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In molecular biology, molecular chaperones are proteins that assist the conformational folding or unfolding of large proteins or macromolecular protein complexes. There are a number of classes of molecular chaperones, all of which function to assist large proteins in proper protein folding during or after synthesis, and after partial denaturation. Chaperones are also involved in the translocation of proteins for proteolysis.
Ribulose-1,5-bisphosphate carboxylase/oxygenase, commonly known by the abbreviations RuBisCo, rubisco, RuBPCase, or RuBPco, is an enzyme involved in the first major step of carbon fixation, a process by which atmospheric carbon dioxide is converted by plants and other photosynthetic organisms to energy-rich molecules such as glucose. In chemical terms, it catalyzes the carboxylation of ribulose-1,5-bisphosphate. It is probably the most abundant enzyme on Earth.
Ribulose 1,5-bisphosphate (RuBP) is an organic substance that is involved in photosynthesis, notably as the principal CO2 acceptor in plants. It is a colourless anion, a double phosphate ester of the ketopentose called ribulose. Salts of RuBP can be isolated, but its crucial biological function happens in solution. RuBP occurs not only in plants but in all domains of life, including Archaea, Bacteria, and Eukarya.
The Calvin cycle,light-independent reactions, bio synthetic phase,dark reactions, or photosynthetic carbon reduction (PCR) cycle of photosynthesis is a series of chemical reactions that convert carbon dioxide and hydrogen-carrier compounds into glucose. The Calvin cycle is present in all photosynthetic eukaryotes and also many photosynthetic bacteria. In plants, these reactions occur in the stroma, the fluid-filled region of a chloroplast outside the thylakoid membranes. These reactions take the products of light-dependent reactions and perform further chemical processes on them. The Calvin cycle uses the chemical energy of ATP and reducing power of NADPH from the light dependent reactions to produce sugars for the plant to use. These substrates are used in a series of reduction-oxidation reactions to produce sugars in a step-wise process; there is no direct reaction that converts several molecules of CO2 to a sugar. There are three phases to the light-independent reactions, collectively called the Calvin cycle: carboxylation, reduction reactions, and ribulose 1,5-bisphosphate (RuBP) regeneration.
GroEL is a protein which belongs to the chaperonin family of molecular chaperones, and is found in many bacteria. It is required for the proper folding of many proteins. To function properly, GroEL requires the lid-like cochaperonin protein complex GroES. In eukaryotes the organellar proteins Hsp60 and Hsp10 are structurally and functionally nearly identical to GroEL and GroES, respectively, due to their endosymbiotic origin.
HSP60, also known as chaperonins (Cpn), is a family of heat shock proteins originally sorted by their 60kDa molecular mass. They prevent misfolding of proteins during stressful situations such as high heat, by assisting protein folding. HSP60 belong to a large class of molecules that assist protein folding, called molecular chaperones.
Acetyl-CoA carboxylase (ACC) is a biotin-dependent enzyme that catalyzes the irreversible carboxylation of acetyl-CoA to produce malonyl-CoA through its two catalytic activities, biotin carboxylase (BC) and carboxyltransferase (CT). ACC is a multi-subunit enzyme in most prokaryotes and in the chloroplasts of most plants and algae, whereas it is a large, multi-domain enzyme in the cytoplasm of most eukaryotes. The most important function of ACC is to provide the malonyl-CoA substrate for the biosynthesis of fatty acids. The activity of ACC can be controlled at the transcriptional level as well as by small molecule modulators and covalent modification. The human genome contains the genes for two different ACCs—ACACA and ACACB.
Carboxylation is a chemical reaction in which a carboxylic acid is produced by treating a substrate with carbon dioxide. The opposite reaction is decarboxylation. In chemistry, the term carbonation is sometimes used synonymously with carboxylation, especially when applied to the reaction of carbanionic reagents with CO2. More generally, carbonation usually describes the production of carbonates.
