Oral streptococci such as bind the abundant salivary enzyme -amylase. This interaction may be important in dental plaque formation and metabolism, thus contributing to the initiation and progression of dental caries and periodontal disease, the two most common plaque-mediated diseases. The conjugative transposon Tn was used to insertionally inactivate gene(s) essential to the expression of amylase-binding components of Challis, and a mutant deficient in amylase-binding (Challis Tn1) was identified. While wild-type strains of released both 20 kDa and 82 kDa amylase-binding proteins into culture supernatants, Challis Tn1 expressed the 82 kDa but not the 20 kDa protein. The 20 kDa amylase-binding protein was isolated from culture supernatants of Challis by hydroxyapatite chromatography. A partially purified, functionally active 20 kDa protein was sequenced from blots, and the N-terminal sequence obtained was found to be DEP (A) TDAAT(R)NND. A novel strategy, based on the single-specific-primer polymerase chain reaction technique, enabled the gene inactivated by Tn to be cloned. Analysis of the resultant nucleotide sequence revealed an open reading frame of 585 bp, designated amylase-binding protein A (), encoding a protein of 20 kDa (AbpA), immediately downstream from the insertion site of Tn This protein possessed a potential signal peptide followed by a region having identity with the N-terminal sequence of the 20 kDa amylase-binding protein. These results demonstrate the role of the 20 kDa protein in the binding of amylase to Knowledge of the nature of amylase-binding proteins may provide a better understanding of the role of these proteins in the colonization of in the oral cavity.


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