title: Structural insights into the Type II secretion nanomachine.
abstract: The Type II secretion nanomachine transports folded proteins across the outer membrane of Gram-negative bacteria. Recent X-ray crystallography, electron microscopy, and molecular modeling studies provide structural insights into three functionally and spatially connected units of this nanomachine: the cytoplasmic and inner membrane energy-harvesting complex, the periplasmic helical pseudopilus, and the outer membrane secretin. Key advances include cryo-EM reconstruction of the secretin and demonstration that it interacts with both secreted substrates and a crucial transmembrane clamp protein, plus a biochemical and structural explanation of the role of low-abundance pseudopilins in initiating pseudopilus growth. Combining structures and protein interactions, we synthesize a 3D view of the complete complex consistent with a stepwise pathway in which secretin oligomerization defines sites of nanomachine biogenesis.
authors.affiliation: Department of Bacteriology, University of Wisconsin-Madison, Madison, WI, USA.
authors.forename: Lorraine S
authors.initials: LS
authors.lastname: McLaughlin
authors.forename: Rembrandt J F
authors.initials: RJ
authors.lastname: Haft
authors.forename: Katrina T
authors.initials: KT
authors.lastname: Forest
mesh_terms: D057055:Aspartic Acid Proteases / Q000378:metabolism; D021961:Cell Membrane Structures / Q000737:chemistry; D036781:Fimbriae Proteins / Q000737:chemistry / Q000378:metabolism; D008958:Models, Molecular; D049329:Nanostructures / Q000737:chemistry*
chemical_list: D036781:Fimbriae Proteins; D057055:Aspartic Acid Proteases