In molecular biology, molecular chaperones are proteins that assist the conformational folding or unfolding and the assembly or disassembly of other macromolecular structures. Chaperones are present when the macromolecules perform their normal biological functions and have correctly completed the processes of folding and/or assembly. The chaperones are concerned primarily with protein folding. The first protein to be called a chaperone assists the assembly of nucleosomes from folded histones and DNA and such assembly chaperones, especially in the nucleus, are concerned with the assembly of folded subunits into oligomeric structures.
One major function of chaperones is to prevent both newly synthesised polypeptide chains and assembled subunits from aggregating into nonfunctional structures. It is for this reason that many chaperones, but by no means all, are heat shock proteins because the tendency to aggregate increases as proteins are denatured by stress. In this case, chaperones do not convey any additional steric information required for proteins to fold. However, some highly specific 'steric chaperones' do convey unique structural (steric) information onto proteins, which cannot be folded spontaneously. Such proteins violate Anfinsen's dogma, requiring protein dynamics to fold correctly.
Various approaches have been applied to study the structure, dynamics and functioning of chaperones. Bulk biochemical measurements have informed us on the protein folding efficiency, and prevention of aggregation when chaperones are present during protein folding. Recent advances in single-molecule analysis have brought insights into structural heterogeneity of chaperones, folding intermediates and affinity of chaperones for unstructured and structured protein chains.
Location and functions
Some chaperone systems work as foldases: they support the folding of proteins in an ATP-dependent manner (for example, the GroEL/GroES or the DnaK/DnaJ/GrpE system). Although most newly synthesized proteins can fold in absence of chaperones, a minority strictly requires them for the same. Other chaperones work as holdases: they bind folding intermediates to prevent their aggregation, for example DnaJ or Hsp33. Chaperones can also work as disaggregases, i.e. they can interact with aberrant protein assemblies and revent them to monomers. Some chaperones can assist in protein degradation, leading proteins to protease systems, such as the ubiquitin-proteasome system in eukaryotes.
Many chaperones are heat shock proteins, that is, proteins expressed in response to elevated temperatures or other cellular stresses. The reason for this behaviour is that protein folding is severely affected by heat and, therefore, some chaperones act to prevent or correct damage caused by misfolding.
Macromolecular crowding may be important in chaperone function. The crowded environment of the cytosol can accelerate the folding process, since a compact folded protein will occupy less volume than an unfolded protein chain. However, crowding can reduce the yield of correctly folded protein by increasing protein aggregation. Crowding may also increase the effectiveness of the chaperone proteins such as GroEL, which could counteract this reduction in folding efficiency.
More information on the various types and mechanisms of a subset of chaperones that encapsulate their folding substrates (e.g. GroES) can be found in the article for chaperonins. Chaperonins are characterized by a stacked double-ring structure and are found in prokaryotes, in the cytosol of eukaryotes, and in mitochondria.
Other types of chaperones are involved in transport across membranes, for example membranes of the mitochondria and endoplasmic reticulum (ER) in eukaryotes. A bacterial translocation—specific chaperone maintains newly synthesized precursor polypeptide chains in a translocation-competent (generally unfolded) state and guides them to the translocon.
New functions for chaperones continue to be discovered, such as bacterial adhesin activity, induction of aggregation towards non-amyloid aggregates, suppression of toxic protein oligomers via their clustering, and in responding to diseases linked to protein aggregation (e.g. see prion) and cancer maintenance.
Human chaperone proteins
Chaperones are found in, for example, the endoplasmic reticulum (ER), since protein synthesis often occurs in this area.
In the endoplasmic reticulum (ER) there are general, lectin- and non-classical molecular chaperones helping to fold proteins.
- General chaperones: GRP78/BiP, GRP94, GRP170.
- Lectin chaperones: calnexin and calreticulin
- Non-classical molecular chaperones: HSP47 and ERp29
- Folding chaperones:
Nomenclature and examples of bacterial and archaeal chaperones
There are many different families of chaperones; each family acts to aid protein folding in a different way. In bacteria like E. coli, many of these proteins are highly expressed under conditions of high stress, for example, when the bacterium is placed in high temperatures. For this reason, the term "heat shock protein" has historically been used to name these chaperones. The prefix "Hsp" designates that the protein is a heat shock protein.
