Cyclic nucleotide-gated channels: Shedding light on the opening of a channel pore

Few proteins have been described functionally in such detail as ion channel s. All ion channels open and close their ion-conducting pores, a process re ferred to as gating. The recent crystallization of the P-loop-containing ch annel KcsA has cast channel function in a new light. Results relating to a variety of P-loop-containing channels are converging on a common mechanism in which separation of the inner helices that line the pore results in chan nel opening. At the same time, differences-some subtle and some perhaps mor e profound-have emerged between channel types. Here we highlight the eviden ce for a specific conformational change during the gating of cyclic nucleot ide-gated channels, and compare and contrast this evidence to that obtained for other channels.