A Chloride Pump at Atomic Resolution

In Halobacterium salinarum , a family of four archaeal rhodopsins performs several different signaling and cross-membrane transport functions. In this Perspective, Spudich discusses recent advances in understanding the molecular mechanism by which these homologous proteins perform this range of functions. A high-resolution structure of halorhodopsin (Kolbe et al. , page 1390) provides insights into the relation between proton and chloride transport, representing an important step toward understanding the unifying principles in the archaeal rhodopsin family.