HUMAN LIVER CATHEPSIN-D - PURIFICATION, CRYSTALLIZATION AND PRELIMINARY-X-RAY DIFFRACTION ANALYSIS OF A LYSOSOMAL-ENZYME

The two-chain form of active cathepsin D, a glycosylated, lysosomal aspartic proteinase, has been isolated from human liver. Isoelectric focusing revealed two major species of enzyme that differed by approximately 0·2 pI unit. Crystals suitable for X-ray diffraction analysis were prepared from acidic solutions using precipitation with ammonium sulfate. The hexagonal crystals diffracted X-rays to beyond 3·1 Å resolution and belonged to space group P61 (or P65) with cell constants a = b = 125·9 A ̊, c = 104·1 A ̊, γ = 120·0 °. The crystals likely contain two molecules in the asymmetric unit, giving a solvent content of 56% ( v w). Biochemical analysis of crystals indicated that both isoforms were present in approximately equimolar proportions. Full structure determination of the enzyme is underway. © 1992.