title: A sialoreceptor binding motif in the Mycoplasma synoviae adhesin VlhA.
abstract: Mycoplasma synoviae depends on its adhesin VlhA to mediate cytadherence to sialylated host cell receptors. Allelic variants of VlhA arise through recombination between an assemblage of promoterless vlhA pseudogenes and a single transcription promoter site, creating lineages of M. synoviae that each express a different vlhA allele. The predicted full-length VlhA sequences adjacent to the promoter of nine lineages of M. synoviae varying in avidity of cytadherence were aligned with that of the reference strain MS53 and with a 60-a.a. hemagglutinating VlhA C-terminal fragment from a Tunisian lineage of strain WVU1853(T). Seven different sequence variants of an imperfectly conserved, single-copy, 12-a.a. candidate cytadherence motif were evident amid the flanking variable residues of the 11 total sequences examined. The motif was predicted to adopt a short hairpin structure in a low-complexity region near the C-terminus of VlhA. Biotinylated synthetic oligopeptides representing four selected variants of the 12-a.a. motif, with the whole synthesized 60-a.a. fragment as a positive control, differed (P<0.01) in the extent they bound to chicken erythrocyte membranes. All bound to a greater extent (P<0.01) than scrambled or irrelevant VlhA domain negative control peptides did. Experimentally introduced branched-chain amino acid (BCAA) substitutions Val3Ile and Leu7Ile did not significantly alter binding, whereas fold-destabilizing substitutions Thr4Gly and Ala9Gly tended to reduce it (P<0.05). Binding was also reduced to background levels (P<0.01) when the peptides were exposed to desialylated membranes, or were pre-saturated with free sialic acid before exposure to untreated membranes. From this evidence we conclude that the motif P-X-(BCAA)-X-F-X-(BCAA)-X-A-K-X-G binds sialic acid and likely mediates VlhA-dependent M. synoviae attachment to host cells. This conserved mechanism retains the potential for fine-scale rheostasis in binding avidity, which could be a general characteristic of pathogens that depend on analogous systems of antigenically variable adhesins. The motif may be useful to identify previously unrecognized adhesins.
authors.affiliation: Department of Biomedical Sciences, College of Osteopathic Medicine, University of New England, Biddeford, Maine, United States of America.
authors.forename: Meghan
authors.initials: M
authors.lastname: May
authors.affiliation: Department of Biological Sciences, Jess and Mildred Fisher College of Science and Mathematics, Towson University, Towson, Maryland, United States of America.
authors.forename: Dylan W
authors.initials: DW
authors.lastname: Dunne
authors.affiliation: Department of Infectious Diseases and Pathology, College of Veterinary Medicine, University of Florida, Gainesville, Florida, United States of America.
authors.forename: Daniel R
authors.initials: DR
authors.lastname: Brown
mesh_terms: D000483:Alleles; D020816:Amino Acid Motifs; D000818:Animals; D001422:Bacterial Adhesion; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D019921:Biotinylation; D002645:Chickens; D004912:Erythrocytes / Q000737:chemistry* / Q000187:drug effects / Q000378:metabolism / Q000382:microbiology; D015870:Gene Expression; D006388:Hemagglutinins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D037102:Lectins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D045805:Mycoplasma synoviae / Q000737:chemistry* / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D009842:Oligopeptides / Q000737:chemistry / Q000378:metabolism; D011485:Protein Binding; D017510:Protein Folding; D017433:Protein Structure, Secondary; D011544:Pseudogenes; D011956:Receptors, Cell Surface / Q000737:chemistry* / Q000378:metabolism; D012794:Sialic Acids / Q000494:pharmacology; D012795:Sialoglycoproteins / Q000737:chemistry* / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D006388:Hemagglutinins; D037102:Lectins; D009842:Oligopeptides; D011956:Receptors, Cell Surface; D012794:Sialic Acids; D012795:Sialoglycoproteins; C406455:VlhA protein, Mycoplasma synoviae