Prefoldin (GimC) is a superfamily of proteins used in protein folding complexes. It is classified as a heterohexameric molecular chaperone in both archaea and eukarya, including humans. A prefoldin molecule works as a transfer protein in conjunction with a molecule of chaperonin to form a chaperone complex and correctly fold other nascent proteins. One of prefoldin's main uses in eukarya is the formation of molecules of actin for use in the eukaryotic cytoskeleton.
Chaperonin ATPase (EC 3.6.4.9, chaperonin) is an enzyme with systematic name ATP phosphohydrolase (polypeptide-unfolding). This enzyme catalyses the following chemical reaction
Arthur L. Horwich is an American biologist and Sterling Professor of Genetics and Pediatrics at the Yale School of Medicine. Horwich has also been a Howard Hughes Medical Institute investigator since 1990. His research into protein folding uncovered the action of chaperonins, protein complexes that assist the folding of other proteins; Horwich first published this work in 1989.
In enzymology, a [ribulose-bisphosphate carboxylase]-lysine N-methyltransferase (EC 2.1.1.127) is an enzyme that catalyzes the chemical reaction
Phosphoribulokinase (PRK) (EC 2.7.1.19) is an essential photosynthetic enzyme that catalyzes the ATP-dependent phosphorylation of ribulose 5-phosphate (RuP) into ribulose 1,5-bisphosphate (RuBP), both intermediates in the Calvin Cycle. Its main function is to regenerate RuBP, which is the initial substrate and CO2-acceptor molecule of the Calvin Cycle. PRK belongs to the family of transferase enzymes, specifically those transferring phosphorus-containing groups (phosphotransferases) to an alcohol group acceptor. Along with ribulose 1,5-bisphosphate carboxylase/oxygenase (RuBisCo), phosphoribulokinase is unique to the Calvin Cycle. Therefore, PRK activity often determines the metabolic rate in organisms for which carbon fixation is key to survival. Much initial work on PRK was done with spinach leaf extracts in the 1950s; subsequent studies of PRK in other photosynthetic prokaryotic and eukaryotic organisms have followed. The possibility that PRK might exist was first recognized by Weissbach et al. in 1954; for example, the group noted that carbon dioxide fixation in crude spinach extracts was enhanced by the addition of ATP. The first purification of PRK was conducted by Hurwitz and colleagues in 1956.
ATP + Mg2+ - D-ribulose 5-phosphate ADP + D-ribulose 1,5-bisphosphate
T-complex protein 1 subunit epsilon is a protein that in humans is encoded by the CCT5 gene.
Proteostasis is the dynamic regulation of a balanced, functional proteome. The proteostasis network includes competing and integrated biological pathways within cells that control the biogenesis, folding, trafficking, and degradation of proteins present within and outside the cell. Loss of proteostasis is central to understanding the cause of diseases associated with excessive protein misfolding and degradation leading to loss-of-function phenotypes, as well as aggregation-associated degenerative disorders. Therapeutic restoration of proteostasis may treat or resolve these pathologies. Cellular proteostasis is key to ensuring successful development, healthy aging, resistance to environmental stresses, and to minimize homeostatic perturbations from pathogens such as viruses. Cellular mechanisms for maintaining proteostasis include regulated protein translation, chaperone assisted protein folding, and protein degradation pathways. Adjusting each of these mechanisms based on the need for specific proteins is essential to maintain all cellular functions relying on a correctly folded proteome.
Steven M. Smith is Professor of Plant Genetics and Biochemistry at the University of Tasmania in Australia, and Visiting Professor in the Chinese Academy of Sciences Institute of Genetics and Developmental Biology, Beijing, China. He is also a chief investigator at the Australian Research Council Centre of Excellence for Plant Success in Nature and Agriculture.
