Preliminary structural studies on the leucine-zipper homology region of the human protein Bap31.

B-cell receptor-associated protein 31 (Bap31) is an integral membrane protein located in the endoplasmic reticulum (ER) that participates in the transport and quality control of membrane proteins and plays a role in determining cell sensitivity to ER stress and apoptosis. Its cytoplasmic region contains two target sites for caspase cleavage in certain apoptotic pathways. Here, the subcloning, expression, purification and crystallization of the Homo sapiens Bap31 leucine-zipper C-terminal fragment, which spans residues Gly160-Glu246, are reported. An N-terminally His-tagged protein was overexpressed in Escherichia coli and purified by chromatographic methods. X-ray diffraction data were collected in-house to 2.5 A resolution. Crystals belong to space group P6(1)22/P6(5)22, with unit-cell parameters a = b = 70.7, c = 80.6 A. Data analysis indicates the presence of one molecule per asymmetric unit.