PRELIMINARY-X-RAY CRYSTALLOGRAPHIC ANALYSIS OF HUMAN SALIVARY CYSTATIN

Human salivary cystatin, a thiol proteinase inhibitor, has been implic ated in potential antimicrobial and antiviral functions of saliva. A v ariant of human salivary cystatin SN expressed and purified in an Esch erichia coli expression system lacking residues 12-16 near the N-termi nus (Delta 12-16) has been crystallized by the vapor-diffusion techniq ue. The crystals are of the hexagonal space group P622 and have cell c onstants of a = 85.41, b = 85.41, c = 131.6 Angstrom, alpha = beta = 9 0, gamma = 120 degrees, and contain two molecules of molecular weight 13 500 per asymmetric unit. The crystals diffract up to a resolution o f 2.2 Angstrom and are suitable for X-ray diffraction analysis.