The Mycothiol -transferase is Divalent Metal-dependent for Mycothiol Binding and Transfer

Mycothiol -transferase (MST) (encoded by the gene) was previously identified as the enzyme responsible for the transfer of Mycothiol (MSH) to xenobiotic acceptors in () during xenobiotic stress. To further characterize the functionality of MST and the possible roles , X-ray crystallographic, metal-dependent enzyme kinetics, thermal denaturation studies, and antibiotic MIC determination in knockout strain were performed. The binding of MSH and Zn increases the melting temperature by 12.9 °C as a consequence of the cooperative stabilization of MST by both MSH and metal. The co-crystal structure of MST in complex with MSH and Zn to 1.45 Å resolution supports the specific utilization of MSH as a substrate as well as affording insights into the structural requirements of MSH binding and the metal-assisted catalytic mechanism of MST. Contrary to the well-defined role of MSH in mycobacterial xenobiotic responses and the ability of MST to bind MSH, cell-based studies with an knockout strain failed to provide evidence for a role of MST in processing of rifampicin or isoniazid. These studies suggest the necessity of a new direction to identify acceptors of the enzyme and better define the biological role of MST in mycobacteria.