title: Structural dynamics of the MecA-ClpC complex: a type II AAA+ protein unfolding machine.
abstract: 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 have long been conceived, the detailed mechanistic model remains elusive. With cryoelectron 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 ways, 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 nucleotide-binding domain 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 the 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.
authors.affiliation: Ministry of Education Key Laboratory of Protein Sciences, Center for Structural Biology, School of Life Sciences, Tsinghua University, Beijing 100084, China.
authors.forename: Jing
authors.initials: J
authors.lastname: Liu
authors.forename: Ziqing
authors.initials: Z
authors.lastname: Mei
authors.forename: Ningning
authors.initials: N
authors.lastname: Li
authors.forename: Yutao
authors.initials: Y
authors.lastname: Qi
authors.forename: Yanji
authors.initials: Y
authors.lastname: Xu
authors.forename: Yigong
authors.initials: Y
authors.lastname: Shi
authors.forename: Feng
authors.initials: F
authors.lastname: Wang
authors.forename: Jianlin
authors.initials: J
authors.lastname: Lei
authors.forename: Ning
authors.initials: N
authors.lastname: Gao
mesh_terms: D000255:Adenosine Triphosphate / Q000737:chemistry; D000494:Allosteric Regulation; D019943:Amino Acid Substitution; D001412:Bacillus subtilis / Q000201:enzymology*; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000648:ultrastructure*; D001665:Binding Sites; D020285:Cryoelectron Microscopy; D006360:Heat-Shock Proteins / Q000737:chemistry / Q000235:genetics / Q000648:ultrastructure*; D006868:Hydrolysis; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D011485:Protein Binding; D054730:Protein Interaction Domains and Motifs; D020836:Protein Structure, Quaternary; D058767:Protein Unfolding
chemical_list: D001426:Bacterial Proteins; C087481:ClpC protein, Bacteria; D006360:Heat-Shock Proteins; C083616:mecA protein, Bacillus subtilis; D000255:Adenosine Triphosphate
keywords: AAA+ Hexamers; ATP-dependent Protease; ATPases; ClpC; Electron Microscopy (EM); HSP100; MecA; Protein Degradation; Protein Structure; Protein Unfolding Machine