Two coding change mutations in the HIS2(2) allele characterize the salivary histatin 3-2 protein variant

The decoded amino acid sequence of a salivary protein variant, histatin 3-2 (formerly termed Pb c), that is found primarily and in high frequency in Black populations was determined by genomic PCR and direct sequencing of the HIS2(2) allele. Two different mutations that cause coding changes were found in exon 5. The first mutation is a single nucleotide (T-->A) substitution that causes a TAT (Tyr)-->TAA (Stop) change at residue 28. This premature stop mutation results in a 27 amino acid histatin 3-2 protein, which is 5 amino acids smaller than the common histatin 3-1 allelic protein (a product of the HIS2(1) allele). The second mutation, a single nucleotide (G-->A) substitution (located only 19 nucleotides upstream of the first mutation) causes a CGA (Arg)-->CAA (Gln) change at residue 22, which eliminates a proteolytic cleavage site. These two mutations explain the differences in electrophoretic patterns of HIS2(1) versus HIS2(2) coded histatin peptides and may have functional significance. Each mutation alters a different DNA restriction site, and this provides a DNA-based test for the mutations. This test should greatly simplify population and family studies of this protein polymorphism, since the saliva-based test is considerably more problematic. Elucidation here of the derived protein sequence of the variant histatin 3-2 protein may also facilitate functional studies.