Invited Review: Genetics of Human Salivary Proteins

A potent inhibitor of human leukocyte elastase (EC 3.4.21.37) and cathepsin G (EC 3.4.21.20) and of human trypsin (EC 3.4.21.4) has been purified from human parotid secretions. The complete amino acid sequence of this protein has been determined. The sequence suggests that the protein has two domains of about 54 amino acids, each of which contains four disulfide bonds. On the basis of a limited homology to other protease inhibitors, the antielastase and antitrypsin activities are thought to be properties of the C-terminal and N-terminal domains, respectively. The affinity of the inhibitor for leukocyte elastase is very high, suggesting a functional role for the protein in preventing elastase-mediated damage to oral and possibly other mucosal tissues.

The amino acid sequence of human gamma-trace, a basic microprotein without known function, was determined by automated Edman degradations of the carboxymethylated polypeptide chain and of fragments obtained by cyanogen bromide treatment and tryptic digestion after blocking of lysine residues. The single polypeptide chain contained 120 residues, and the calculated Mr was 13,260. A proline residue at position 3 was partly hydroxylated. The presence of gamma-trace in a significant proportion of the cells in the anterior lobe of simian and human pituitary glands was demonstrated by immunohistochemical procedures with a rabbit antiserum against human gamma-trace. The tissue localization and amino acid sequence of gamma-trace indicated that this protein is connected with the peptidergic gastroenteropancreatic neuroendocrine system.