Expression, purification, crystallization and preliminary X-ray diffraction analysis of Sagittaria sagittifolia arrowhead protease inhibitor API-A in complex with bovine trypsin.

Protease inhibitors play key roles in physiological processes. Arrowhead protease inhibitor A (API-A), a member of the serine protease inhibitor family, can inhibit two trypsin molecules simultaneously. In the present work, API-A from Sagittaria sagittifolia has been cloned, expressed, purified and crystallized in complex with bovine trypsin. The crystals were obtained by the sitting-drop method. A data set was collected to 2.48 A resolution from a single crystal. The crystal belonged to space group C222(1), with unit-cell parameters a = 76.63, b = 110.86, c = 152.99 A, alpha = beta = gamma = 90 degrees .