CO2 directly modulates connexin 26 by formation of carbamate bridges between subunits

Abstract

Homeostatic regulation of the partial pressure of CO2 (PCO2) is vital for life. Sensing of pH has been proposed as a sufficient proxy for determination of PCO2 and direct CO2-sensing largely discounted. Here we show that connexin 26 (C×26) hemichannels, causally linked to respiratory chemosensitivity, are directly modulated by CO2. A 'carbamylation motif', present in CO2-sensitive connexins (C×26, C×30, C×32) but absent from a CO2-insensitive connexin (C×31), comprises Lys125 and four further amino acids that orient Lys125 towards Arg104 of the adjacent subunit of the connexin hexamer. Introducing the carbamylation motif into C×31 created a mutant hemichannel (mC×31) that was opened by increases in PCO2. Mutation of the carbamylation motif in C×26 and mC×31 destroyed CO2 sensitivity. Course-grained computational modelling of C×26 demonstrated that the proposed carbamate bridge between Lys125 and Arg104 biases the hemichannel to the open state. Carbamylation of C×26 introduces a new transduction principle for physiological sensing of CO2. © Meigh et al.