Abstract
Heat shock protein 90 (HSP90) is an abundant chaperone in the cytosol, including two isoforms α and β. The rat homologue of HSP90 was HSP86, and defined as four domains in this study: N-terminal domain (a.a. 1~237), highly charged linker domain (a.a. 238~272), middle domain (a.a. 273~538) and C-terminal domain (a.a. 539~733). The chaperone activity of HSP90 is modulated by ATP hydrolysis and by interacting with several co-chaperones. In addition, heat-induced transition of HSP90 to self-oligomerization was also necessary for exerting the chaperone activity. Here, we used three HSP86 recombinants (HSP86N a.a. 1~237, HSP86NM a.a 1~538, HSP86C a.a 539~733) to explore the properties of oligomerization in each domain. From suppression assay, oligomerization of HSP86-N and HSP86-C resulted in higher chaperone function, whereas that of HSP86-NM showed lower chaperone function. We assumed that the oligomerization region in the middle domain overlapped with client binding domain. The N-terminal domain has lower critical temperature than the C-terminal domain, suggesting the first step of oligomerization of full length HSP86 starts from N-terminal. The oligomerization of HSP86-N and HSP86-C was affected by factors including ATP, ADP, Ca+ and Zn+, indicating there may be binding site for each factor.