Protein folding

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"Protein thermodynamics" redirects here. For the thermodynamics of reactions catalyzed by proteins, see Enzyme.
Protein before and after folding.
Results of protein folding.

Protein folding is the physical process by which a protein chain acquires its native 3-dimensional structure, a conformation that is usually biologically functional, in an expeditious and reproducible manner. It is the physical process by which a polypeptide folds into its characteristic and functional three-dimensional structure from random coil.[1] Each protein exists as an unfolded polypeptide or random coil when translated from a sequence of mRNA to a linear chain of amino acids. This polypeptide lacks any stable (long-lasting) three-dimensional structure (the left hand side of the first figure). As the polypeptide chain is being synthesized by the ribosome, the linear chain begins to fold into its three dimensional structure. Folding occurs even if it has not yet finished translating the entire polypeptide chain. Amino acids interact with each other to produce a well-defined three-dimensional structure, the folded protein (the right hand side of the figure), known as the native state. The resulting three-dimensional structure is determined by the amino acid sequence (Anfinsen's dogma).[2] Experiments [3] beginning in the 1980s indicate the codon for an amino acid can also influence protein structure.

The correct three-dimensional structure is essential to function, although some parts of functional proteins may remain unfolded,[4] so that protein dynamics is important. Failure to fold into native structure generally produces inactive proteins, but in some instances misfolded proteins have modified or toxic functionality. Several neurodegenerative and other diseases are believed to result from the accumulation of amyloid fibrils formed by misfolded proteins.[5] Many allergies are caused by incorrect folding of some proteins, because the immune system does not produce antibodies for certain protein structures.[6]

Known facts[edit]

Relationship between folding and amino acid sequence[edit]

Illustration of the main driving force behind protein structure formation. In the compact fold (to the right), the hydrophobic amino acids (shown as black spheres) are in general shielded from the solvent.

The amino-acid sequence of a protein determines its native conformation.[7] A protein molecule folds spontaneously during or after biosynthesis. While these macromolecules may be regarded as "folding themselves", the process also depends on the solvent (water or lipid bilayer),[8] the concentration of salts, the pH, the temperature, the possible presence of cofactors and of molecular chaperones.

Minimizing the number of hydrophobic side-chains exposed to water is an important driving force behind the folding process.[9] Formation of intramolecular hydrogen bonds provides another important contribution to protein stability.[10] The strength of hydrogen bonds depends on their environment, thus H-bonds enveloped in a hydrophobic core contribute more than H-bonds exposed to the aqueous environment to the stability of the native state.[11]

The process of folding often begins co-translationally, so that the N-terminus of the protein begins to fold while the C-terminal portion of the protein is still being synthesized by the ribosome. Specialized proteins called chaperones assist in the folding of other proteins.[12] A well studied example is the bacterial GroEL system, which assists in the folding of globular proteins. In eukaryotic organisms chaperones are known as heat shock proteins. Although most globular proteins are able to assume their native state unassisted, chaperone-assisted folding is often necessary in the crowded intracellular environment to prevent aggregation; chaperones are also used to prevent misfolding and aggregation that may occur as a consequence of exposure to heat or other changes in the cellular environment.

There are two models of protein folding that are currently being confirmed:

  • The diffusion collision model, in which a nucleus is formed, then the secondary structure is formed, and finally these secondary structures are collided together and pack tightly together.
  • The nucleation-condensation model, in which the secondary and tertiary structures of the protein are made at the same time.

Recent studies have shown that some proteins show characteristics of both of these folding models.

For the most part, scientists have been able to study many identical molecules folding together en masse. At the coarsest level, it appears that in transitioning to the native state, a given amino acid sequence takes on roughly the same route and proceeds through roughly the same intermediates and transition states. Often folding involves first the establishment of regular secondary and supersecondary structures, in particular alpha helices and beta sheets, and afterward tertiary structure. Formation of quaternary structure usually involves the "assembly" or "coassembly" of subunits that have already folded. The regular alpha helix and beta sheet structures fold rapidly because they are stabilized by intramolecular hydrogen bonds, as was first characterized by Linus Pauling. Protein folding may involve covalent bonding in the form of disulfide bridges formed between two cysteine residues or the formation of metal clusters. Shortly before settling into their more energetically favourable native conformation, molecules may pass through an intermediate "molten globule" state.

