http://chekhov.cs.vt.edu/PAPERS/Plaxco.pdf

Contact order, transition state placement and the refolding rates of single domain proteins

Topological and energetic factors: what determines the structural details of the transition state ensemble and "en-route" intermediates for protein folding? An investigation for small globular proteins

The “protein folding problem” consists of three closely related puzzles: (a) What is the folding code? (b) What is the folding mechanism? (c) Can we predict the native structure of a protein from its amino acid sequence? Once regarded as a grand challenge, protein folding has seen great progress in recent years. Now, foldable proteins and nonbiological polymers are being designed routinely and moving toward successful applications. The structures of small proteins are now often well predicted by computer methods. And, there is now a testable explanation for how a protein can fold so quickly: A protein solves its large global optimization problem as a series of smaller local optimization problems, growing and assembling the native structure from peptide fragments, local structures first.

/pdf/the-protein-folding-problem-je8tdyrxrg.pdf

The Protein Folding Problem

http://www-jackson.ch.cam.ac.uk/publications/1998/1998_FoldDes.pdf

How do small single-domain proteins fold?

The polypeptide chains that make up proteins have thousands of atoms and hence millions of possible inter-atomic interactions. It might be supposed that the resulting complexity would make prediction of protein structure and protein-folding mechanisms nearly impossible. But the fundamental physics underlying folding may be much simpler than this complexity would lead us to expect: folding rates and mechanisms appear to be largely determined by the topology of the native (folded) state, and new methods have shown great promise in predicting protein-folding mechanisms and the three-dimensional structures of proteins.

A surprising simplicity to protein folding

The kinetics of folding of a tryptophan containing mutant of the IgG binding domain of protein L were characterized using stopped-flow circular dichroism, stopped-flow fluorescence, and HD exchange coupled with high-resolution mass spectrometry. Both the thermodynamics and kinetics of folding fit well to a simple two-state model:  (1) Guanidine induced equilibrium denaturation transitions measured by fluorescence and circular dichroism were virtually superimposable. (2) The kinetics of folding/unfolding were single exponential under all conditions examined, and the rate constants obtained using all probes were similar. (3) Mass spectra from pulsed HD exchange refolding experiments showed that a species with very little protection from exchange is converted to a fully protected species (the native state) at a rate very similar to that of the overall change in tryptophan fluorescence; no intervening partially protected species were observed. (4) Rate constants (in H2O) and m values for folding and unfolding...

Kinetics of folding of the IgG binding domain of peptostreptoccocal protein L

The thermodynamic stabilities of small protein domains are clearly subject to natural selection, but it is less clear whether the rapid folding rates typically observed for such proteins are consequences of direct evolutionary optimization or reflect intrinsic physical properties of the polypeptide chain. This issue can be investigated by comparing the folding rates of laboratory-generated protein sequences to those of naturally occurring sequences provided that the method by which the sequences are generated has no kinetic bias. Herein we report the folding thermodynamics and kinetics of 12 heavily mutated variants of the small IgG binding domain of protein L retrieved from high-complexity combinatorial libraries by using a phage-display selection for proper folding that does not discriminate between rapidly and slowly folding proteins. Although the stabilities of all variants were decreased, many of the variants fold faster than wild type. Taken together with similar results for the src homology 3 domain, this observation suggests that the sequences of small proteins have not been extensively optimized for rapid folding; instead, rapid folding appears to be a consequence of selection for stability.

https://www.pnas.org/content/pnas/95/9/4982.full.pdf

The sequences of small proteins are not extensively optimized for rapid folding by natural selection

Contrasting roles for symmetrically disposed β-turns in the folding of a small protein

We use both combinatorial and site-directed mutagenesis to explore the consequences of surface hydrophobic substitutions for the folding of two small single domain proteins, the src SH3 domain, and the IgG binding domain of Peptostreptococcal protein L. We find that in almost every case, destabilizing surface hydrophobic substitutions have much larger effects on the rate of unfolding than on the rate of folding, suggesting that nonnative hydrophobic interactions do not significantly interfere with the rate of core assembly.

/pdf/robustness-of-protein-folding-kinetics-to-surface-3sado21iq5.pdf

Hongdi Gu

Papers

Kinetics of folding of the IgG binding domain of peptostreptoccocal protein L

The sequences of small proteins are not extensively optimized for rapid folding by natural selection

Contrasting roles for symmetrically disposed β-turns in the folding of a small protein

Robustness of protein folding kinetics to surface hydrophobic substitutions