Abstract
SGT1 and RAR1 are highly conserved eukaryotic proteins that interact with HSP90, a molecular chaperone. In plants, SGT1, RAR1 and HSP90 are essential for disease resistance triggered by a number of resistance (R) proteins. SGT1 and HSP90 also play a crucial role in Nod-like receptors (NLRs)-mediated innate immunity responses in mammals. Here we present structural and functional characterization of plant RAR1-SGT1-HSP90 complex. Crystal structure analysis and NMR-based interaction surface mapping of CS domain of SGT1 and N-terminal domain of HSP90 together with mutational analyses showed that the CHORD-II domain of RAR1 and the N-terminal domain of HSP90 interact with opposite sides of the CS domain. Functional analysis of the CS mutations indicated that the interaction between SGT1 and HSP90 is required for disease resistance triggered by Rx, a potato R protein. Biochemical reconstitution experiments revealed that RAR1 functions to enhance SGT1-HSP90 interaction by promoting ternary complex formation.