The essential fact of folding, however, remains that the amino acid sequence of each protein contains the information that specifies both the native structure and the pathway to attain that state. This is not to say that nearly identical amino acid sequences always fold similarly.[13] Conformations differ based on environmental factors as well; similar proteins fold differently based on where they are found. Folding is a spontaneous process independent of energy inputs from nucleoside triphosphates. The passage of the folded state is mainly guided by hydrophobic interactions, formation of intramolecular hydrogen bonds, and van der Waals forces, and it is opposed by conformational entropy.

Disruption of the native state[edit]

Under some conditions proteins will not fold into their biochemically functional forms. Temperatures above or below the range that cells tend to live in will cause thermally unstable proteins to unfold or "denature" (this is why boiling makes an egg white turn opaque). High concentrations of solutes, extremes of pH, mechanical forces, and the presence of chemical denaturants can do the same. Protein thermal stability is far from constant, however. For example, hyperthermophilic bacteria have been found that grow at temperatures as high as 122 °C,[14] which of course requires that their full complement of vital proteins and protein assemblies be stable at that temperature or above.

A fully denatured protein lacks both tertiary and secondary structure, and exists as a so-called random coil. Under certain conditions some proteins can refold; however, in many cases, denaturation is irreversible.[15] Cells sometimes protect their proteins against the denaturing influence of heat with enzymes known as chaperones or heat shock proteins, which assist other proteins both in folding and in remaining folded. Some proteins never fold in cells at all except with the assistance of chaperone molecules, which either isolate individual proteins so that their folding is not interrupted by interactions with other proteins or help to unfold misfolded proteins, giving them a second chance to refold properly. This function is crucial to prevent the risk of precipitation into insoluble amorphous aggregates.

Incorrect protein folding and neurodegenerative disease[edit]

Main article: Proteopathy

Aggregated proteins are associated with prion-related illnesses such as Creutzfeldt–Jakob disease, bovine spongiform encephalopathy (mad cow disease), amyloid-related illnesses such as Alzheimer's disease and familial amyloid cardiomyopathy or polyneuropathy,[16] as well as intracytoplasmic aggregation diseases such as Huntington's and Parkinson's disease.[5][17] These age onset degenerative diseases are associated with the aggregation of misfolded proteins into insoluble, extracellular aggregates and/or intracellular inclusions including cross-beta sheet amyloid fibrils. It is not completely clear whether the aggregates are the cause or merely a reflection of the loss of protein homeostasis, the balance between synthesis, folding, aggregation and protein turnover. Recently the European Medicines Agency approved the use of Tafamidis or Vyndaqel (a kinetic stabilizer of tetrameric transthyretin) for the treatment of transthyretin amyloid diseases. This suggests that the process of amyloid fibril formation (and not the fibrils themselves) causes the degeneration of post-mitotic tissue in human amyloid diseases.[18] Misfolding and excessive degradation instead of folding and function leads to a number of proteopathy diseases such as antitrypsin-associated emphysema, cystic fibrosis and the lysosomal storage diseases, where loss of function is the origin of the disorder. While protein replacement therapy has historically been used to correct the latter disorders, an emerging approach is to use pharmaceutical chaperones to fold mutated proteins to render them functional.

Effect of external factors on the folding of proteins[edit]

Several external factors such as temperature, external fields (electric, magnetic),[19] molecular crowding,[20] and limitation of space could have a big influence on the folding of proteins.[21] Modification of the local minima by external factors can also induce modifications of the folding trajectory.

Protein folding is a very finely tuned process. Hydrogen bonding between different atoms provides the force required.[22] Hydrophobic interactions between hydrophobic amino acids pack the hydrophobic residues.

The Levinthal paradox and kinetics[edit]

Levinthal's paradox is a thought experiment, also constituting a self-reference in the theory of protein folding. In 1969, Cyrus Levinthal noted that, because of the very large number of degrees of freedom in an unfolded polypeptide chain, the molecule has an astronomical number of possible conformations. An estimate of 3300 or 10143 was made in one of his papers.

