The catalytic activity and binding of mutant S220T in M. tuberculosis IGP Synthase

Tuberculosis (TB) is a serious infectious disease that mainly affects the lungs, and if not treated properly it can be fatal. It is caused by a bacterium called Mycobacterium tuberculosis, which is developing drug resistance with time. The goal is to create a new drug that will battle Mycobacterium tuberculosis. The enzyme IGPS was adopted as a drug target because of its role in the tryptophan biosynthetic pathways. The enzyme Indole -3-glycerol phosphate synthase (MtIGPS) catalyzes one step in the tryptophan biosynthetic pathway. It converts the substrate CDRP to the product IGP. In this lab,the residue S220 was mutated to a threonine (T). The S220T mutant was then studied to compare its catalytic activity and substrate binding to the wildtype. A Michaelis - Menten experiment was performed to study the catalytic activity and substrate binding of the enzyme S220T in M. tuberculosis IGPS. The Km value of wild type is 6.07 uM and the Km for the S220T mutant is 41.1 uM.The kcat calculated for S220T was 1.19x10-3 s-1. S220 residue is important in catalysis because the activity decreased around 49.4 times compared to the wild type and also in binding because the new km is so much higher than the old Km. These data suggest that S220 plays a role in substrate binding and this interaction should be considered when designing potential drug molecules.