a highly conserved N-terminal domain (NTD) of ~25 kDa.Hsp90 consists of four structural domains: The 3 10 helices make up approximately 11% of the protein's amino acid residues, which is much higher than the average 4% in other proteins. Hsp90 contains nine helices and eight anti-parallel beta pleated sheets, which combine to form several alpha/beta sandwiches. Being a cytoplasmic protein requires that the protein be globular in structure, that is largely non-polar on the inside and polar on the outside, so as to be dissolved by water. The overall structure of Hsp90 is similar to that of other proteins in that it contains all of the common secondary structural elements (i.e., alpha helixes, beta pleated sheets, and random coils). It is possibly a cloning artifact or a product of chromosomal rearrangement occurring in a single cell line. However, gene-encoding Hsp90N was later proven to be non-existent in human genome. This HSP90α-Δ-N transcript is a chimera, with the first 105 bp of the coding sequence derived from the CD47 gene on chromosome 3q13.2, and the remaining coding sequence derived from HSP90AA1. There are 12 human pseudogenes (non-functional genes) that encode additional Hsp90 isoforms that are not expressed as proteins.Ī membrane-associated variant of cytosolic Hsp90, lacking an ATP-binding site, has recently been identified and was named Hsp90N. The five functional human genes encoding Hsp90 protein isoforms are listed below: family The α- and the β-forms are thought to be the result of a gene duplication event that occurred millions of years ago. In mammalian cells, there are two or more genes encoding cytosolic Hsp90 homologues, with the human Hsp90α showing 85% sequence identity to Hsp90β. Yeast Hsp90 is 60% identical to human Hsp90α. Hsp90 is highly conserved and expressed in a variety of different organisms from bacteria to mammals – including the prokaryotic analogue HtpG (high-temperature protein G) with 40% sequence identity and 55% similarity to the human protein. However it was later discovered that Hsp90 also has essential functions in unstressed cells. 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. Whereas cytoplasmic Hsp90 is essential for viability under all conditions in eukaryotes, the bacterial homologue HtpG is dispensable under non-heat stress conditions. Hsp90 is found in bacteria and all branches of eukarya, but it is apparently absent in archaea. A 90 kDa protein is considered fairly large for a non-fibrous protein. The "90" comes from the fact that it has a mass of roughly 90 kilodaltons. Heat shock protein 90 (Hsp90) is one of the most common of the heat-related proteins. 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.
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