The Levinthal paradox[23] observes that if a protein were folded by sequentially sampling of all possible conformations, it would take an astronomical amount of time to do so, even if the conformations were sampled at a rapid rate (on the nanosecond or picosecond scale). Based upon the observation that proteins fold much faster than this, Levinthal then proposed that a random conformational search does not occur, and the protein must, therefore, fold through a series of meta-stable intermediate states.

The duration of the folding process varies dramatically depending on the protein of interest. When studied outside the cell, the slowest folding proteins require many minutes or hours to fold primarily due to proline isomerization, and must pass through a number of intermediate states, like checkpoints, before the process is complete.[24] On the other hand, very small single-domain proteins with lengths of up to a hundred amino acids typically fold in a single step.[25] Time scales of milliseconds are the norm and the very fastest known protein folding reactions are complete within a few microseconds.[26]

Experimental techniques for studying protein folding[edit]

While inferences about protein folding can be made through mutation studies; typically, experimental techniques for studying protein folding rely on the gradual unfolding or folding of proteins and observing conformational changes using standard non-crystallographic techniques.

Protein nuclear magnetic resonance spectroscopy[edit]

Main article: Protein NMR

Protein folding is routinely studied using NMR spectroscopy, for example by monitoring hydrogen-deuterium exchange of backbone amide protons of proteins in their native state which provides both the residue-specific stability and overall stability of proteins.[27]

Circular dichroism[edit]

Main article: Circular dichroism

Circular dichroism is one of the most general and basic tools to study protein folding. Circular dichroism spectroscopy measures the absorption of circularly polarized light. In proteins, structures such as alpha helices and beta sheets are chiral, and thus absorb such light. The absorption of this light acts as a marker of the degree of foldedness of the protein ensemble. This technique has been used to measure equilibrium unfolding of the protein by measuring the change in this absorption as a function of denaturant concentration or temperature.[citation needed] A denaturant melt measures the free energy of unfolding as well as the protein's m value, or denaturant dependence. A temperature melt measures the melting temperature (Tm) of the protein. This type of spectroscopy can also be combined with fast-mixing devices, such as stopped flow, to measure protein folding kinetics and to generate chevron plots.

Dual polarisation interferometry[edit]

Dual polarisation interferometry is a surface based technique for measuring the optical properties of molecular layers. When used to characterise protein folding, it measures the conformation by determining the overall size of a monolayer of the protein and its density in real time at sub-Angstrom resolution.[28] Although real time, measurement of the kinetics of protein folding are limited to processes that occur slower than ~10 Hz. Similar to circular dichroism the stimulus for folding can be a denaturant or temperature.

Vibrational circular dichroism of proteins[edit]

The more recent developments of vibrational circular dichroism (VCD) techniques for proteins, currently involving Fourier transform (FFT) instruments, provide powerful means for determining protein conformations in solution even for very large protein molecules. Such VCD studies of proteins are often combined with X-ray diffraction of protein crystals, FT-IR data for protein solutions in heavy water (D2O), or ab initio quantum computations to provide unambiguous structural assignments that are unobtainable from CD.[citation needed]

Studies of folding with high time resolution[edit]

The study of protein folding has been greatly advanced in recent years by the development of fast, time-resolved techniques. These are experimental methods for rapidly triggering the folding of a sample of unfolded protein, and then observing the resulting dynamics. Fast techniques in use include neutron scattering,[29] ultrafast mixing of solutions, photochemical methods, and laser temperature jump spectroscopy. Among the many scientists who have contributed to the development of these techniques are Jeremy Cook, Heinrich Roder, Harry Gray, Martin Gruebele, Brian Dyer, William Eaton, Sheena Radford, Chris Dobson, Alan Fersht, Bengt Nölting and Lars Konermann.


Proteolysis is routinely used to probe the fraction unfolded under a wide range of solution conditions (e.g. Fast parallel proteolysis (FASTpp).[30][31]

Optical tweezers[edit]

Single molecule techniques, such as optical tweezers and AFM, have been used to understand protein folding mechanisms of isolated proteins as well as proteins with chaperones.[32] Optical tweezers have been used to stretch single protein molecules from their C- and N-termini and unfold them and study the subsequent refolding.[33] The technique allows one to measure folding rates at single-molecule level. For example, optical tweezers have been recently applied to study folding and unfolding of proteins involved in blood coagulation. von Willebrand factor (vWF) is a protein with an essential role in blood clot formation process. It is discovered -using single molecule optical tweezers measurement - that calcium-bound vWF acts as a shear force sensor in the blood. Shear force leads to unfolding of the A2 domain of vWF whose refolding rate is dramatically enhanced in the presence of calcium.[34] Recently, it was also shown that the simple src SH3 domain accesses multiple unfolding pathways under force.[35]

