Protons at the Kv1.2 channel gate can close the gate.

Abstract

Quantum calculations have shown that the voltage sensing domain (VSD) can produce protons when the membrane is polarized (Kariev and Green, JPCB (2019) 123,7984); more recently, two paths for the protons to reach the gate along the intracellular surface of the membrane have been calculated (idem, Membranes (2022) 12,718). We now present evidence that the protons at the gate can prevent potassium transmission, that is, they close the gate. Roughly 6 Å intracellular to the well-known PVPV ring, there is a triad of amino acids (using 3Lut (PDB) numbering: S411, N412, N414) that sits just beyond the end of the transmission paths, which end with H418 and E327; the calculations show how it is responsible for receiving the protons, in a somewhat surprising manner. We have calculated several cases, with one or two protons in each domain in different positions at this triad, and with chloride counterions. This comes close to the PVPV ring. With one proton per domain, with or without a Cl- included in the calculation, the potential is not sufficient to block an incoming K+ ion. With two H+ and one Cl- per domain, it appears that there is a substantial barrier to the entrance of a K+ ion; one H neutralizes E327, the other forms a hydronium—Cl- pair that interacts with K+, stopping it. The protons can therefore close the gate, without calling for any major conformational changes. Quantitative results for energy as a function of K+ ion position with the protons in place (closed) and not in place (open) will be presented. These calculations show how the arrangement of the water is critical as the protons reach their positions at the gate.