Co-chaperones are proteins that assist chaperones in protein folding and other functions. Co-chaperones are the non-client binding molecules that assist in protein folding mediated by Hsp70 and Hsp90. They are particularly essential in stimulation of the ATPase activity of these chaperone proteins. There are a great number of different co-chaperones however based on their domain structure most of them fall into two groups: J-domain proteins and tetratricopeptide repeats (TPR). [1]
Co-chaperones assist heat shock proteins in the protein folding process. These co-chaperones can function in a number of ways. Primarily co-chaperones are involved in the ATPase functionality of their associated heat shock proteins. Co-chaperones catalyze the hydrolysis ATP to ADP on their respective chaperones which then allows them undergo a large conformational change that allows them to either bind to their substrates with higher affinity or aid in the release of the substrate following protein folding, as in the case of co-chaperone p23. [2]
J-proteins, DnaJ or Hsp40 are important co-chaperones for Hsp70 and have the ability to bind to polypeptides and then recruit chaperone protein DnaK and passes the polypeptide along to this chaperone by catalyzing ATP hydrolysis that allows DnaK to bind to the unfolded polypeptide with high affinity. Another co-chaperone, GrpE, comes in following the folding of this protein to cause a conformational change in DnaK that allows it to release the folded protein. [3] The mechanism of TPR proteins is less studied these domains have been shown to interact with Hsp90 and Hsp70 and may be involved in the creation of an Hsp70-Hsp90 multi-chaperone complex. [4]
Co-chaperones may also play an important role in misfolding diseases such as cystic fibrosis. An interaction between Hsp90 and its co-chaperone, Aha1, is essential to the proper folding of cystic fibrosis transmembrane conductance regulator (CFTR). [5] Other examples of co-chaperone's role in illness include neurodegenerative diseases. Alzheimer’s and Parkinson’s disease have a number of proteins that can aggregate if not properly chaperoned. Co-chaperones CSPα (DNAJC5), auxilin (DNAJC6) and RME-8 (DNAJC13) are important for preserving folding and assembly, therefore preventing protein aggregation. [6] Detection of mutations in these proteins have been associated with the early onset of neurodegenerative diseases. [7]
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.
The 70 kilodalton heat shock proteins are a family of conserved ubiquitously expressed heat shock proteins. Proteins with similar structure exist in virtually all living organisms. Intracellularly localized Hsp70s are an important part of the cell's machinery for protein folding, performing chaperoning functions, and helping to protect cells from the adverse effects of physiological stresses. Additionally, membrane-bound Hsp70s have been identified as a potential target for cancer therapies and their extracellularly localized counterparts have been identified as having both membrane-bound and membrane-free structures.
Hsp90 is a chaperone protein that assists other proteins to fold properly, stabilizes proteins against heat stress, and aids in protein degradation. It also stabilizes a number of proteins required for tumor growth, which is why Hsp90 inhibitors are investigated as anti-cancer drugs.
Cystic fibrosis transmembrane conductance regulator (CFTR) is a membrane protein and anion channel in vertebrates that is encoded by the CFTR gene.
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.
Hop, occasionally written HOP, is an abbreviation for Hsp70-Hsp90 Organizing Protein. It functions as a co-chaperone which reversibly links together the protein chaperones Hsp70 and Hsp90.
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.
The heat shock response (HSR) is a cell stress response that increases the number of molecular chaperones to combat the negative effects on proteins caused by stressors such as increased temperatures, oxidative stress, and heavy metals. In a normal cell, proteostasis must be maintained because proteins are the main functional units of the cell. Many proteins take on a defined configuration in a process known as protein folding in order to perform their biological functions. If these structures are altered, critical processes could be affected, leading to cell damage or death. The heat shock response can be employed under stress to induce the expression of heat shock proteins (HSP), many of which are molecular chaperones, that help prevent or reverse protein misfolding and provide an environment for proper folding.
Heat shock 70 kDa protein 8 also known as heat shock cognate 71 kDa protein or Hsc70 or Hsp73 is a heat shock protein that in humans is encoded by the HSPA8 gene on chromosome 11. As a member of the heat shock protein 70 family and a chaperone protein, it facilitates the proper folding of newly translated and misfolded proteins, as well as stabilize or degrade mutant proteins. Its functions contribute to biological processes including signal transduction, apoptosis, autophagy, protein homeostasis, and cell growth and differentiation. It has been associated with an extensive number of cancers, neurodegenerative diseases, cell senescence, and aging.
In eukaryotic cells, an aggresome refers to an aggregation of misfolded proteins in the cell, formed when the protein degradation system of the cell is overwhelmed. Aggresome formation is a highly regulated process that possibly serves to organize misfolded proteins into a single location.
Heat shock protein HSP 90-alpha is a protein that in humans is encoded by the HSP90AA1 gene.
Human gene HSPA1B is an intron-less gene which encodes for the heat shock protein HSP70-2, a member of the Hsp70 family of proteins. The gene is located in the major histocompatibility complex, on the short arm of chromosome 6, in a cluster with two paralogous genes, HSPA1A and HSPA1L. HSPA1A and HSPA1B produce nearly identical proteins because the few differences in their DNA sequences are almost exclusively synonymous substitutions or in the three prime untranslated region, heat shock 70kDa protein 1A, from HSPA1A, and heat shock 70kDa protein 1B, from HSPA1B. A third, more modified paralog to these genes exists in the same region, HSPA1L, which shares a 90% homology with the other two.
Heat shock factor 1 (HSF1) is a protein that in humans is encoded by the HSF1 gene. HSF1 is highly conserved in eukaryotes and is the primary mediator of transcriptional responses to proteotoxic stress with important roles in non-stress regulation such as development and metabolism.
Heat shock protein HSP 90-beta also called HSP90beta is a protein that in humans is encoded by the HSP90AB1 gene.
Binding immunoglobulin protein (BiPS) also known as 78 kDa glucose-regulated protein (GRP-78) or heat shock 70 kDa protein 5 (HSPA5) is a protein that in humans is encoded by the HSPA5 gene.
In molecular biology, protein aggregation is a phenomenon in which intrinsically-disordered or mis-folded proteins aggregate either intra- or extracellularly. Protein aggregates have been implicated in a wide variety of diseases known as amyloidoses, including ALS, Alzheimer's, Parkinson's and prion disease.
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.
In molecular biology, chaperone DnaJ, also known as Hsp40, is a molecular chaperone protein. It is expressed in a wide variety of organisms from bacteria to humans.
Chemical chaperones are a class of small molecules that function to enhance the folding and/or stability of proteins. Chemical chaperones are a broad and diverse group of molecules, and they can influence protein stability and polypeptide organization through a variety of mechanisms. Chemical chaperones are used for a range of applications, from production of recombinant proteins to treatment of protein misfolding in vivo.
Chaperome refers to the ensemble of all cellular molecular chaperone and co-chaperone proteins that assist protein folding of misfolded proteins or folding intermediates in order to ensure native protein folding and function, to antagonize aggregation-related proteotoxicity and ensuing protein loss-of-function or protein misfolding-diseases such as the neurodegenerative diseases Alzheimer's, Huntington's or Parkinson's disease, as well as to safeguard cellular proteostasis and proteome balance.