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 (Mr = 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 P21 with unit cell dimensions of a = 67.42 Å, b = 113.38 Å, c = 42.68 Å, and β = 108.53°. The other is of the orthorhombic space group P21212 with a = 125.46 Å, b = 72.27 Å, and c = 73.43 Å. Both crystal forms diffract to about 2 Å resolution on a fine focus rotating anode.