Characterization of α-isopropylmalate synthases containing different copy numbers of tandem repeats in Mycobacterium tuberculosis

Background  

Alpha-isopropylmalate synthase (α-IPMS) is the key enzyme that catalyzes the first committed step in the leucine biosynthetic pathway. The gene encoding α-IPMS in Mycobacterium tuberculosis, leuA, is polymorphic due to the insertion of 57-bp repeat units referred to as Variable Number of Tandem Repeats (VNTR). The role of the VNTR found within the M. tuberculosis genome is unclear. To investigate the role of the VNTR in leuA, we compared two α-IPMS proteins with different numbers of amino acid repeats, one with two copies and the other with 14 copies. We have cloned leuA with 14 copies of the repeat units into the pET15b expression vector with a His₆-tag at the N-terminus, as was previously done for the leuA gene with two copies of the repeat units.