Cloning and Sequence Analysis of a Protective M-like Protein Gene fromStreptococcus equisubsp.zooepidemicus

Streptococcus equisubsp.zooepidemicus, a Lancefield group C streptococcus, is a frequently isolated oppor- tunistpathogenfromavarietyofanimalhosts,includingthehorse.Previousstudieshaveindicatedthatequine strains carry antigens with characteristics of the antiphagocytic M proteins on the Lancefield groups A and G streptococci. We have cloned a protective M-like protein gene (SzPW60) of an equine strain ofS. equisubsp. zooepidemicusW60 and determined its sequence. This gene encodes a protein with a molecular weight of 40,123 which protects mice against subsp. zooepidemicus but not subsp. equi, stimulates antibodies which opsonize subsp.zooepidemicusbut notequi, and reacts with antiserum to the protein of the parent strain. The predicted amino acid structure shows significant homology with the carboxy termini of groups A and G M proteins but nootherhomology.TheM-likeprotein,althoughshowinganextensiveregionofalphahelix,lackstheA,B,and CrepeatsfoundingroupAMproteinsandhasashortersignalsequence.Aproline-richregionupstreamfrom the LPSTGE motif contains 20 repeats of the tetrapeptide PEPK. The presence of this repeat region may account for the slow migration of the M-like protein in sodium dodecyl sulfate-polyacrylamide gel electro- phoresis. Streptococcus equisubsp.zooepidemicus, a Lancefield group C streptococcus, is the most frequently isolated opportunist pathogen of horses. A normal mucosal commensal, it causes purulent respiratory infections of weanling and yearling horses anduterineinfectionsinelderlymares.Italsocausesdiseasein a variety of other animal hosts.