Examining cooperative gating phenomena in voltage-dependent potassium channels: taking the energetic approach

Allosteric regulation of protein function is often achieved by changes in protein conformation induced by changes in chemical or electrical potential. In multisubunit proteins, such conformational changes may give rise to cooperativity in ligand binding. Conformational changes between open and closed states are central to the function of voltage-activated potassium (Kv) channel proteins, homotetrameric pore-forming membrane proteins involved in generating and shaping action potentials in excitable cells. Accessible to extremely high signal-to-noise ratio in functional measurements, combined with the availability of high-resolution structural data for different conformations of the protein, the Kv channel represents an excellent allosteric model system to further understand the aspects of synergism and cooperative effects in protein function. In this chapter, we demonstrate how the use of the simple law of mass action combined with thermodynamic mutant cycle energetic coupling analysis of Kv channel gating can be used to provide valuable information regarding (1) how cooperativity in Kv channel pore opening can be assessed; (2) how one can directly discriminate whether conformational transitions during Kv channel pore opening occur in a concerted or sequential manner; and (3) how mechanistically, the coupling between distant activation gate and selectivity filter functional elements of the prototypical Shaker Kv channel protein might be achieved. In addition to providing valuable insight into the function of this important protein, the conclusions reached at using high-order thermodynamic energetic coupling analysis applied to the Kv channel allosteric model system reveal much about the function of allosteric proteins, in general.