Domain structure, expressional regulation and autoimmunity of HSP90

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By use of isoform-specific monoclonal antibodies, the expression of the two HSP90 isoforms was investigated on various rat tissues and osteoclasts and osteoblasts that were induced in alveolar bones of the experimental movement of rat molar teeth. As a result, the predominant and constitutive distribution of HSP90β and stress-induced expression of HSP90α in most murine tissues were demonstrated. We also investigated the domain structure of HtpG, an Esherichia coli homologue of mammalian HSP90 and its domain-domain interactions. HtpG had three major cleavage sites, Arg7-Gly8, Arg336-Glu337 and Lys552-Leu553, susceptible to trypsin. Thus, HtpG consists of three domains: Domain A, Metl-Arg336; Domain B, Glu337-Lys 552; Domain C, Leu553-Ser624. Three kinds of interactions work between the domains of a HtpG dimer: Domain B interacted both with Domain A and Domain C, and moreover, Domain B had a homodimeric interaction. The interaction between Domain B and Domain C was responsible for the dimer conformation of HtpG. Furthermore, Domain B was functionally and structurally divided into two parts: the N-terminal two-third (Glu337-Phe480) that interacted with Domain A and the C-terminal one-third (G1n481-Lys552) that interacted with Domain C. This study first demonstrated the domain structure of HtpG and the interactions between the domains. These characteristics seem to be common among HSP90-family member proteins.