Conformational changes and channel gating induced by CO2binding to Connexin26

Abstract

AbstractCO2is the inevitable by-product of oxidative metabolism. Many physiological processes such as breathing1and cerebral blood flow2are sensitive to CO2. Historically, the physiological actions of CO2have been regarded as being mediated exclusivelyviachanges in pH. Here, we change this consensus by showing that the gap junction protein Connexin26 (Cx26) acts as a receptor for CO2showing sensitivity to modest changes in PCO2around the physiological norm3-6. Mass spectrometry analysis7shows that CO2carbamylates specific lysines on a regulatory loop of Cx26 at high, but not at low levels of PCO2. By means of high resolution cryo-EM, we have solved structures of Cx26 gap junctions at 1.9, 2.2 and 2.1 Å for PCO2of 90, 55 and 20 mmHg respectively, all at pH 7.4. Classification of the particles at each level of PCO2, shows the transmembrane helices and N-terminal helix flexing at the dynamic cytoplasmic side of the protein. Gating of Cx26 gap junctions by CO2involves movements of the N-terminus to plug the channel at high PCO2. We therefore provide mechanistic detail for a new paradigm by which CO2can directly control breathing8and other key physiological functions9.