Primary Structure and Anticandidal Activity of the Major Histatin from Parotid Secretion of the Subhuman Primate, Macaca fascicularis

Abstract

A major macaque histatin (M-histatin 1) from the parotid secretion of the subhuman primate, Macaca fascicularis, was isolated by gel filtration on Bio-Gel P-2 and purified to homogeneity by reversed-phase high-performance liquid chromatography on a TSK-ODS C₁₈ column. The complete amino acid sequence of M-histatin 1, determined by automated Edman degradation, is: 1 10 20 Asp-Pse-His-Glu-Glu-Arg-His-His-Gly-Arg-His-Gly-His-His-Lys-Tyr-Gly-Arg-Lys-Phe 21 30 38 His-Glu-Lys-His-His-Ser-His-Arg-Gly-Tyr-Arg-Ser-Asn-Tyr-Leu-Tyr-Asp-Asn M-histatin 1 contains 38 amino acid residues, a phosphoserine at residue 2, has a molecular weight of 4881.8, a calculated pI of 8.5, and histidine forms 26.3% of the mass. The hydropathicity plot of M-histatin 1 predicts that the molecule is entirely hydrophilic, and Chou-Fasman secondary prediction indicates that the polypeptide is devoid of alpha-helix and beta-sheet conformation in aqueous solutions but contains a series of beta turns. M-histatin 1 includes a six-amino-acid insert (residue 10-15) not present in human histatins and, with the introduction of gaps to maximize homology, it displays 89% and 91% sequence similarity with human histatins 1 and 3, respectively. M-histatin 1 exhibited fungicidal and fungistatic effects against the dimorphic pathogen, Candida albicans, in three separate bioassays. Its anticandidal effects were comparable with or greater than those of human histatins 1, 3, and 5. M-histatins 2, 3, and 4 were not sequenced directly because insufficient materials were available, but the amino acid composition of M-histatin 3 was nearly identical to that of the N-terminal 20 amino acid residues of M-histatin 1. There appears to be only one major histatin in macaque parotid secretion in contrast to the family of histatins in human parotid and submandibular secretions, and the significance of this in the context of evolution and mechanism of action in anticandidal assays is discussed.