Hsp60 (GroEL/GroES complex in E. coli) is the best characterized large (~ 1 MDa) chaperone complex. GroEL is a double-ring 14mer with a hydrophobic patch at its opening; it is so large it can accommodate native folding of 54-kDa GFP in its lumen. GroES is a single-ring heptamer that binds to GroEL in the presence of ATP or ADP. GroEL/GroES may not be able to undo previous aggregation, but it does compete in the pathway of misfolding and aggregation. Also acts in mitochondrial matrix as molecular chaperone.
Hsp70 (DnaK in E. coli) is perhaps the best characterized small (~ 70 kDa) chaperone.
The Hsp70 proteins are aided by Hsp40 proteins (DnaJ in E. coli), which increase the ATP consumption rate and activity of the Hsp70s.
It has been noted that increased expression of Hsp70 proteins in the cell results in a decreased tendency toward apoptosis.
Although a precise mechanistic understanding has yet to be determined, it is known that Hsp70s have a high-affinity bound state to unfolded proteins when bound to ADP, and a low-affinity state when bound to ATP.
It is thought that many Hsp70s crowd around an unfolded substrate, stabilizing it and preventing aggregation until the unfolded molecule folds properly, at which time the Hsp70s lose affinity for the molecule and diffuse away. Hsp70 also acts as a mitochondrial and chloroplastic molecular chaperone in eukaryotes.
Hsp90 (HtpG in E. coli) may be the least understood chaperone. Its molecular weight is about 90 kDa, and it is necessary for viability in eukaryotes (possibly for prokaryotes as well).
Heat shock protein 90 (Hsp90) is a molecular chaperone essential for activating many signaling proteins in the eukaryotic cell.
Each Hsp90 has an ATP-binding domain, a middle domain, and a dimerization domain. Originally thought to clamp onto their substrate protein (also known as a client protein) upon binding ATP, the recently published structures by Vaughan et al. and Ali et al. indicate that client proteins may bind externally to both the N-terminal and middle domains of Hsp90.
Proteins in the Hsp100/Clp family form large hexameric structures with unfoldase activity in the presence of ATP. These proteins are thought to function as chaperones by processively threading client proteins through a small 20 Å (2 nm) pore, thereby giving each client protein a second chance to fold.
Some of these Hsp100 chaperones, like ClpA and ClpX, associate with the double-ringed tetradecameric serine protease ClpP; instead of catalyzing the refolding of client proteins, these complexes are responsible for the targeted destruction of tagged and misfolded proteins.
The investigation of chaperones has a long history. The term "molecular chaperone" appeared first in the literature in 1978, and was invented by Ron Laskey to describe the ability of a nuclear protein called nucleoplasmin to prevent the aggregation of folded histone proteins with DNA during the assembly of nucleosomes. The term was later extended by R. John Ellis in 1987 to describe proteins that mediated the post-translational assembly of protein complexes. In 1988, it was realised that similar proteins mediated this process in both prokaryotes and eukaryotes. The details of this process were determined in 1989, when the ATP-dependent protein folding was demonstrated in vitro.
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- Biological machines
- Chemical chaperones
- Heat shock protein
- Protein dynamics
- Molecular chaperone therapy
- Richardson RT, Alekseev OM, Grossman G, Widgren EE, Thresher R, Wagner EJ, et al. (July 2006). "Nuclear autoantigenic sperm protein (NASP), a linker histone chaperone that is required for cell proliferation". The Journal of Biological Chemistry. 281 (30): 21526–34. doi:10.1074/jbc.M603816200. PMID 16728391.
- Alekseev OM, Richardson RT, Alekseev O, O'Rand MG (May 2009). "Analysis of gene expression profiles in HeLa cells in response to overexpression or siRNA-mediated depletion of NASP". Reproductive Biology and Endocrinology. 7: 45. doi:10.1186/1477-7827-7-45. PMC 2686705. PMID 19439102.
- Ellis RJ (July 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.
- Pauwels K, Van Molle I, Tommassen J, Van Gelder P (May 2007). "Chaperoning Anfinsen: the steric foldases" (PDF). Molecular Microbiology. 64 (4): 917–22. doi:10.1111/j.1365-2958.2007.05718.x. PMID 17501917. Archived from the original (PDF) on 2012-05-23.
- [Chaperone Action at the Single-Molecule Level http://pubs.acs.org/doi/abs/10.1021/cr400326k]
- Hoffmann JH, Linke K, Graf PC, Lilie H, Jakob U (January 2004). "Identification of a redox-regulated chaperone network". The EMBO Journal. 23 (1): 160–8. doi:10.1038/sj.emboj.7600016. PMC 1271656. PMID 14685279.
