PubMed:12379719 JSONTXT

{"project":"FSU-PRGE","denotations":[{"id":"T1","span":{"begin":95,"end":107},"obj":"protein"},{"id":"T2","span":{"begin":124,"end":143},"obj":"protein"},{"id":"T3","span":{"begin":207,"end":215},"obj":"protein"},{"id":"T4","span":{"begin":322,"end":337},"obj":"protein"},{"id":"T5","span":{"begin":379,"end":384},"obj":"protein"},{"id":"T6","span":{"begin":405,"end":410},"obj":"protein"},{"id":"T7","span":{"begin":432,"end":451},"obj":"protein"},{"id":"T8","span":{"begin":536,"end":548},"obj":"protein"},{"id":"T9","span":{"begin":699,"end":711},"obj":"protein"},{"id":"T10","span":{"begin":722,"end":726},"obj":"protein"},{"id":"T11","span":{"begin":731,"end":735},"obj":"protein"},{"id":"T12","span":{"begin":776,"end":781},"obj":"protein"},{"id":"T13","span":{"begin":889,"end":893},"obj":"protein"},{"id":"T14","span":{"begin":929,"end":941},"obj":"protein"},{"id":"T15","span":{"begin":951,"end":955},"obj":"protein"},{"id":"T16","span":{"begin":1000,"end":1005},"obj":"protein"},{"id":"T17","span":{"begin":1107,"end":1111},"obj":"protein"},{"id":"T18","span":{"begin":1171,"end":1176},"obj":"protein"},{"id":"T19","span":{"begin":1340,"end":1344},"obj":"protein"},{"id":"T20","span":{"begin":1475,"end":1479},"obj":"protein"},{"id":"T21","span":{"begin":1484,"end":1488},"obj":"protein"},{"id":"T22","span":{"begin":1605,"end":1609},"obj":"protein"},{"id":"T23","span":{"begin":1665,"end":1669},"obj":"protein"},{"id":"T24","span":{"begin":1673,"end":1677},"obj":"protein"},{"id":"T25","span":{"begin":1755,"end":1759},"obj":"protein"},{"id":"T26","span":{"begin":1902,"end":1906},"obj":"protein"},{"id":"T27","span":{"begin":1910,"end":1914},"obj":"protein"},{"id":"T28","span":{"begin":1932,"end":1936},"obj":"protein"},{"id":"T29","span":{"begin":2462,"end":2466},"obj":"protein"},{"id":"T30","span":{"begin":2518,"end":2522},"obj":"protein"},{"id":"T31","span":{"begin":2527,"end":2531},"obj":"protein"},{"id":"T32","span":{"begin":2669,"end":2674},"obj":"protein"}],"text":"Structural and functional variation within the alanine-rich repetitive domain of streptococcal antigen I/II.\nMembers of the antigen I/II family of cell surface proteins are highly conserved, multifunctional adhesins that mediate interactions of oral streptococci with other oral bacteria, with cell matrix proteins (e.g., type I collagen), and with salivary glycoproteins, e.g., gp340. The interaction of gp340 (formerly designated salivary agglutinin) with Streptococcus mutans requires an alanine-rich repetitive domain (A region) of antigen I/II that is highly conserved in all members of this family of proteins. In this report, we show that the A regions from the two Streptococcus gordonii M5 antigen I/II proteins (SspA and SspB) interact differently with the salivary gp340 glycoprotein and appear to be structurally distinct. Recombinant polypeptides encompassing the A region of SspA or from a highly related S. mutans antigen I/II protein (SpaP) competitively inhibited the interaction of gp340 with intact S. gordonii and S. mutans cells, respectively. In contrast, an A region polypeptide from SspB was inactive, and furthermore, it did not bind to purified gp340 in vitro. Circular dichroism spectra suggested that all three polypeptides were highly alpha-helical and may form coiled-coil structures. However, the A region of SspB underwent a conformational change and exhibited reduced alpha-helical structure at pH 8.5, whereas the A region polypeptides from SspA and SpaP were relatively stable under these conditions. Melt curves also indicated that at physiological pH, the A region of SspB lost alpha-helical structure more rapidly than that of SspA or SpaP when the temperature was increased from 10 to 40 degrees C. Furthermore, the SspB A region polypeptide denatured completely at a temperature that was 7 to 9 degrees C lower than that required for the A region polypeptide of SspA or SpaP. The full-length SspB protein and the three A region peptides migrated in native gel electrophoresis and column chromatography with apparent molecular masses that were approximately 2- to 2.5-fold greater than their predicted molecular masses. However, sedimentation equilibrium ultracentrifugation data showed that the A region peptides sedimented as monomers, suggesting that the peptides may form nonglobular intramolecular coiled-coil structures under the experimental conditions used. Taken together, our results suggest that the A region of SspB is less stable than the corresponding A regions of SspA and SpaP and that this structural difference may explain, at least in part, the functional variation observed in their interactions with salivary gp340."}