Octahedral Trifluoromagnesate, an Anomalous Metal Fluoride Species, Stabilizes the Transition State in a Biological Motor.

Isoelectronic metal fluoride transition state analogue (TSA) complexes, MgF and AlF , have proven to be immensely useful in understanding mechanisms of biological motors utilizing phosphoryl transfer. Here we report a previously unobserved octahedral TSA complex, MgF(HO), in a 1.5 Å resolution Zika virus NS3 helicase crystal structure. F NMR provided independent validation and also the direct observation of conformational tightening resulting from ssRNA binding in solution. The TSA stabilizes the two conformations of motif V of the helicase that link ATP hydrolysis with mechanical work. DFT analysis further validated the MgF(HO) species, indicating the significance of this TSA for studies of biological motors.