A comparative biochemical and structural analysis of the intracellular chorismate mutase (Rv0948c) from Mycobacterium tuberculosis H 37 R v and the secreted chorismate mutase (y2828) from Yersinia pestis

The Rv0948c gene from Mycobacterium tuberculosis H 37 R v encodes a 90 amino acid protein as the natural gene product with chorismate mutase (CM) activity. The protein, 90‐MtCM, exhibits Michaelis–Menten kinetics with a k cat of 5.5 ± 0.2 s −1 and a K m of 1500 ± 100 μ m at 37 °C and pH 7.5. The 2.0 Å X‐ray structure shows that 90‐MtCM is an all α‐helical homodimer (Protein Data Bank ID: 2QBV) with the topology of Escherichia coli CM (EcCM), and that both protomers contribute to each catalytic site. Superimposition onto the structure of EcCM and the sequence alignment shows that the C‐terminus helix 3 is shortened. The absence of two residues in the active site of 90‐MtCM corresponding to Ser84 and Gln88 of EcCM appears to be one reason for the low k cat . Hence, 90‐MtCM belongs to a subfamily of α‐helical AroQ CMs termed AroQ δ. The CM gene (y2828) from Yersinia pestis encodes a 186 amino acid protein with an N‐terminal signal peptide that directs the protein to the periplasm. The mature protein, *YpCM, exhibits Michaelis–Menten kinetics with a k cat of 70 ± 5 s −1 and K m of 500 ± 50 μ m at 37 °C and pH 7.5. The 2.1 Å X‐ray structure shows that *YpCM is an all α‐helical protein, and functions as a homodimer, and that each protomer has an independent catalytic unit (Protein Data Bank ID: 2GBB). *YpCM belongs to the AroQ γ class of CMs, and is similar to the secreted CM (Rv1885c, *MtCM) from M. tuberculosis .