Synthesis of lectin-like protein adhesive molecules is a favored method by which oral bacteria adhere to hard and soft oral surfaces or other bacteria already adhering to these surfaces. The evolutionary origin of adhesin molecules is unknown. Prevotella loescheii, a Gram negative bacteroide-like inhabitant of the oral cavity synthesizes a 75 kDa protein adhesin that recognizes galactosyl moieties. The adhesin has been isolated and characterized biochemically and the gene encoding the protein has been cloned and sequenced. Its gene is one of only two known examples in which a stretch of DNA sequence is not read at the level of transcription; this is the hallmark of a rare ribosomal """"""""frameshifting hop"""""""". A 213 residue sequence extending from amino acid 318 to 531 shows significant homology to the Escherichia coli enzyme, beta- galactosidase. Recent studies have shown that P. loescheii synthesizes its own inducible beta-galactosidase when grown at the expense of lactose. This observation raises the possibility that part of the adhesin, including its binding domain, was derived from the enzyme. If this supposition is correct, then the degree of amino acid homology between the adhesin and the P. loescheii b- galactosidase should be greater than that of the enteric enzyme. The bacteroide beta-galactosidase is currently being purified by conventional chromatographic techniques for the purpose of characterizing its properties and determining terminal amino acid sequence. This information will be used to clone and sequence the gene so that the amino acid sequence can be deduced for comparison with the adhesin. The gene of P. loescheii enzyme; enolase, has been cloned and sequenced because a fraction of the total amount synthesized was found on the surface of the cell. The enzyme is currently being purified and characterized to determine if two different isoforms of the protein exist.
