PRB1, PRB2, AND PRB4 CODED POLYMORPHISMS AMONG HUMAN SALIVARY CONCANAVALIN-A BINDING, II-1, AND PO PROLINE-RICH PROTEINS

Six closely linked PRP (proline-rich protein) genes code for many sali vary PRPs that show frequent length and null variants. From determined protein sequences and DNA sequence analysis of variant alleles, we he re report the coding and molecular basis for Con (concanavalin A-bindi ng) and Po (parotid ''o'') protein polymorphisms. The Con1 glycoprotei n is encoded in exon 3 of a PRB2 allele (PRB2L CON1+) with a potential N-linked glycosylation site. Because of a probable gene conversion en compassing greater than or equal to 684 bp of DNA, the ''PRB2-like'' C on2 glycoprotein is encoded in exon 3 of a PRB1 allele (PRB1M CON2+) w ith a potential glycosylation site. The PmF protein is also encoded in the PRB1M CON2+ allele, thus explaining the previously reported assoc iation between Con2 and PmF proteins. A PRB2L CON1- allele contains a single nt missense change [TCT(Ser)-->(C) under bar CT(Pro)] that abol ishes the potential N-linked glycosylation site (NKS-->NKP) in the Con 1 protein, and this explains the Con- type. The Po protein and a glyco protein (II-1) are encoded in the PRB4 gene, and both proteins are abs ent in the presence of a mutation in the PRB4M PO- allele that contain s a single nt change (G-->C) at the +1 invariant position of the intro n 3 5' donor splice site. The genetically determined absence of the II -1 glycoprotein leads to altered in vitro binding of Streptococcus san guis 10556 to salivary proteins, which suggests a biological consequen ce for null mutations of the PRB4 gene.