Abstract
The neutral histidine-rich polypeptide (HRP) from human parotid secretion was isolated by ion-exchange and gel-filtration chromatography. The complete amino acid sequence determined by automated Edman degradation of the protein, tryptic and Staphylococcus aureus V8 protease peptides, and digestion with carboxypeptidase A is: (Formula: see text) where Pse represents phosphoserine. The polypeptide contains 38 residues and has Mr 4929. The charged amino acids predominate with 7 histidine, 4 arginine, 3 lysine, 3 aspartic acid, 3 glutamic acid residues, and 1 phosphoserine. Assuming minimal charge contributions from histidine and one negative charge from phosphoserine at pH 7, the net charge of HRP is balanced by an equal contribution of basic and acidic residues. Furthermore, the distribution of hydrophilic and hydrophobic residues along the polypeptide chain indicates that there is no structural polarity. The polypeptide lacks threonine, alanine, valine, cysteine, methionine, and isoleucine. HRP did not display sequence similarity with any protein sequence in the National Biomedical Research Foundation Data Bank. HRP is an active inhibitor of hydroxyapatite crystal growth from solutions supersaturated with respect to calcium phosphate salts and therefore must play a role in the stabilization of mineral-solute interactions in oral fluid. In addition, HRP is a potent inhibitor of Candida albicans germination and therefore may be a significant component of the antimicrobial host defense system in the oral cavity.
Highlights
The neutral histidine-rich polypeptide (HRP) from lution dynamics of enamel andexert selectivity on initial human parotid secretion was isolated by ion-exchangbeacterial colonization [1].Human parotid saliva contains a angdel-filtratiocnhromatographyT. he complete group of anionic proteins which exhibit an unexpectedly high adamuegriernauodsaaVtci8oidnporsoeftqtehuaeesnecppereopdteteiitdneer,sm,tiranynepddticdbiygaenSasduttaitoopnmhywaltoietcdhoccEcadurms- anainffitnhietyfoformr haytidornoxoyfatphaetitaecqsuurifraecdeesnaanmdewl hpieclhlicalree implicated [2,3,4,5]
HRP is an active inhibitorof hydroxyapatite crystal growth from solutions supersaturated with respect to calcium phosphate salts and thereforme ust play a role strongly negatively charged amino-terminal segment, the phosphate groups, is important for this process [2]
HRP is similar to the PRPs and statherinby virtue of its high affinity for hydroxyapatite, but differs markedly in amino acid composition in that it contains only 1 residue of in the stabilization of mineral-solute interactions in proline, has a PI of 7.0, and is the smallest known pellicle oral fluid
Summary
HRP is a potent inhibitor of crystal growth (see Table IV and “Results”) which is consistent with its high affinity for hydroxyapatite surfaces [2] Both PRPs and statherin contain 2 phosphoserine residues, and enzymatic removal of the 2 coelutes with statherin from DEAE-Sephadex A-25, but is vicinal phosphate moieties (residues 2 and 3) from the highly almost completely resolved from statherin on Tris-Acryl M- active amino-terminal tryptic hexapeptide of statherin and DEAE The first two attempts primary structure of these cationic peptides has been deterto sequence intact HRP resulted in large carry-overs begin- mined, and all are comprised of amino acid residues, ning at cycle 1 (results not given). The biological activity of HRP differs from that of the aforementioned peptides in that it inhibits C.albicans germination but does not kill in this assay. Forsyth Dental Center, for performing the inhibition of calcium phosphate precipitation and crystal growth assays on HRP, George Crombie for performing amino acid analyses, and Frederica MacMillan for expert technical assistance
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