Cilium Adhesin P216 (MHJ_0493) Is a Target of Ectodomain Shedding and Aminopeptidase Activity on the Surface of Mycoplasma hyopneumoniae

MHJ_0493 (P216) is a highly expressed cilium adhesin in Mycoplasma hyopneumoniae. P216 undergoes cleavage at position 1074 in the S/T-X-F↓-X-D/E-like motif 1072T–N-F↓Q-E1076 generating N-terminal and C-terminal fragments of 120 kDa (P120) and 85 kDa (P85) on the surface of M. hyopneumoniae. Here we show that several S/T-X-F↓X-D/E-like motifs exist in P216 but only 1072T–N-F↓Q-E1076 and 1344I-T-F↓A-D-Y1349 were determined to be bona fide processing sites by identifying semitryptic peptides consistent with cleavage at the phenylalanine residue. The location of S/T-X-F↓-X-D/E-like motifs within or abutting regions of protein disorder greater than 40 consecutive amino acids is consistent with our hypothesis that site access influences the cleavage efficiency. Approximately 20 cleavage fragments of P216 were identified on the surface of M. hyopneumoniae by LC–MS/MS analysis of biotinylated proteins and 2D SDS-PAGE. LC–MS/MS analysis of semitryptic peptides within P216 identified novel cleavage sites. Moreover, detection of a series of overlapping semitryptic peptides that differed by the loss a single amino acid at their N-terminus is consistent with aminopeptidase activity on the surface of M. hyopneumoniae. P120 and P85 and their cleavage fragments bind heparin and cell-surface proteins derived from porcine epithelial-like cells, indicating that P216 cleavage fragments retain the ability to bind glycosaminoglycans.