- Nillegoda NB, Kirstein J, Szlachcic A, Berynskyy M, Stank A, Stengel F, et al. (August 2015). "Crucial HSP70 co-chaperone complex unlocks metazoan protein disaggregation". Nature. 524 (7564): 247–51. Bibcode:2015Natur.524..247N. doi:10.1038/nature14884. PMC 4830470. PMID 26245380.
- Balchin D, Hayer-Hartl M, Hartl FU (July 2016). "In vivo aspects of protein folding and quality control". Science. 353 (6294): aac4354. doi:10.1126/science.aac4354. hdl:11858/00-001M-0000-002B-0856-C. PMID 27365453.
- Ellis RJ, van der Vies SM (1991). "Molecular chaperones". Annual Review of Biochemistry. 60: 321–47. doi:10.1146/annurev.bi.60.070191.001541. PMID 1679318.
- van den Berg B, Wain R, Dobson CM, Ellis RJ (August 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 306593. PMID 10921869.
- van den Berg B, Ellis RJ, Dobson CM (December 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 1171756. PMID 10601015.
- Ellis RJ, Minton AP (May 2006). "Protein aggregation in crowded environments". Biological Chemistry. 387 (5): 485–97. doi:10.1515/BC.2006.064. PMID 16740119.
- Martin J, Hartl FU (February 1997). "The effect of macromolecular crowding on chaperonin-mediated protein folding". Proceedings of the National Academy of Sciences of the United States of America. 94 (4): 1107–12. Bibcode:1997PNAS...94.1107M. doi:10.1073/pnas.94.4.1107. PMC 19752. PMID 9037014.
- Ellis RJ (2007). Protein misassembly: macromolecular crowding and molecular chaperones. Adv. Exp. Med. Biol. Advances in Experimental Medicine and Biology. 594. New York, N.Y. : Sprinter Science+Business Media, LLC ; Austin, Tex. : Landes Bioscience/Eurekah.com. pp. 1–13. doi:10.1007/978-0-387-39975-1_1. ISBN 978-0-387-39974-4. PMID 17205670.
- Zhou J, Xu Z (October 2005). "The structural view of bacterial translocation-specific chaperone SecB: implications for function" (PDF). Molecular Microbiology. 58 (2): 349–57. doi:10.1111/j.1365-2958.2005.04842.x. hdl:2027.42/74325. PMID 16194224.
- Specht S, Miller SB, Mogk A, Bukau B (14 November 2011). "Hsp42 is required for sequestration of protein aggregates into deposition sites in Saccharomyces cerevisiae". J. Cell Biol. 195 (4): 617–29. doi:10.1083/jcb.201106037. PMC 3257523. PMID 22065637.
- Ojha J, Masilamoni G, Dunlap D, Udoff RA, Cashikar AG (August 2011). "Sequestration of toxic oligomers by HspB1 as a cytoprotective mechanism". Mol. Cell. Biol. 31 (15): 3146–57. doi:10.1128/MCB.01187-10. PMC 3147607. PMID 21670152.
- Mannini B, Cascella R, Zampagni M, van Waarde-Verhagen M, Meehan S, Roodveldt C, Campioni S, Boninsegna M, Penco A, Relini A, Kampinga HH, Dobson CM, Wilson MR, Cecchi C, Chiti F (31 July 2012). "Molecular mechanisms used by chaperones to reduce the toxicity of aberrant protein oligomers". Proc. Natl. Acad. Sci. USA. 109 (31): 12479–84. Bibcode:2012PNAS..10912479M. doi:10.1073/pnas.1117799109. PMC 3411936. PMID 22802614.
- Sadigh-Eteghad S, Majdi A, Talebi M, Mahmoudi J, Babri S (May 2015). "Regulation of nicotinic acetylcholine receptors in Alzheimer׳s disease: a possible role of chaperones". European Journal of Pharmacology. 755: 34–41. doi:10.1016/j.ejphar.2015.02.047. PMID 25771456.
- Salamanca HH, Antonyak MA, Cerione RA, Shi H, Lis JT (2014). "Inhibiting heat shock factor 1 in human cancer cells with a potent RNA aptamer". PLOS ONE. 9 (5): e96330. Bibcode:2014PLoSO...996330S. doi:10.1371/journal.pone.0096330. PMC 4011729. PMID 24800749.
