HSP90: Molecular Weight

The HSP90 family represents a group of well-conserved proteins with an average molecular mass of 90 kDa.  There are two major cytosolic Hsp90 isoforms, the inducible Hsp90α1 (HspC1) and the constitutive Hsp90β (HspC3), commonly termed Hsp90 ^1,26.  Hsp90 is the major soluble protein of the cell and most commonly located in the cytoplasm. Like many other chaperones, Hsp90 is a rather hydrophobic protein whose hydrophobicity further increases after heat shock ^32,33. The HSP90 family members are encoded by a multigene family encompassing six genes and 11 pseudogenes in humans ²⁶. Functional genes encoding HSP90 proteins map to human chromosomes 6, 11, 12, 14, and 16 ²⁶. The most studied genes are HSP90AA1 (HSPC1) and HSP90AB1 (HSPC3) encoding proteins that differ by eight amino acids. While Hsp90α1 (HspC1) represents the stress-inducible isoform, Hsp90β (HspC3) is a constitutively expressed protein. The genes are clustered on chromosome 14q32.32 and 6p12, respectively. Two transcript variants encoding different isoforms have been found for the HSP90A gene.