Visualizing the stochastic gating of Na+/H+ antiporters in single native bacteria

Abstract

Na+/H+ antiporters are the major secondary transporters that regulate pH and sodium homeostasis by enabling transmembrane exchanges of Na+ with H+ in opposite directions, both are essential cations. Although their crystal structures and functions have been well characterized1-3, the transport dynamics of Na+/H+ antiporters during action in living cells remained largely unexplored. Herein, intermittent blinking of the spontaneous bioluminescence from single native bioluminescent bacteria, P. phosphoreum, was reported, investigated and attributed to the stochastic gating of Na+/H+ antiporters between the active and inactive conformations. Each gating event caused the rapid depolarization and recovery of membrane potential within several seconds, accompanying with the intermittent bioluminescence blinking due to the transient inhibitions on the activity of respiratory chain. Temperature-dependent measurements further revealed that the conformational change was thermodynamically driven with an activation energy barrier of 20.3 kJ/mol. While the stochastic gating of ion channels has been well understood for decades4,5, this study uncovered the stochastic gating dynamics of Na+/H+ antiporters, another major pathway for ion transmembrane transports, in single native bacteria without any genetic engineering or chemical labeling. It also opened the door for P. phosphoreum to serve as new model bacteria for reporting the physiological and metabolic status with spontaneous bioluminescence emission.