Chaperones, also called molecular chaperones, are proteins that assist other proteins in assuming their three-dimensional fold, which is necessary for protein function. However, the fold of a protein is sensitive to environmental conditions, such as temperature and pH, and thus chaperones are needed to keep proteins in their functional fold across various environmental conditions. Chaperones are an integral part of a cell's protein quality control network by assisting in protein folding and are ubiquitous across diverse biological taxa. Since protein folding, and therefore protein function, is susceptible to environmental conditions, chaperones could represent an important cellular aspect of biodiversity and environmental tolerance by organisms living in hazardous conditions. Chaperones also affect the evolution of proteins in general, as many proteins fundamentally require chaperones to fold or are naturally prone to misfolding, and therefore mitigates protein aggregation.
Pierre A. Goloubinoff is a Swiss-Israeli biochemist, author and activist for Yemeni immigration and the preservation of Yemeni heritage. He is also known by the pen names David Hamami or Daoud Hamami.
Anthony R. Cashmore is a biochemist and plant molecular biologist, best known for identifying cryptochrome photoreceptor proteins. These specialized proteins are critical for plant development and play an essential role in circadian rhythms of plants and animals. A Professor emeritus in the Department of Biology at the University of Pennsylvania, Cashmore led the Plant Science Institute from the time of his appointment in 1986 until his retirement in 2011. He was elected to the National Academy of Sciences in 2003.
2-Phosphoglycolate (chemical formula C2H2O6P3-; also known as phosphoglycolate, 2-PG, or PG) is a natural metabolic product of the oxygenase reaction mediated by the enzyme ribulose 1,5-bisphosphate carboxylase (RuBisCo).
References
- ↑ Ellis, J. (2010) How Science Works: Evolution. Springer, Heidelberg.
- ↑ Blair, G. E.; Ellis, R. J. (1973). "Protein synthesis in chloroplasts. I. Light-driven synthesis of the large subunit of Fraction I protein by isolated pea chloroplasts". Biochim. Biophys. Acta. 319 (2): 223. doi:10.1016/0005-2787(73)90013-0. PMC 1178671 . PMID 5076673.
- ↑ Highfield, P. E.; Ellis, R. J. (1978). "Synthesis and transport of the small subunit of chloroplast ribulose bisphosphate carboxylase". Nature . 271 (5644): 420. Bibcode:1978Natur.271..420H. doi:10.1038/271420a0. S2CID 4188202.
- ↑ Barraclough, R.; Ellis, R. J. (1980). "Protein synthesis in chloroplasts IX. Assembly of newly-synthesised large subunits into ribulose bisphosphate carboxylase in isolated intact pea chloroplasts". Biochim. Biophys. Acta. 608 (1): 19–31. doi:10.1016/0005-2787(80)90129-x. PMID 7388030.
- ↑ Ellis, R. J. (1987). "Proteins as molecular chaperones". Nature. 328 (6129): 378–9. doi:10.1038/328378a0. PMID 3112578. S2CID 4337273.
- ↑ Hemmingsen, S. M.; Woolford, C.; van der Vies, S. M.; Tilly, K.; Dennis, D. T.; Georgopoulos, C. P.; Hendrix, R. W.; Ellis, R. J. (1988). "Homologous plant and bacterial proteins chaperone oligomeric protein assembly". Nature. 333 (6171): 330–334. Bibcode:1988Natur.333..330H. doi:10.1038/333330a0. PMID 2897629. S2CID 4325057.
- ↑ van den Berg, B.; Wain, R.; Dobson, C. M.; Ellis, R. J. (2000). "Macromolecular crowding perturbs protein refolding kinetics: implications for protein folding inside the cell". EMBO J. 19 (15): 3870–3875. doi:10.1093/emboj/19.15.3870. PMC 306593 . PMID 10921869.
- ↑ R. John Ellis Archived 28 August 2008 at the Wayback Machine , awardee of The Gairdner Foundation.
- ↑ "2019 Winners". www.biochemistry.org. Archived from the original on 8 April 2018.
