Modeling the stimulation by glutathione of the steady state kinetics of an adenosine triphosphate binding cassette transporter

We report the steady state ATPase activities of the ATP Binding Cassette (ABC) exporter NaAtm1 in the absence and presence of a transported substrate, oxidized glutathione (GSSG), in detergent, nanodiscs, and proteoliposomes. The steady state kinetic data were fit to the nonessential activator model where the basal ATPase rate of the transporter is stimulated by GSSG. The detailed kinetic parameters varied between the different reconstitution conditions, highlighting the importance of the lipid environment for NaAtm1 function. The increased ATPase rates in the presence of GSSG more than compensate for the modest negative cooperativity observed between MgATP and GSSG in lipid environments. These studies highlight the central role of the elusive ternary complex in accelerating the ATPase rate that is at the heart of coupling mechanism between substrate transport and ATP hydrolysis.

Automated summary

The ATPase activities of the ABC transporter NaAtm1 were investigated in different lipid environments, showing that oxidized glutathione can stimulate the ATPase rate. The detailed kinetic parameters varied between different reconstitution conditions, indicating the importance of the lipid environment for NaAtm1 function. The elusive ternary complex plays a central role in accelerating the ATPase rate, which is crucial for the coupling mechanism between substrate transport and ATP hydrolysis.