Fig. 5.

A working model of how HmpF regulates the T4P in response to light. Light absorbed by the photosystems (PSI + PSII) drives linear and cyclic electron flow, resulting in proton pumping via the cytochrome complex (cyt). The efflux of protons from the cytoplasm into the thylakoid space could result in a change to the membrane potential (ΔmV) across the cytoplasmic membrane and might serve as a signal sensed by HmpD, which in turn stimulates the Hmp system to regulate HmpF interaction with components at the base of the T4P. OM: outermembrane; PP: periplasm; CM: cytoplasmic membrane; TM: thylakoid membrane; ETC: respiratory electron transport chain.