Immunodominant proteins P1 and P40/P90 from human pathogen Mycoplasma pneumoniae

Mycoplasma pneumoniae is a bacterial human pathogen that causes primary atypical pneumonia. M. pneumoniae motility and infectivity are mediated by the immunodominant proteins P1 and P40/P90, which form a transmembrane adhesion complex. Here we report the structure of P1, determined by X-ray crystallography and cryo-electron microscopy, and the X-ray structure of P40/P90. Contrary to what had been suggested, the binding site for sialic acid was found in P40/P90 and not in P1. Genetic and clinical variability concentrates on the N-terminal domain surfaces of P1 and P40/P90. Polyclonal antibodies generated against the mostly conserved C-terminal domain of P1 inhibited adhesion of M. pneumoniae , and serology assays with sera from infected patients were positive when tested against this C-terminal domain. P40/P90 also showed strong reactivity against human infected sera. The architectural elements determined for P1 and P40/P90 open new possibilities in vaccine development against M. pneumoniae infections. Adhesion of the human pathogen Mycoplasma pneumoniae to pulmonary epithelial cells is mediated by a transmembrane complex composed of proteins P1 and P40/P90. Here, the authors present the structures of M. pneumoniae P1 and P40/P90, show that P40/P90 binds sialylated oligosaccharides and have also determined the crystal structures of P40/P90 complexes with 3’-Sialyllactose and 6’-Sialyllactose, which provide insights into the mechanisms of adhesion and gliding on host cell surfaces.