Computational methods for studying protein folding[edit]

The study of protein folding includes three main aspects related to the prediction of protein stability, kinetics and structure. A recent review summarizes the available computational methods for protein folding. [36]

Energy landscape of protein folding[edit]

The protein folding phenomenon was largely an experimental endeavor until the formulation of an energy landscape theory of proteins by Joseph Bryngelson and Peter Wolynes in the late 1980s and early 1990s. This approach introduced the principle of minimal frustration.[37] This principle says that nature has chosen amino acid sequences so that the folded state of the protein is very stable. In addition, the undesired interactions between amino acids along the folding pathway are reduced making the acquisition of the folded state a very fast process. Even though nature has reduced the level of frustration in proteins, some degree of it remains up to now as can be observed in the presence of local minima in the energy landscape of proteins. A consequence of these evolutionarily selected sequences is that proteins are generally thought to have globally "funneled energy landscapes" (coined by José Onuchic)[38] that are largely directed toward the native state. This "folding funnel" landscape allows the protein to fold to the native state through any of a large number of pathways and intermediates, rather than being restricted to a single mechanism. The theory is supported by both computational simulations of model proteins and experimental studies,[37] and it has been used to improve methods for protein structure prediction and design.[37] The description of protein folding by the leveling free-energy landscape is also consistent with the 2nd law of thermodynamics.[39] Physically, thinking of landscapes in terms of visualizable potential or total energy surfaces simply with maxima, saddle points, minima, and funnels, rather like geographic landscapes, is perhaps a little misleading. The relevant description is really a high-dimensional phase space in which manifolds might take a variety of more complicated topological forms.[40]

Modeling of protein folding[edit]

Folding@home uses Markov state models, like the one diagrammed here, to model the possible shapes and folding pathways a protein can take as it condenses from its initial randomly coiled state (left) into its native 3D structure (right).

De novo or ab initio techniques for computational protein structure prediction are related to, but strictly distinct from experimental studies of protein folding. Molecular Dynamics (MD) is an important tool for studying protein folding and dynamics in silico.[41] First equilibrium folding simulations were done using implicit solvent model and umbrella sampling.[42] Because of computational cost, ab initio MD folding simulations with explicit water are limited to peptides and very small proteins.[43][44] MD simulations of larger proteins remain restricted to dynamics of the experimental structure or its high-temperature unfolding. Long-time folding processes (beyond about 1 millisecond), like folding of small-size proteins (about 50 residues) or larger, can be accessed using coarse-grained models.[45][46][47]

The 100-petaFLOP distributed computing project Folding@home created by Vijay Pande's group at Stanford University simulates protein folding using the idle processing time of CPUs and GPUs of personal computers from volunteers. The project aims to understand protein misfolding and accelerate drug design for disease research.

Long continuous-trajectory simulations have been performed on Anton, a massively parallel supercomputer designed and built around custom ASICs and interconnects by D. E. Shaw Research. The longest published result of a simulation performed using Anton is a 2.936 millisecond simulation of NTL9 at 355 K.[48]

See also[edit]


