obtained and 6 structures were determined. Among them, Bs139 protein functions as phosphoribosylglycinamide formyltransferase (GART), an important enzyme in the de novo pathway of purine biosynthesis. Bs139 crystal diffracted to 2.5 Å resolution at home Xray source and the structure was determined by molecular replacement (MR). Bs154 protein is a putative deoxyuridine 5'-triphosphate nucleotidehydrolase (dUTPase), which plays important role in DNA replication. Se-YosS crystal diffraction datasets were collected at Beijing Synchrotron Radiation Facility (BSRF) and the structure was determined by multi-wavelength anomalous diffraction (MAD) method.

Rv2844 is a conserved hypothetical protein from M. tuberculosis. Among the 4.5 million protein sequences in the non-redundant (NR) sequence database, only 12 proteins share sequence homology with Rv2844, and none of them has a known function. The crystal structure of Rv2844 was determined by Se-SAD experiments and refined at 2.0Å resolution. It revealed a fold of a 4-helix bundle closely related to the Ferritin-like iron storage and electron transport proteins. It is quite possible that Rv2844 defines a novel class of 4-helix bundle metal-binding proteins. High-throughput ligand analysis (Roberts and Kim, to be published) suggested that Rv2844 strongly interacts with s-adenosylmethionine (SAM), a coenzyme involved in more than 40 metabolic reactions in cells. Structural study of Rv2844-SAM complex is underway to understand the nature of their interaction. Since Rv2844 has no sequence homologs in higher organisms, and since experimental data strongly indicate Rv2844's relationship to proteins critical to cell's metabolic pathways, we are in the process of evaluating Rv2844's potential as a drug target. Updated results will be presented.