The MBA proteins of ureaplasmas appear to be particularly analogous to the Vsa proteins because of the size variation that results from gain or loss of tandem repeats and the phase variation that results from DNA inversion (Zimmerman et al., 2011). Proteins that undergo extensive size variation because of gain or loss of tandem repeats has been described for other pathogenic species of Mycoplasma including M. agalactiae, M. arthritidis, M. bovis, M. hominis, and M. hyorhinis (Yogev et al., 1991; Lysnyansky et al., 1996; Zhang Natural Product Library datasheet & Wise, 1996; Ladefoged, 2000; Tu et al., 2005; Nouvel et al., 2009), but the
pathogenic significance and effect on cytoadherence of protein size variation in these species have
for the most part not been studied. Mycoplasmas producing a long Vsa protein have been shown in previous Ribociclib chemical structure studies to be shielded from the lytic effects of complement and to have a markedly reduced ability to form a biofilm on glass and plastic surfaces (Simmons & Dybvig, 2003; Simmons et al., 2004, 2007). We extend these findings in this study to include cytoadherence. Independent of the Vsa isotype, mycoplasmas producing a long Vsa protein adhered less efficiently to epithelial cells than did mycoplasmas producing a short Vsa protein. We also found that the EPS-I polysaccharide is required for full cytoadherence. The mutants that lack the polysaccharide exhibited extremely poor adherence to MLE-12 cells, despite the fact that these mutants adhere robustly to abiotic surfaces and efficiently colonize mice in vivo (Daubenspeck et al., 2009). Cytoadherence in this system may be complex. Although it is possible that EPS-I, which is composed of glucose and galactose, serves as an adhesin, the addition of the pertinent monosaccharides galactose and glucose or the disaccharide lactose to binding
assays failed to inhibit the adherence of M. pulmonis to erythrocytes (Minion et al., 1984). Nevertheless, EPS-I may be required for an initial mafosfamide interaction that brings the mycoplasma into close contact with host cells. The adhesins that are responsible for cytoadherence may be partially buried within the Vsa shield when the Vsa proteins are long. These adhesins would be exposed leading to efficient adherence when the Vsa proteins are short. This suggested process for adherence of the mycoplasma to host cells is reminiscent of a model proposed by Minion et al. (1984). Because of the high frequency of Vsa size variation that occurs during growth of the mycoplasma (Simmons et al., 2007), varied subpopulations of mycoplasmas would be present throughout the infection with some cells more adherent than others. The presence of the adherent population would be needed for colonization. The nonadherent population might better resist interactions with macrophages and other cells of the host immune system.