CLEAVAGE, METHYLATION, AND LOCALIZATION OF THE PSEUDOMONAS-AERUGINOSAEXPORT PROTEINS XCPT, XCPU, XCPV, AND XCPW

Four components of the apparatus of extracellular protein secretion of Pseudomonas aeruginosa, XcPt, -U, -V, and -W (XcpT-W), are synthesize d as precursors with short N-terminal leader peptides that share seque nce similarity with the pilin subunit of this organism. A specialized leader peptidase/methylase, product of the pilD gene, has been shown t o cleave the leader peptide from prepilin and to methylate the N-termi nal phenylalanine of the mature pilin. Antibodies were prepared agains t XcpT-W and used to purify each of these proteins. Sequence analysis of XcpT-W has shown that these proteins, like mature pilin, contain N- methylphenylalanine as the N-terminal amino acid. Analysis of cellular fractions from wild-type and pilD mutant strains of P. aeruginosa sho wed that the precursor forms of XcpT-W are located predominantly in th e bacterial inner membrane, and their localization is not altered afte r PilD-mediated removal of the leader sequence. These studies demonstr ate that the biogenesis of the apparatus of extracellular protein secr etion and that of type IV pili share a requirement for PilD. This bifu nctional enzyme, acting in the inner membrane, cleaves the leader pept ides from precursors of pilins and XcpT-W and subsequently methylates the amino group of the N-terminal phenylalanine of each of its substra tes.