Crystallization of chicken egg white cystatin, a low molecular weight protein inhibitor of cysteine proteinases, and preliminary X-ray diffraction data.

The shorter-chain form of chicken egg white cystatin has been crystallized in 1.6 M-phosphate buffer at pH 4.0 by vapour diffusion. The crystals are of trigonal space group P3121 (or P3221), have cell constants a = b = 47.9 A, c = 87.5 A, alpha = beta = 90 degrees, gamma = 120 degrees, and contain one molecule of 12,191 molecular weight per asymmetric unit. They diffract well to about 2.0 A resolution and are suitable for X-ray crystal structure analysis.