Mutations in the fifth-position glutamate in Pseudomonas aeruginosa pilin affect the transmethylation of the N-terminal phenylalanine.
The pili of Pseudomonas aeruginosa are composed of 15-kDa pilin monomers that are synthesized in the cytoplasm and assembled in the membrane. Processing occurs between the synthesis and assembly steps. The propilin is cleaved by a unique leader peptidase encoded by pilD, which is adjacent to the pilin structural gene pilA. This generates an N-terminal phenylalanine that is subsequently methylated by an as yet uncharacterized transmethylase. The pili of P. aeruginosa belong to the type IV class of pilins, which share a highly conserved N-terminal region 35 amino acids in length, containing a short leader of 6 or 7 amino acids. Two site-specific mutants in the N-terminal region of the mature pilin were constructed. Reestablishing the fifth-position glutamate in a four amino acid deletion mutant (amino acids 4-7) restored the leader peptidase cleavage but not the methylation. A mutation of the fifth-position glutamate to alanine decreased the degree of methylation of the N-terminal phenylalanine. Pili were not assembled by these mutants as assessed by electron microscopy and sensitivity to pilus-specific bacteriophage. Methylation may be required for recognition of the pilin by the assembly machinery and is not residue specific. The fifth-position glutamate appears to play an important role in transmethylase recognition of the pilin subunit.
Macdonald
D L
DL
Department of Microbiology, University of Alberta, Edmonton, Canada.
Pasloske
B L
BL
Paranchych
W
W
D000595:Amino Acid Sequence; D001425:Bacterial Outer Membrane Proteins / Q000235:genetics*; D001483:Base Sequence; D004252:DNA Mutational Analysis; D010450:Endopeptidases / Q000378:metabolism*; D036781:Fimbriae Proteins; D008565:Membrane Proteins; D008969:Molecular Sequence Data; D009154:Mutation; D010649:Phenylalanine / Q000378:metabolism; D011496:Protein Methyltransferases / Q000378:metabolism*; D011499:Protein Processing, Post-Translational; D011550:Pseudomonas aeruginosa / Q000235:genetics*; D017386:Sequence Homology, Amino Acid; D012697:Serine Endopeptidases; D013379:Substrate Specificity
D001425:Bacterial Outer Membrane Proteins; D008565:Membrane Proteins; D036781:Fimbriae Proteins; D010649:Phenylalanine; D011496:Protein Methyltransferases; D010450:Endopeptidases; D012697:Serine Endopeptidases; C026515:type I signal peptidase