- Ruoppolo M, Orrù S, Talamo F, Ljung J, Pirneskoski A, Kivirikko KI, et al. (May 2003). "Mutations in domain a' of protein disulfide isomerase affect the folding pathway of bovine pancreatic ribonuclease A". Protein Science. 12 (5): 939–52. doi:10.1110/ps.0242803. PMC 2323865. PMID 12717017.
- Soluble complexes of target proteins and peptidyl prolyl isomerase ...
- Frickel EM, Riek R, Jelesarov I, Helenius A, Wuthrich K, Ellgaard L (February 2002). "TROSY-NMR reveals interaction between ERp57 and the tip of the calreticulin P-domain". Proceedings of the National Academy of Sciences of the United States of America. 99 (4): 1954–9. Bibcode:2002PNAS...99.1954F. doi:10.1073/pnas.042699099. PMC 122301. PMID 11842220.
- Fenton WA, Horwich AL (May 2003). "Chaperonin-mediated protein folding: fate of substrate polypeptide". Quarterly Reviews of Biophysics. 36 (2): 229–56. doi:10.1017/S0033583503003883. PMID 14686103. S2CID 10328521.
- Mayer MP, Bukau B (March 2005). "Hsp70 chaperones: cellular functions and molecular mechanism". Cellular and Molecular Life Sciences. 62 (6): 670–84. doi:10.1007/s00018-004-4464-6. PMC 2773841. PMID 15770419.
- Vaughan CK, Gohlke U, Sobott F, Good VM, Ali MM, Prodromou C, et al. (September 2006). "Structure of an Hsp90-Cdc37-Cdk4 complex". Molecular Cell. 23 (5): 697–707. doi:10.1016/j.molcel.2006.07.016. PMC 5704897. PMID 16949366.
- Ali MM, Roe SM, Vaughan CK, Meyer P, Panaretou B, Piper PW, et al. (April 2006). "Crystal structure of an Hsp90-nucleotide-p23/Sba1 closed chaperone complex". Nature. 440 (7087): 1013–7. Bibcode:2006Natur.440.1013A. doi:10.1038/nature04716. PMC 5703407. PMID 16625188.
- Terasawa K, Minami M, Minami Y (April 2005). "Constantly updated knowledge of Hsp90". Journal of Biochemistry. 137 (4): 443–7. doi:10.1093/jb/mvi056. PMID 15858167.
- Pearl LH, Prodromou C (2006). "Structure and mechanism of the Hsp90 molecular chaperone machinery". Annual Review of Biochemistry. 75: 271–94. doi:10.1146/annurev.biochem.75.103004.142738. PMID 16756493.
- Ellis RJ (September 1996). "Discovery of molecular chaperones". Cell Stress & Chaperones. 1 (3): 155–60. doi:10.1379/1466-1268(1996)001<0155:DOMC>2.3.CO;2. PMC 248474. PMID 9222600.
- Laskey RA, Honda BM, Mills AD, Finch JT (October 1978). "Nucleosomes are assembled by an acidic protein which binds histones and transfers them to DNA". Nature. 275 (5679): 416–20. Bibcode:1978Natur.275..416L. doi:10.1038/275416a0. PMID 692721.
- Ellis J (1987). "Proteins as molecular chaperones". Nature. 328 (6129): 378–9. doi:10.1038/328378a0. PMID 3112578.
- Hemmingsen SM, Woolford C, van der Vies SM, Tilly K, Dennis DT, Georgopoulos CP, et al. (May 1988). "Homologous plant and bacterial proteins chaperone oligomeric protein assembly". Nature. 333 (6171): 330–4. Bibcode:1988Natur.333..330H. doi:10.1038/333330a0. PMID 2897629.
- Goloubinoff P, Christeller JT, Gatenby AA, Lorimer GH (1989). "Reconstitution of active dimeric ribulose bisphosphate carboxylase from an unfoleded state depends on two chaperonin proteins and Mg-ATP". Nature. 342 (6252): 884–9. Bibcode:1989Natur.342..884G. doi:10.1038/342884a0. PMID 10532860.
- Taylor JP (August 2015). "Multisystem proteinopathy: intersecting genetics in muscle, bone, and brain degeneration". Neurology. 85 (8): 658–60. doi:10.1212/WNL.0000000000001862. PMID 26208960. S2CID 42203997.