Na(+) Binding and Transport: Insights from Light-Driven Na(+)-Pumping Rhodopsin

Na(+) plays a vital role in numerous physiological processes across humans and animals, necessitating a comprehensive understanding of Na(+) transmembrane transport. Among the various Na(+) pumps and channels, light-driven Na(+)-pumping rhodopsin (NaR) has emerged as a noteworthy model in this field. This review offers a concise overview of the structural and functional studies conducted on NaR, encompassing ground/intermediate-state structures and photocycle kinetics. The primary focus lies in addressing key inquiries: (1) unraveling the translocation pathway of Na(+); (2) examining the role of structural changes within the photocycle, particularly in the O state, in facilitating Na(+) transport; and (3) investigating the timing of Na(+) uptake/release. By delving into these unresolved issues and existing debates, this review aims to shed light on the future direction of Na(+) pump research.