Characterization of emb, a gene encoding the major adhesin of Streptococcus defectivus

Streptococcus defectivus is one of the nutritionally variant streptococci, a class of viridans group streptococci first isolated from patients with en docarditis and otitis media. In previous studies, NVS-47, a clinical isolat e of S. defectivus, was shown to bind to the extracellular matrix. A high-m olecular-weight surface protein was identified and proposed to be responsib le for mediating this binding. In the present study, the gene encoding this protein was identified by transposon mutagenesis and characterized. The ge ne (emb) was found to be larger than 14 kb and was partially sequenced. It encodes a protein containing at least 50 repeats of 77 amino acids predicte d to assume an alternating coiled-fail conformation. The domain responsible for extracellular matrix binding was mapped to the N terminus of the prote in. From sequence analysis, Emb is proposed to be the prototype of a new fa mily of streptococcal fibrillar proteins.