Characterization of LppS, an adhesin of Mycoplasma conjunctivae

A serine-rich membrane protein named LppS from Mycoplasma conjunctivae, the aetiological agent of infectious keratoconjunctivitis (IKC) of domestic and wild Caprinae, was characterized. Gene cloning and sequence analysis of the lppS gene revealed that it encoded a membrane protein precursor. The protein had a typical signal sequence and a signal peptidase II cleavage site followed by a cysteine residue representing a potential acylation site. The mature LppS protein had an apparent molecular mass of 150 kDa and was found in the detergent-associated fraction of Tween 20 extracted M. conjunctivae proteins. It possessed a serine-rich domain of 41 aa with 37 (90.2 %) serine residues. Twenty-seven of these serine residues were contiguous. The protein adhered to lamb joint synovial cells. Using an in vitro adhesion model, Fab fragments from IgG directed against recombinant purified LppS were shown to specifically inhibit adhesion of M. conjunctivae to lamb cells. Thus, LppS is likely to be an adhesin of M. conjunctivae that may play an important role in the pathogenesis of IKC.