The protein MabA of Mycobacterium tuberculosis is a beta-ketoacyl reductase (KAR) and catalyses one of the four steps of the fatty acid elongation system FAS-II. The crystal structures of different KARs revealed a significant rearrangements of the active site between a "closed" inactive conformation and an "open" and active form in presence of the cofactor. MabA is a potential therapeutic target. However, only the structure of the "closed" form was obtained and rational drug design requires the structure of the active form. Here we described the sequences and structures analysis of the KARs to stabilize the "open form" in MabA. The crystal structure of a mutated MabA protein was then solved in both inactive and active form. The crystal structure of the wild-type MabA in the presence of NADP was also solved and showing a mixture of the two mutually exclusive conformations. This new structure of MabA is analyzed in view of its distinctive enzymatic and structural properties and those of related enzymes.
(c) 2005 Wiley-Liss, Inc.