Fig. 8: Model of CpaF catalysis coupled to Tad pilus assembly.
From: Conformational changes in the motor ATPase CpaF facilitate a rotary mechanism of Tad pilus assembly
(top) Schematic of the C. crescentus Tad pilus machinery and (bottom) the rotary model of CpaF catalysis. ATP binding and hydrolysis rotates the C2 axis, and thus the platform protein complex, clockwise by 60°, converting CpaF from the compact to the expanded state. In this AlphaFold predicted conformation, CpaG and CpaH are positioned to facilitate pilin entry into the platform pore. Upon subsequent ADP release by CpaF and its transition to the compact state, the contracting mechanical forces are predicted to incorporate the pilins into the filament (PDB: 8U1K). Rounds of CpaF catalysis facilitate pilus assembly, which exits the outer membrane via the CpaC-CpaO secretin complex. The cryo-EM structure of the Tad secretin was determined from Pseudomonas aeruginosa (PDB: 8ODN).