  1. ^ Alberts B, Johnson A, Lewis J, Raff M, Roberts K, Walters P (2002). "The Shape and Structure of Proteins". Molecular Biology of the Cell; Fourth Edition. New York and London: Garland Science. ISBN 0-8153-3218-1. 
  2. ^ Anfinsen CB (Jul 1972). "The formation and stabilization of protein structure". The Biochemical Journal. 128 (4): 737–49. doi:10.1042/bj1280737. PMC 1173893free to read. PMID 4565129. 
  3. ^ Saunders R, Deane CM (Oct 2010). "Synonymous codon usage influences the local protein structure observed". Nucleic Acids Research. Oxford University Press. 38 (19): 6719–28. doi:10.1093/nar/gkq495. PMC 2965230free to read. PMID 20530529. 
  4. ^ Berg JM, Tymoczko JL, Stryer L (2002). "3. Protein Structure and Function". Biochemistry. San Francisco: W. H. Freeman. ISBN 0-7167-4684-0. 
  5. ^ a b Selkoe DJ (Dec 2003). "Folding proteins in fatal ways". Nature. 426 (6968): 900–4. Bibcode:2003Natur.426..900S. doi:10.1038/nature02264. PMID 14685251. 
  6. ^ Alberts B, Bray D, Hopkin K, Johnson A, Lewis J, Raff M, Roberts K, Walter P (2010). "Protein Structure and Function". Essential cell biology (Third ed.). New York, NY: Garland Science. pp. 120–170. ISBN 978-0-8153-4454-4. 
  7. ^ Anfinsen CB (Jul 1973). "Principles that govern the folding of protein chains". Science. 181 (4096): 223–30. Bibcode:1973Sci...181..223A. doi:10.1126/science.181.4096.223. PMID 4124164. 
  8. ^ van den Berg B, Wain R, Dobson CM, Ellis RJ (Aug 2000). "Macromolecular crowding perturbs protein refolding kinetics: implications for folding inside the cell". The EMBO Journal. 19 (15): 3870–5. doi:10.1093/emboj/19.15.3870. PMC 306593free to read. PMID 10921869. 
  9. ^ Pace CN, Shirley BA, McNutt M, Gajiwala K (Jan 1996). "Forces contributing to the conformational stability of proteins". FASEB Journal. 10 (1): 75–83. PMID 8566551. 
  10. ^ Rose GD, Fleming PJ, Banavar JR, Maritan A (Nov 2006). "A backbone-based theory of protein folding". Proceedings of the National Academy of Sciences of the United States of America. 103 (45): 16623–33. Bibcode:2006PNAS..10316623R. doi:10.1073/pnas.0606843103. PMC 1636505free to read. PMID 17075053. 
  11. ^ Deechongkit S, Nguyen H, Powers ET, Dawson PE, Gruebele M, Kelly JW (Jul 2004). "Context-dependent contributions of backbone hydrogen bonding to beta-sheet folding energetics". Nature. 430 (6995): 101–5. Bibcode:2004Natur.430..101D. doi:10.1038/nature02611. PMID 15229605. 
  12. ^ Lee S, Tsai FT (May 2005). "Molecular chaperones in protein quality control". Journal of Biochemistry and Molecular Biology. 38 (3): 259–65. doi:10.5483/BMBRep.2005.38.3.259. PMID 15943899. 
  13. ^ Alexander PA, He Y, Chen Y, Orban J, Bryan PN (Jul 2007). "The design and characterization of two proteins with 88% sequence identity but different structure and function". Proceedings of the National Academy of Sciences of the United States of America. 104 (29): 11963–8. Bibcode:2007PNAS..10411963A. doi:10.1073/pnas.0700922104. PMC 1906725free to read. PMID 17609385. 
  14. ^ Takai K, Nakamura K, Toki T, Tsunogai U, Miyazaki M, Miyazaki J, Hirayama H, Nakagawa S, Nunoura T, Horikoshi K (Aug 2008). "Cell proliferation at 122 degrees C and isotopically heavy CH4 production by a hyperthermophilic methanogen under high-pressure cultivation". Proceedings of the National Academy of Sciences of the United States of America. 105 (31): 10949–54. Bibcode:2008PNAS..10510949T. doi:10.1073/pnas.0712334105. PMC 2490668free to read. PMID 18664583. 
  15. ^ Shortle D (Jan 1996). "The denatured state (the other half of the folding equation) and its role in protein stability". FASEB Journal. 10 (1): 27–34. PMID 8566543. 
