Background: AgI/II homolog interaction with GP340 is crucial for bacterial attachment to tooth surface. Results: Tandem SRCR domains efficiently adhere/aggregate bacteria. Calcium-induced conformational switch and O-linked carbohydrates of SRCRs are necessary for the interaction with AgI/II homologs. Conclusion: High affinity interactions are dictated by calcium and carbohydrates. Significance: Oral streptococci adhere to specific calcium-induced conformation of immobilized SRCRs and to its carbohydrates. © 2014 by The American Society for Biochemistry and Molecular Biology, Inc.