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Publication Abstract from PubMed

The MecA-ClpC complex is a bacterial type II AAA+ molecular machine, responsible for regulated unfolding of substrates, such as transcription factors ComK and ComS, and targeting them to ClpP for degradation. The six subunits of the MecA-ClpC complex form a closed barrel-like structure, featured with three stacked rings and a hollow passage, where substrates are threaded and translocated through successive pores. Although the general concepts of how polypeptides are unfolded and translocated by internal pore loops of AAA+ proteins are long conceived, the detailed mechanistic model remains elusive. With cryo-electron microscopy, we captured four different structures of the MecA-ClpC complexes. These complexes differ in the nucleotide binding states of the two AAA+ rings, and therefore might presumably reflect distinctive, representative snapshots from a dynamic unfolding cycle of this hexameric complex. Structural analysis reveals that nucleotide binding and hydrolysis modulate the hexameric complex in a number of fashions, including the opening of the N-terminal ring, the axial and radial positions of pore loops, the compactness of the C-terminal ring, as well as the relative rotation between the two NBD rings. More importantly, our structural and biochemical data indicate there is an active allosteric communication between the two AAA+ rings, and suggest that concerted actions of two AAA+ rings are required for the efficiency of the substrate unfolding and translocation. These findings provide important mechanistic insights into the dynamic cycle of the MecA-ClpC unfoldase, and especially, lay a foundation toward the complete understanding of the structural dynamics of the general type II AAA+ hexamers.

Structural dynamics of the MecA-ClpC complex: a type II AAA+ protein unfolding machine.,Liu J, Mei Z, Li N, Qi Y, Xu Y, Shi Y, Wang F, Lei J, Gao N J Biol Chem. 2013 Apr 17. PMID:23595989^[2]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.