Changing Val-76 towards Kir channels drastically influences the folding and gating properties of the bacterial potassium channel KcsA

Inferring functional units in ion channel pores via relative entropy

Coarse-grained protein models approximate the first-principle physical potentials. Among those modeling approaches, the relative entropy framework yields promising and physically sound results, in which a mapping from the target protein structure and dynamics to a model is defined and subsequently adjusted by an entropy minimization of the model parameters. Minimization of the relative entropy is equivalent to maximization of the likelihood of reproduction of (configurational ensemble) observations by the model. In this study, we extend the relative entropy minimization procedure beyond parameter fitting by a second optimization level, which identifies the optimal mapping to a (dimension-reduced) topology. We consider anisotropic network models of a diverse set of ion channels and assess our findings by comparison to experimental results.

Mutations in the K(+)-channel KcsA toward Kir channels alter salt-induced clusterization and blockade by quaternary alkylammonium ions

Protein aggregation is a result of malfunction in protein folding, assembly, and transport, caused by protein mutation and/or changes in the cell environment, thus triggering many human diseases. We have shown that bacterial K(+)-channel KcsA, which acts as a representative model for ion channels, forms salt-induced large conductive complexes in a particular environment. In the present study, we investigated the effects of point mutations in the selectivity filter of KcsA on intrinsic stability, aggregation, and channel blocking behavior. First, we found that a low sodium chloride concentration in potassium-containing media induced fast transfer of single channels to a planar lipid bilayer. Second, increasing the sodium chloride concentration drastically increased the total channel current, indicating enhanced vesicle fusion and transfer of multiple channels to a planar lipid bilayer. However, such complexes exhibited high conductance as well as higher open probability compared to the unmodified KcsA behavior shown previously. Interestingly, the affinity of aggregated complexes for larger symmetric quaternary alkylammonium ions (QAs) was found to be much higher than that for tetraethylammonium, a classical blocker of the K(+) channel. Based on these findings, we propose that mutant channel complexes exhibit larger pore dimensions, thus resembling more the topological properties of voltage-gated and inwardly rectifying K(+) channels.