Molecular mechanisms of substrate degradation by the 26S proteasome revealed by CryoEM (952.6)

Abstract

The 26S proteasome is the major eukaryotic ATP‐dependent protease, responsible for regulating the proteome through degradation of ubiquitin‐tagged substrates. The proteasome regulatory particle, containing the heterohexameric AAA+ ATPase motor and the essential deubiquitinase Rpn11, recognizes substrates, removes their ubiquitin chains, and translocates them into the associated peptidase after unfolding. Despite recent insights into the architecture of the regulatory particle, little is known about the structural requirements and mechanisms for substrate processing. Here, we present the first structure of the 26S proteasome during substrate degradation and show that it switches from a pre‐engaged to a translocation‐competent conformation. This conformation is characterized by a rearranged ATPase ring with uniform subunit interfaces, a widened central channel coaxially aligned with the peptidase, and a spiral orientation of pore loops that suggests a rapid progression of ATP‐hydrolysis events around the ring. Importantly, Rpn11 moves from an occluded position to directly above the central pore, facilitating substrate deubiquitination concomitant with translocation.Grant Funding Source: Supported by NIH grant R01‐GM094497‐01A1, ACS grant 121453‐PF‐11‐178‐01‐TBE