Binding mechanism between Hsp90 and Sgt1 explored by homology modeling and molecular dynamics simulations in rice

The Hsp90 (for heat shock protein90) and the Sgt1 (for suppressor of the G2 allele of skp1) are widely distributed in animals, yeast, and plants. The former functions as molecular chaperon activating a series of client proteins, the latter functions as an adaptor protein participating in multiple biological processes such as immunity response through interactions with different protein complexes. In the present study, we have constructed a homology model of Hsp90-Sgt1 complex in rice based on a recently resolved structure from barley and Arabidopsis to explore its binding mechanisms and to understand the detailed interaction profile. A total of 20 ns explicit solvent molecular dynamics simulations combined with MM-GBSA computations and virtual alanine scanning were performed for the modeled complex. In the final structure, three strong salt bridges were found between OsHsp90 and OsSgt1, D217(OsHsp90)-K186(OsSgt1), D218(OsHsp90)-K237(OsSgt1) and K161(OsHsp90)-E239(OsSgt1). Besides, residue Y173 of OsSgt1 played a vital role in the interactions with OsHsp90, the detailed interactions were discussed. These results would help us understand the critical features determining the Hsp90-Sgt1 binding process.