Energy profiles in the acetylcholine receptor (AChR) channel. The MII-helix model and the role of the remaining helices.

It is demonstrated by theoretical computations that no favorable energy profile for cation transfer can be obtained in a model of the AChR channel constructed with the sole five MII helices of the inner wall. A favorable profile is obtained upon including the effect of the remaining helices of the five subunits. The decisive role, for the exit of the ion, of the charged residues situated at the N-terminal of the MII segments, established before, is underlined further. The role of the other elements of the channel wall (peptide carbonyl oxygens, hydrocarbon residues and polar side chains) is analyzed.