Hsp90 (heat shock protein 90) 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.
Heat shock proteins, as a class, are among the most highly expressed cellular proteins across all species.[3] As their name implies, heat shock proteins protect cells when stressed by elevated temperatures. They account for 1–2% of total protein in unstressed cells. However, when cells are heated, the fraction of heat shock proteins increases to 4–6% of cellular proteins.[4]
Heat shock protein 90 (Hsp90) is one of the most common of the heat-related proteins. The "90" comes from the fact that it has a mass of roughly 90 kilodaltons. A 90 kDa protein is considered fairly large for a non-fibrous protein. Hsp90 is found in bacteria and all branches of eukarya, but it is apparently absent in archaea.[5] Whereas cytoplasmic Hsp90 is essential for viability under all conditions in eukaryotes, the bacterial homologue HtpG is dispensable under non-heat stress conditions.[6]
This protein was first isolated by extracting proteins from cells stressed by heating, dehydrating or by other means, all of which caused the cell's proteins to begin to denature.[7] However it was later discovered that Hsp90 also has essential functions in unstressed cells.
^Prodromou C, Roe SM, Piper PW, Pearl LH (June 1997). "A molecular clamp in the crystal structure of the N-terminal domain of the yeast Hsp90 chaperone". Nat. Struct. Biol. 4 (6): 477–82. doi:10.1038/nsb0697-477. PMID9187656. S2CID38764610.
^Csermely P, Schnaider T, Soti C, Prohászka Z, Nardai G (August 1998). "The 90-kDa molecular chaperone family: structure, function, and clinical applications. A comprehensive review". Pharmacol. Ther. 79 (2): 129–68. doi:10.1016/S0163-7258(98)00013-8. PMID9749880.