Repeat regions R1 and R2 in the P97 paralogue Mhp271 of Mycoplasma hyopneumoniae bind heparin, fibronectin and porcine cilia

Abstract

Mycoplasma hyopneumoniae, the causative agent of porcine enzootic pneumonia, adheres to ciliated respiratory epithelia resulting in ciliostasis and epithelial cell death. The cilium adhesin P97 (Mhp183) contains two repeat regions, designated R1 and R2, that play key roles in adherence. Eight pentapeptide repeats in R1 are sufficient to bind porcine cilia; however, both R1 and R2 are needed to bind heparin. Mhp271, a paralogue of P97, is the only other M. hyopneumoniae protein to contain both R1 and R2 repeats. These repeats are arranged as a set of three pentapeptide repeats (designated R1A₂₇₁), two decapeptide repeats (designated R2₂₇₁), and a second set of six pentapeptide repeats (designated R1B₂₇₁). To determine their function, recombinant proteins containing R1A₂₇₁) (F1₂₇₁) and R2₂₇₁-R1B₂₇₁ (F2₂₇₁) were constructed and used in in vitro binding assays. F2₂₇₁, but not F1₂₇₁, bound heparin (K(D)=8.1 ± 0.4 nM), fibronectin (K(D)=174 ± 13 nM) and porcine cilia. Pre-incubation of F2₂₇₁ with 100 µM heparin blocked cilium binding by ~69%. Cell surface shaving with trypsin combined with two-dimensional liquid chromatography coupled to tandem mass spectrometry analysis identified Mhp271 as surface-exposed. Our data suggest that both R1 and R2 in Mhp271 are involved in binding to host molecules.