Crystallization and preliminary X-ray crystallographic analysis of the 38-kDa immunodominant antigen of Mycobacterium tuberculosis.

The 38-kDa lipoprotein is one of the most potent cell surface immunogens of Mycobacterium tuberculosis in antibody-and T cell-mediated reactions. Using a pure recombinant form of the protein, we have recently shown that it binds phosphate much like that of the phosphate-binding protein (M(r) = 34.4 kDa) that is localized in the periplasm of Escherichia coli and is involved as an initial receptor for active transport of phosphate. The purified 38-kDa protein has been crystallized in 2 forms that are suitable for high-resolution structural analyses. One form belongs to the monoclinic space group P2(1) with unit cell dimensions of a = 67.42 A, b = 113.38 A, c = 42.68 A, and beta = 108.53 degrees. The other is of orthorhombic space group P2(1)2(1)2 with a = 125.46 A, b = 72.27 A, and c = 73.43 A. Both crystal forms diffract to about 2 A resolution on a fine focus rotating anode.