Preliminary X-ray crystallographic analysis of human salivary cystatin

Human salivary cystatin, a thiol proteinase inhibitor, has been implicated in potential antimicrobial and antiviral functions of saliva. A variant of human salivary cystatin SN expressed and purified in an Escherichia coil expression system lacking residues 12-16 near the N-terminus (Δ12-16) has been crystallized by the vapor-diffusion technique. The crystals are of the hexagonal space group P622 and have cell constants of a = 85.41, b = 85.41, c = 131.6 Å, α = β = 90, γ = 120° and contain two molecules of molecular weight 13500 per asymmetric unit. The crystals diffract up to a resolution of 2.2 Å and are suitable for X-ray diffraction analysis.