Sequence TTKF ↓ QE defines the site of proteolytic cleavage in Mhp683 protein, a novel glycosaminoglycan and cilium adhesin of Mycoplasma hyopneumoniae

Mycoplasma hyopneumoniae colonizes the ciliated respiratory epithelium of swine, disrupting mucociliary function and inducing chronic inflammation. P97 and P102 family members are major surface proteins of M. hyopneumoniae and play key roles in colonizing cilia via interactions with glycosaminoglycans and mucin. The p102 paralog, mhp683, and homologs in strains from different geographic origins encode a 135-kDa preprotein (P135) that is cleaved into three fragments identified here as P45 683, P48 683, and P50 683. A peptide sequence (TTKF ↓ QE) was identified surrounding both cleavage sites in Mhp683. N-terminal sequences of P48 683 and P50 683, determined by Edman degradation and mass spectrometry, confirmed cleavage after the phenylalanine residue. A similar proteolytic cleavage site was identified by mass spectrometry in another paralog of the P97/P102 family. Trypsin digestion and surface biotinylation studies showed that P45 683, P48 683, and P50 683 reside on the M. hyopneumoniae cell surface. Binding assays of recombinant proteins F1 683-F5 683, spanning Mhp683, showed saturable and dose-dependent binding to biotinylated heparin that was inhibited by unlabeled heparin, fucoidan, and mucin. F1 683-F5 683 also bound porcine epithelial cilia, and antisera to F2 683 and F5 683 significantly inhibited cilium binding by M. hyopneumoniae cells. These data suggest that P45 683, P48 683, and P50 683 each display cilium- and proteoglycan-binding sites. Mhp683 is the first characterized glycosaminoglycan-binding member of the P102 family. © 2011 by The American Society for Biochemistry and Molecular Biology, Inc.