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. Author manuscript; available in PMC: 2008 Dec 1.
Published in final edited form as: Curr Opin Microbiol. 2007 Nov 5;10(6):624–629. doi: 10.1016/j.mib.2007.09.012

Fig 2.

Fig 2

A model for the switching of polarity of Type IV pilus. A superstructure including PilB, PilT, PilC is present at both leading pole and lagging pole. The lipoprotein Tgl is only present at the leading pole and this causes the secretin PilQ to be disassembled at the lagging pole and assembled at the leading pole. The presence of PilQ channels allows the assembly of PilA filaments, from pre-pilin monomers (Pre-PilA), at the leading pole. Also PilB participates in the assembly of PilA by hydrolyzing ATP (A). During S-motility the retraction of TFP allows the cell to move forward. Disassembly of PilA filaments for TFP retraction is mediated by the ATPase activity of PilT (B). When the signal for a reversal occurs, Tgl molecules synthesized ex novo and/or taken from the external environment allow the formation of an active machinery at the new leading pole (C).