  16. ^ Hammarström P, Wiseman RL, Powers ET, Kelly JW (2003). "Prevention of transthyretin amyloid disease by changing protein misfolding energetics". Science. 299 (5607): 713–6. doi:10.1126/science.1079589. PMID 12560553. 
  17. ^ Chiti F, Dobson CM (2006). "Protein misfolding, functional amyloid, and human disease". Annual Review of Biochemistry. 75: 333–66. doi:10.1146/annurev.biochem.75.101304.123901. PMID 16756495. 
  18. ^ Johnson SM, Wiseman RL, Sekijima Y, Green NS, Adamski-Werner SL, Kelly JW (2005). "Native state kinetic stabilization as a strategy to ameliorate protein misfolding diseases: a focus on the transthyretin amyloidoses". Accounts of Chemical Research. 38 (12): 911–21. doi:10.1021/ar020073i. PMID 16359163. 
  19. ^ Ojeda-May P, Garcia ME (Jul 2010). "Electric field-driven disruption of a native beta-sheet protein conformation and generation of a helix-structure". Biophysical Journal. 99 (2): 595–9. Bibcode:2010BpJ....99..595O. doi:10.1016/j.bpj.2010.04.040. PMC 2905109free to read. PMID 20643079. 
  20. ^ van den Berg B, Ellis RJ, Dobson CM (Dec 1999). "Effects of macromolecular crowding on protein folding and aggregation". The EMBO Journal. 18 (24): 6927–33. doi:10.1093/emboj/18.24.6927. PMC 1171756free to read. PMID 10601015. 
  21. ^ Ellis RJ (Jul 2006). "Molecular chaperones: assisting assembly in addition to folding". Trends in Biochemical Sciences. 31 (7): 395–401. doi:10.1016/j.tibs.2006.05.001. PMID 16716593. 
  22. ^ Pace CN (Jul 2009). "Energetics of protein hydrogen bonds". Nature Structural & Molecular Biology. 16 (7): 681–2. doi:10.1038/nsmb0709-681. PMID 19578376. 
  23. ^ Levinthal, Cyrus (1968). "Are there pathways for protein folding?" (PDF). Journal de Chimie Physique et de Physico-Chimie Biologique. 65: 44–45. Archived from the original (PDF) on 2009-09-02. 
  24. ^ Kim PS, Baldwin RL (1990). "Intermediates in the folding reactions of small proteins". Annual Review of Biochemistry. 59 (1): 631–60. doi:10.1146/ PMID 2197986. 
  25. ^ Jackson SE (August 1998). "How do small single-domain proteins fold?". Folding & Design. 3 (4): R81–91. doi:10.1016/S1359-0278(98)00033-9. PMID 9710577. [dead link]
  26. ^ Kubelka J, Hofrichter J, Eaton WA (Feb 2004). "The protein folding 'speed limit'". Current Opinion in Structural Biology. 14 (1): 76–88. doi:10.1016/ PMID 15102453. 
  27. ^ Beatrice M.P. Huyghues-Despointes, C. Nick Pace, S. Walter Englander, and J. Martin Scholtz. "Measuring the Conformational Stability of a Protein by Hydrogen Exchange." Methods in Molecular Biology. Kenneth P. Murphy Ed. Humana Press, Totowa, New Jersey, 2001. Pg. 69-92
  28. ^ Cross GH, Freeman NJ, Swann MJ (2008). "Dual Polarization Interferometry: A Real-Time Optical Technique for Measuring (Bio)molecular Orientation, Structure and Function at the Solid/Liquid Interface". Handbook of Biosensors and Biochips. doi:10.1002/9780470061565.hbb055. 
  29. ^ Bu Z, Cook J, Callaway DJ (Sep 2001). "Dynamic regimes and correlated structural dynamics in native and denatured alpha-lactalbumin". Journal of Molecular Biology. 312 (4): 865–73. doi:10.1006/jmbi.2001.5006. PMID 11575938. 
  30. ^ Minde DP, Maurice MM, Rüdiger SG (2012). "Determining biophysical protein stability in lysates by a fast proteolysis assay, FASTpp". PloS One. 7 (10): e46147. Bibcode:2012PLoSO...746147M. doi:10.1371/journal.pone.0046147. PMC 3463568free to read. PMID 23056252. 
  31. ^ Park C, Marqusee S (Mar 2005). "Pulse proteolysis: a simple method for quantitative determination of protein stability and ligand binding". Nature Methods. 2 (3): 207–12. doi:10.1038/nmeth740. PMID 15782190. 
