Crystal structure of the cytokinin-producing enzyme "lonely guy" (LOG) from Mycobacterium tuberculosis

Mycobacterium tuberculosis (Mtb) is an extremely successful intracellular pathogen that cause a large number of death worldwide. It is interesting that this non-phytopathogen can synthesize cytokinin by "lonely guy" (LOG) protein. The cytokinin biosynthesis pathway in Mtb is not clear. Here we determined the crystal structure of LOG from Mtb (MtLOG) at a high resolution of 1.8 Å. MtLOG exists as dimer which belongs to type-I LOG and shows a typical α-β Rossmann fold. Like other LOGs, MtLOG also contains a conserved "PGGXGTXXE" motif that contributes to the formation of an active site. For the first time, we found that the MtLOG binds to Mg²⁺ in the negative potential pocket. According to the docking result, we found that Arg78, Arg98 and Tyr162 should be the key amino acid involved in substrate binding. Our findings provide a structural basis for cytokinin study in Mtb and will play an important role in design and development of enzyme inhibitors.