ABSTRACT
The structures shown above opened up a field that will most likely expand in many directions. Next, the structures of the intracellular domains of the two-segment K+ channels (e.g., KcsA or Kir channels with extensive intracellular N and C termini) may be expected, as well as the structure of the six-segment K+ or Na+ channels, including the mechanism of voltage-driven gating or the receptors for the respective IDs. Such data will verify whether the KcsA structure is indeed the minimal pore of all types of K+ channels, whether the structural changes associated with pH gating in KcsA is meaningful for voltage-driven activation, or how the ID-receptor complex of a Kv channel may look. Moreover, some recently discovered gating mechanisms based on the interaction of channel a subunits with further proteins (such as interaction of a six-segment K+ channel with calmodulin that reconstituted a K+ channel gated by submicromolar calcium, or gating of Kir channels by G proteins) await structural investigations. It is hoped that close correlation of such structural work with func tional characterization will somehow provide a complete understanding of the channel work and its role in physiological systems.
