CryoEM map ofPseudomonas aeruginosaPilQ enables structural characterization of TsaP

Abstract

19The type IV pilus machinery is a multi-protein complex that polymerizes and 20 depolymerizes a pilus fibre used for attachment, twitching motility, phage adsorption, natural 21 competence, protein secretion, and surface-sensing. An outer membrane secretin pore is required 22 for passage of the pilus fibre out of the cell. Herein, the structure of the tetradecameric secretin, 23PilQ, from the Pseudomonas aeruginosa type IVa pilus was determined to 4.3 Å resolution in the 24 presence and absence of C7 symmetric spokes. The heptameric spokes were found to be the two 25 tandem C-terminal domains of TsaP. TsaP forms a belt around PilQ and while the protein is not 26 essential for PilQ assembly, over-expression of TsaP triggers the surface-sensing signal cascade 27 upstream of PilY1, leading to cyclic di-GMP up-regulation. These results resolve the identity of 28 the spokes identified with Proteobacterial PilQ and may reveal a new component of the surface-29 sensing cyclic di-GMP signal cascade. 30 31

CryoEM structure of the outer membrane secretin channel pIV from the f1 filamentous bacteriophage

“…The other hydrophobic girdle (located half way down the barrel) would then lie within the periplasm, in a similar position to where pilotins are seen to bind to other secretins (Supplementary Fig. 10) 53 . The fact that this hydrophobic girdle has been evolutionarily maintained in f1pIV, even in the absence of a phage pilotin, highlights its functional importance.…”