Structural highlights
FunctionPAC_STRMG Surface protein antigen implicated in dental caries. Publication Abstract from PubMedThe Streptococcus mutans Antigen I/II (AgI/II) is a cell surface localized protein that adheres to salivary components and extracellular matrix molecules. Here we report the 2.5 A resolution crystal structure of the complete carboxy-terminal (C-terminal) region of AgI/II. The C-terminal region is comprised of three major domains: C1, C2, and C3. Each domain adopts a DE-variant IgG fold, with two beta-sheets whose A and F strands are linked through an intramolecular isopeptide bond. The adherence of the C-terminal AgI/II fragments to the putative tooth surface receptor salivary agglutinin (SAG), as monitored by surface plasmon resonance, indicated that the minimal region of binding was contained within the first and second DE-variant-IgG domains (C1 and C2) of the C-terminus. The minimal C-teriminal region that could inhibit Streptococcus mutans adherence to SAG was also confirmed to be within the C1 and C2 domains. Competition experiments demonstrated that the C- and N-terminal regions of AgI/II adhere to distinct sites on SAG. A cleft formed at the intersection between these C1 and C2 domains bound glucose molecules from the cryo-protectant solution, revealing a putative binding site for its highly glycosylated receptor SAG. Finally, electron microscopy images confirmed the elongated structure of AgI/II and enabled building a composite tertiary model that encompasses its two distinct binding regions. Crystal structure of the C-terminus of Streptococcus mutans antigen I/II and characterization of salivary agglutinin adherence domains.,Larson MR, Rajashankar KR, Crowley PJ, Kelly C, Mitchell TJ, Brady LJ, Deivanayagam C J Biol Chem. 2011 Apr 19. PMID:21505225[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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