an end. Read more!

SAXS And Promiscuity - Or, What Your Biochemistry Text Doesn't Cover.

Glycolysis is one of those things you learn about as an undergraduate (in high school as well, to be fair, but in a good bit more detail in an undergraduate biochemistry course) and – at least in my experience – it was presented as a topic that had already been well-explored and thoroughly annotated. After all, if it hadn’t been, would they have put it down for posterity in a textbook?

Snickering aside, I was pretty intrigued to see the following paper the other day for more than just being another entry in my “clearly, plenty of mechanistic detail was glossed over in my biochem text” list. Basically, the research team utilized a combination of crystallography, small-angle x-ray scattering (SAXS), and computational model to develop a scheme for the mechanism of phosphoglycerate kinase. They propose that the enzyme has a preferred “open” conformation where substrates (1,3-bisphosphoglycerate and ADP) can bind (separated by over 15 angstroms), and then a “closed” conformation, where the domains “fold in” on one another, bringing the substrates together for chemistry and which exposes a hydrophobic patch, which they suggest drives the preference for the “open” conformation. In the supplemental info, they do have some movies for download which make for fun viewing.

It is a nice example of what some in the structural biology field have been pulling for, an integration of high-resolution methods with lower-resolution methods that can provide additional insight into dynamics at the domain scale and above. Just as a representative example of this thinking is the SIBYLS beamline at Lawrence Berkeley Lab (SIBYLS – Structurally Integrated Biology for Life Sciences, where they possess the ability to do both crystallography and SAXS at the same station). They’ve also got a fairly lengthy review linked to on that page that describes the interplay between crystallography, SAXS, and computational methods.

In the spirit of Wavefunction’s link post the other week, at least, I stumbled across this recent paper on stochastic ensembles, conformationally adaptive teamwork, and enzymatic detoxification today. I am still working through the paper, but – given that one of the authors has written rather extensively on atypical (non-Michaelis-Menten) kinetics in enzymes – he is putting forth a new set of organizing thoughts for understanding the unusual substrate binding and catalytic properties of detoxification enzymes (which frequently have multiple isoforms differentially expressed in tissues). These enzymes are not only promiscuous in terms of the substrates they’ll work with, but are also involved in multiple metabolic processes. So it's hardly as straightforward as biochem texts are fond of portraying with those nice, neat flow charts. I have occasionally considered this as a possible reason for all those secondary metabolites in plants that no one can figure out why they're present in the first place - you have a bunch of enzymes floating around in the cells and given enough time, stuff happens. But that is perhaps another post for another day. Read more!

Some random thoughts....

Or, Structures, Struggles, and Teaching People How to Make Nuclei Dance.

So, a few issues of interest and/or importance to yours truly. This is going to be short.


1.) Vaults! I've suddenly become very entranced with both their structural (39-fold dihedral symmetry for the win!) and functional (no one really knows what they do!) beauty. The structure of rat liver vault at 3.5 Angstroms was recently published (see here) – they were able to clearly assign the major vault protein (MVP) to the electron density, while the other proteins and ribonucleic acid is still up in the air. The internal dimensions of approximately 620 Angstroms in length and 400 Angstroms in diameter is enough to encapsulate most entities within the cell. There's some mention that they might interact with lipid rafts, given some sequence homology considerations. Amusingly, since the number of coordinates and structure factors exceeded what could be put in a PDB file, it's been deposited under three separate accession codes.

