Purification and crystallization of human cathepsin D

The two-chain form of human cathepsin D was purified from human spleen with a method utilizing an ion exchange chromatography step prior to the pepstatin affinity column normally used to purify aspartic proteases. The protein was crystallized from 21% polyethylene glycol 8000 at pH 4.0 using the hanging drop vapour diffusion method. Small crystals were used as seeds to grow crystals suitable for X-ray data collection. The crystals diffract to a resolution of 3.2 Å and have space group P2 1 2 1 2 1 with unit cell dimensions a = 59.9 A ̊ , b = 99.6 A ̊ , c = 133.6 A ̊ . There are two molecules in the asymmetric unit.