A novel 40 kDa protein from goat mammary secretions: purification, crystallization and preliminary X-ray diffraction studies

A novel 40 kDa protein has been purified from dry secretions of the mammary gland of goats. The first 15 N-terminal residues were sequenced and showed a sequence identity of 30% to a novel 39 kDa whey protein from bovine mamm ary secretions. The protein was crystallized by the microdialysis method. P rotein was dissolved to a concentration of 40 mg ml(-1) in 0.025 M Tris-HCl pH 8.0 and equilibrated with the same buffer containing 19%(v/v) ethanol. The crystals belong to the orthorhombic space group P2(1)2(1)2(1), with uni t-cell parameters a = 66.1, b = 107.8, c = 63.2 Angstrom and one molecule p er asymmetric unit. Intensity data were collected to 2.9 Angstrom resolutio n, with a completeness of 95%. Since no similar model is available in the p rotein structure database, heavy-atom derivatives have been prepared and th ree-dimensional structure determination using the isomorphous replacement m ethod is in progress.