2.) I mentioned not too long ago that I'm having some issues with our resident BIAcore (surface plasmon resonance) system. Let me describe to you a representative issue with the current chip and setup: The baseline for the control surface after being coated with buffer and blocking agent is significantly lower than the original baseline. It is possible we have a bad chip, or a bad instrument (some sort of drift in the optical components), or something else. So while troubleshooting and such is going on, it brings to mind a major difference between my current work and former work in terms of nature and aspect. With the SPR setup, it's a unit that is, for lack of a better phrase, a single entity. Sure, we can remove and insert sensor chips, and it's controlled by the adjacent computer, but it's basically a large self-contained box. I can't really go peeking inside, checking things out for myself since it's a shared facility instrument. Back when I was boldly going where no one had gone before in the world of NMR, it was all modular and accessible. I had a oscilloscope checking on the forward and reverse power going to and coming from the probe (remember, in ssNMR, one works with higher RF powers than in solution, typically), I could break out the network analyzer to check the performance of the probe or an amplifier/frequency generator, I could open up the probe to see what chaos might have befallen us, I could always quickly toss in a standard sample (adamantane, KBr, glycine) to quickly assess how far off-course we might have strayed.... I could change filters/attenuators in an appropriate fashion to see where misery was striking at the heart of my experiment. And there was a sense of general, simple assessibility – I could use any network analyzer that I could borrow from someone in the department to check what I might see with my lab's. I could always repack a chemical standard with new material from scratch without it being a big deal or expenditure of time. I could examine the raw data to check and see if the FID was starting at a maximum or minimum (there's a way to check the angle in the SPR software, but it doesn't seem to be something most people do), for instance.

I suppose it's a matter of personal experience – my graduate experience was analogous to the laboratory where I worked as an undergraduate (where we did primarily EPR and time-resolved optical spectroscopy). I – as a general rule of thumb – like to know what's going on at a certain foundational level. I am not a fan of being told, “Yeah, you need to call the company and ask.” I expect with time I will get more used to such commercially available instrumental setups, but until then, I shall lament this state of affairs.

3.) I have a wild bug up my nose about the issue of how to best teach NMR to people. I think most people familiar with magnetic resonance first become acquainted with it via the module in introductory organic chemistry classes, with maybe a mention of it in the introductory physics sequence. Now, I don't really think that there's anything wrong with this – when I was taking organic chemistry, I had the inspired thought, “Hey, protons are spin-1/2 particles, but so are electrons....what about coupling those spin-1/2 particles with nuclei that are spin-1/2 particles? Could we correlate nuclei to electrons? This could be useful for metal-containing systems, since you've got unpaired electrons!” I did some math, and then I found out who George Feher was, and then my moment of insight became bittersweet. I had a few extra drinks that weekend to get over the disappointment, and now that I've told my “how I independently rediscovered ENDOR” story, I won't be tempted to tell it again for a while. However, back to the question - what about the next step? It seems that most people get a “structural determination via spectroscopic/physical methods” sort of class, where they also get into additional methods such as IR, UV/Vis, mass spec, and the like. But, let's say that I become science czar, and I mandate that NMR be removed from this class and be included in a one semester (or equivalent) course in NMR. What else should we teach in this course? How broadband should its audience be – should we let biochemists who have a thing for structural biology expect to get something out of it as well? What about physics majors who are plotting on becoming chemical/molecular physicists and possibly develop the next generation of NMR experiments and applications? How much “death by operator algebra” should we have in this class? What kinds of experiments should be include in the lab component? I have my own ill-formed opinions at this point in time, but it's been fun to mull over on my own and I thought I should share.


And just like that, I'm gone....

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It's Cold In Here

Or, One More Reason to Take Protein-Ligand Crystal Structures with A Grain of Salt


This is going to be a really short post. Sorry, folks.

Ashutosh pointed out the other week to be wary of ligands in the Protein Data Bank (PDB) – see here. This is of course good advice, and everyone should read that post on the off chance they haven't already done so. Done? Good!


One other thing that I think is underappreciated by those who aren't protein crystallographers/structural biologists/biophysical BAMFs is that, for the most part, modern (synchrotron) protein crystallography is done under cryogenic conditions. Now, this typically is a bit warmer than the boiling point of liquid nitrogen, so you've got a protein crystal wallowing around somewhere above 90 K but not too far above 150 K. I'm not going to say that this is an entirely bad thing – it minimizes radiation damage, allowing for the higher-flux radiation sources to do their job. This of course can lead to higher-resolution structures and most of us generally appreciate that. However, here's the question – does it accurately represent the protein-ligand complex under physiological conditions?

