However, when cells are heated, the fraction of heat shock proteins increases to 4–6% of cellular proteins. They account for 1–2% of total protein in unstressed cells. As their name implies, heat shock proteins protect cells when stressed by elevated temperatures. Heat shock proteins, as a class, are among the most highly expressed cellular proteins across all species. It also stabilizes a number of proteins required for tumor growth, which is why Hsp90 inhibitors are investigated as anti-cancer drugs. 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. Also, X-X represents a mature properly folded protein dimer. Hsp40, Hsp70, and p23 are partner chaperones while Hop is a co-chaperone. X/Y represents an immature incompletely folded protein such a steroid receptor. NTD = N-terminal domain, MD = middle domain, CTD = C-terminal domain. Pincer movement of Hsp90 coupled to the ATPase cycle. Crystallographic structure of the ATP binding pocket of Hsp90 where ATP is represented by a ball and stick figure (carbon atoms = grey, nitrogen = blue, oxygen = red, phosphorus = orange) and Hsp90 is depicted as a solid surface (negatively charged = red, positively charged = blue, electrostatically neutral = grey). NTD= N-terminal domain (red), MD = middle domain (green), CTD = C-terminal domain (blue). Bound ATP molecules are represented by space filling spheres. Top: Crystallographic structure of the dimeric Hsp90. ĭomain structure of the yeast heat-inducible Hsp90. Structure of the N-terminal domain of the yeast Hsp90 chaperone.
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