  32. ^ Mashaghi A, Kramer G, Lamb DC, Mayer MP, Tans SJ (2014). "Chaperone action at the single-molecule level". Chemical Reviews. 114 (1): 660–76. doi:10.1021/cr400326k. PMID 24001118. 
  33. ^ Jagannathan B, Marqusee S (Nov 2013). "Protein folding and unfolding under force". Biopolymers. 99 (11): 860–9. doi:10.1002/bip.22321. PMC 4065244free to read. PMID 23784721. 
  34. ^ Jakobi AJ, Mashaghi A, Tans SJ, Huizinga EG. Calcium modulates force sensing by the von Willebrand factor A2 domain. Nature Commun. 2011 Jul 12;2:385. [1]
  35. ^ Jagannathan B, Elms PJ, Bustamante C, Marqusee S (Oct 2012). "Direct observation of a force-induced switch in the anisotropic mechanical unfolding pathway of a protein". Proceedings of the National Academy of Sciences of the United States of America. 109 (44): 17820–5. doi:10.1073/pnas.1201800109. PMC 3497811free to read. PMID 22949695. 
  36. ^ Compiani M, Capriotti E (Dec 2013). "Computational and theoretical methods for protein folding" (PDF). Biochemistry. 52 (48): 8601–24. doi:10.1021/bi4001529. PMID 24187909. 
  37. ^ a b c Bryngelson JD, Onuchic JN, Socci ND, Wolynes PG (Mar 1995). "Funnels, pathways, and the energy landscape of protein folding: a synthesis" (PDF). Proteins. 21 (3): 167–95. doi:10.1002/prot.340210302. PMID 7784423. 
  38. ^ Leopold PE, Montal M, Onuchic JN (Sep 1992). "Protein folding funnels: a kinetic approach to the sequence-structure relationship" (PDF). Proceedings of the National Academy of Sciences of the United States of America. 89 (18): 8721–5. Bibcode:1992PNAS...89.8721L. doi:10.1073/pnas.89.18.8721. PMC 49992free to read. PMID 1528885. 
  39. ^ Sharma V, Kaila VR, Annila A (2009). "Protein folding as an evolutionary process". Physica A. 388 (6): 851–862. Bibcode:2009PhyA..388..851S. doi:10.1016/j.physa.2008.12.004. 
  40. ^ Robson B, Vaithilingam A (2008). "Protein folding revisited". Progress in Molecular Biology and Translational Science. 84: 161–202. doi:10.1016/S0079-6603(08)00405-4. PMID 19121702. 
  41. ^ Rizzuti B, Daggett V (Mar 2013). "Using simulations to provide the framework for experimental protein folding studies". Archives of Biochemistry and Biophysics. 531 (1-2): 128–35. doi:10.1016/ PMID 23266569. 
  42. ^ Schaefer M, Bartels C, Karplus M (Dec 1998). "Solution conformations and thermodynamics of structured peptides: molecular dynamics simulation with an implicit solvation model". Journal of Molecular Biology. 284 (3): 835–48. doi:10.1006/jmbi.1998.2172. PMID 9826519. 
  43. ^ "Fragment-based Protein Folding Simulations". 
  44. ^ "Protein folding" (by Molecular Dynamics). 
  45. ^ Kmiecik, Sebastian; Gront, Dominik; Kolinski, Michal; Wieteska, Lukasz; Dawid, Aleksandra Elzbieta; Kolinski, Andrzej (2016-06-22). "Coarse-Grained Protein Models and Their Applications". Chemical Reviews. doi:10.1021/acs.chemrev.6b00163. ISSN 0009-2665. 
  46. ^ Kmiecik S, Kolinski A (Jul 2007). "Characterization of protein-folding pathways by reduced-space modeling". Proceedings of the National Academy of Sciences of the United States of America. 104 (30): 12330–5. Bibcode:2007PNAS..10412330K. doi:10.1073/pnas.0702265104. PMC 1941469free to read. PMID 17636132. 
  47. ^ Adhikari AN, Freed KF, Sosnick TR (Oct 2012). "De novo prediction of protein folding pathways and structure using the principle of sequential stabilization". Proceedings of the National Academy of Sciences of the United States of America. 109 (43): 17442–7. doi:10.1073/pnas.1209000109. PMC 3491489free to read. PMID 23045636. 
  48. ^ Lindorff-Larsen K, Piana S, Dror RO, Shaw DE (2011). "How fast-folding proteins fold". Science. 334 (6055): 517–20. doi:10.1126/science.1208351. PMID 22034434. 

External links[edit]