A really interesting analysis of this question was addressed a few years back in 2004 by Bertil Halle from Lund University. I would recommend reading the paper, but if you're interested in the abbreviated conclusions, to wit:

1.)Flash-cooling of protein crystals – and subsequent cryocrystallography – is capable of retaining the general backbone fold and positioning of the protein, but

2.)The quenching of the solvent/ligand/ion degrees of freedom are not necessarily an accurate representation of the complex under physiological conditions and are probably more indicative of the system at the glass transition.

So the next time you look at a crystal structure and wonder, “How in Hades did that ligand end up there?” think about this. For a macroscopic analogy, consider the following structure:



Now, if it were 50 degrees colder, while the overall positioning would be similar, there's no reason to expect that every finger, strand of hair, and toe would be in the same position.

Expect more thoughtful posting one of these days, but don't hold your breath....

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Clusters of Spins (AKA the Promised NMR Lit Post)

So, here's the citation-heavy post about some interesting work done on systems of primarily – but not exclusively – biological interest via magnetic resonance spectroscopy since the turn of the century (I've always wanted to say that).


I mentioned CERM at the University of Florence in my last post for good reason – it's something of a place where, sooner or later, all paths seem to cross there in one way or another. It's either having read one of the texts that's come out of the faculty there, collaboration, or you just find inspiration in what they're doing. Because I have a certain unavoidable bias towards ssNMR out of (most likely) residual Stockholm Syndrome, I will mention this paper as an example of extending the work done at Florence in using NMR to understand paramagnetic metalloproteins in solution to the solid state.

Lyndon Emsley and coworkers at ENS-Lyon are pursuing a number of really interesting projects in magnetic resonance, both of basic importance to NMR (see, for instance, this paper) as well as to problems in chemistry, metabonomics, biology, and paramagnetic systems.

Paul Ellis & coworkers at PNNL have done some really stunning work with Zn-67 ssNMR and Mg-25 ssNMR. Zinc is one of the most common metal cofactors found in biology, and they've managed to do direct measurements of zinc in proteins via solid state NMR (see here and here for examples). Given that it's a quadrupolar nucleus, it's even more awesome. (While comments noting that they do this sort of work at really low temperature are accurate, it does not diminish its luster.) Magnesium-25 is another nucleus that this group has focused on as of late. See this paper for some Mg-25 ssNMR. The applications to half-integer quadrupolar nuclei in general, as well as their efforts in developing low-temperature ssNMR methods, are of interest in general and not just for biological systems.

Dieter Suter and his group at Dortmund have done some really neat things with optically-detected magnetic resonance, including metalloprotein research and their work on NMR of quantum wells. You can read more at their webpage here Fortunately for all of us, you can find a number of publications here. Suter was also involved in the Pines' group work on geometric phases in the late 1980s, so if you love it when interesting theory and experiment comes together, it should bring a smile to your face.

The Jaroniec group at Ohio State has been doing a variety of interesting things in solid state NMR, but I will mention their work with spin-labeled proteins here since it most tickles my fancy. You can read about it here, where they used spin-labeled proteins to obtain long-range structural constraints. Another advantage of spin-labeling is in facilitating assignment of congested NMR spectra – since you know where you introduce your spin label, you could potentially “blank out” certain residues that crop up in these congested regions to simplify assignments.

This is by no means a comprehensive list or thorough assessment of the field, more just intended to whet one's appetite. I would also like to point out the lecture notes from a solid state NMR workshop for graduate students and postdocs here. It may be a bit much to take in all at once, but some of you may find it makes for interesting reading despite not having a chance to hear the actual lecture. (FYI – no, I did not attend this workshop.) The list of speakers is a lineup of some of the major players in (biological) solid state NMR in the United States. If one's curiosity is still rampant, and you wish to expand your geographical purview, here is a list of lecture notes from a European ssNMR school (which, in case you're trying to pin me down, I did not attend) taught by a number of the major names in ssNMR in Europe. While I've long since downloaded these files and saved them, I can't guarantee that all lecture notes are still functional.

FYI - If I didn't mention you or your advisor or past advisor, I really didn't mean to do so. I would be pretty sure you've done/are doing awesome work, it's just that this is not a detailed journal club-style post. I will take recommendations, though, for any possible "journal club"-style posts, where the focus is on a single article or group of related articles. Tell me what totally BAMF science you've done, I'd love to hear it!
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