Biochemical and biophysical characterization of nucleotide binding domain of Trehalose transporter from Mycobacterium...

The SugABC is an ABC transporter in Mycobacterium tuberculosis which is proposed to be involved in the process of Trehalose import, but till date the proteins of this transporter complex have not been functionally characterized. This transport process is driven by the nucleotide binding domain SugC of SugABC transporter. To understand the functional role of SugC, we expressed and purified the protein in E.coli. Our purification result shows, Mtb SugC exists as a monomer in solution but forms dimers upon binding to ATP. It is stable at pH 7.5 as analyzed by CD spectroscopy and showed maximum activity at this pH as estimated by Michaelis-Menten's kinetics for Mg-ATP at a K_M of 0.15 mM. The SugC^H193A mutant was observed to have a reduced catalytic activity implying that H193 is one of the residues involved in the hydrolysis of ATP. The molecular modeling further revealed that, like E.coli MalK, MtbSugC also has an ATPase domain and a regulatory domain. Despite having low sequence homology with other nucleotide binding domains of ABC transporters, the structure and functional motifs of MtbSugC are conserved. Thus, we show that SugC is a functional ATPase domain of SugABC transporter in Mycobacterium tuberculosis.