Subunit asymmetry and roles of conformational switching in the hexameric AAA+ ring of ClpX：（亚基构象转变的不对称和角色hexameric AAA + ClpX环）.pdfVIP

HHS Public Access Author manuscript A Nat Struct Mol Biol . Author manuscript; available in PMC 2015 November 01. u t h Published in final edited form as: o r Nat Struct Mol Biol . 2015 May ; 22(5): 411–416. doi:10.1038/nsmb.3012. M a n u s c Subunit asymmetry and roles of conformational switching in the r i p t hexameric AAA+ ring of ClpX 1 1 1 1,2 Benjamin M. Stinson , Vladimir Baytshtok , Karl R. Schmitz , Tania A. Baker , and Robert T. Sauer1,* 1Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02139 2 A Howard Hughes Medical Institute, Massachusetts Institute of Technology, Cambridge, MA 02139 u t h o Abstract r M a The hexameric AAA+ ring of Escherichia. coli ClpX, an ATP-dependent protein unfolding and n u translocation machine, functions with the ClpP peptidase to degrade target substrates. For efficient s c function, ClpX subunits must switch between nucleotide-loadable (L) and nucleotide-unloadable r i p (U) conformations, but the roles of switching are uncertain. Moreover, it is controversial whether t working AAA+ ring enzymes assume symmetric or asymmetric conformations. Here, we show that a covalent ClpX ring with one subunit locked in the U conformation catalyzes robust ATP- hydrolysis, with each unlocked subunit able to bind and hydrolyze ATP, albeit with highly asymmetric position-specific affinities. Preventing U⇔L interconversion in one subunit alters the cooperativity of ATP hy