Macromolecular structure and interaction studies of SigF and Usfx in Mycobacterium tuberculosis.

Mycobacterium tuberculosis (Mtb) is an intracellular human parasite that causes tuberculosis (TB). The parasite is capable of surviving under stress conditions. The gene expression in Mtb is regulated by sigma factor family of proteins. The SigF protein belongs to the sigma factor family, expressed during stationary and growth phase, 14 genes are directly regulated by SigF and has a role in the expression of the principal sigma factor SigB as well. The interacting partner Usfx, the anti SigF protein, controls the regulation of SigF. The structures of SigF and Usfx were evaluated using comparative modelling techniques and validated. The active sites of the two proteins were identified. The protein-protein interaction studies between SigF and Usfx reveal His53, Phe226 and Asp227 residues of SigF protein to be involved in binding with Arg108, Arg130 and Glu140 amino acids of Usfx. The present study focuses on identification of important residues involved in binding of SigF protein with Usfx, which are essential in the inhibition of transcription initiation and survival of Mtb.