Effect of a bound anion on the structure and dynamics of halorhodopsin from .

Active ion transport across membranes is vital to maintaining the electrochemical gradients of ions in cells and is mediated by transmembrane proteins. Halorhodopsin (HR) functions as a light-driven inward pump for chloride ions. The protein contains all--retinal bound to a specific lysine residue through a protonated Schiff base.