Mycobacterium tuberculosis proteins and protein compositions that are components of a desaturase complex are provided. The Mycobacterium tuberculosis desaturase complex may include a desaturase and an oxidoreductase. The complex may include the rv3229c and rv3230c gene products of Mycobacterium tuberculosis. Vectors for expressing the desaturase and the oxidoreductase can be packaged together, including a label that indicates their use as a complex for analyzing desaturation of fatty acids. In addition, methods for screening target ligands specific for a desaturase complex are also provided.