A Steric “Ball-and-Chain” Mechanism for pH-Mediated Regulation of Gap Junction Channels

Khan, Ali K.; Jagielnicki, Maciej; McIntire, William E.; Purdy, Michael D.; Dharmarajan, Venkatasubramanian; Griffin, Patrick R.; Yeager, Mark

doi:10.1016/j.celrep.2020.03.046

Cited by 45 publications

(57 citation statements)

References 84 publications

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“…Such changes will only cause modest intracellular acidification. By contrast very profound acidification to pH values below 6.5 is required to close the Cx26 gap junction channel (Khan et al, 2020). Secondly, and more importantly, the mutation K125R prevents the CO2-dependent closure of the gap junction, but does not affect the closing effect of acidification induced by application of propionate (Figure 4).…”

Section: Independence Of Ph-and Co2-dependent Modulation Of Cx26 Gap mentioning

confidence: 99%

Opposing modulation of Cx26 gap junctions and hemichannels by CO₂

Nijjar

Maddison

Meigh

et al. 2019

Preprint

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Cx26 hemichannels are opened by modest levels of CO2 (PCO2 55 mmHg) acting via a novel carbamylation mechanism to bias the hemichannel to the open state. In the hemichannel, CO2 nonenzymatically carbamylates Lys125, and the resulting carbamate forms a salt bridge to Arg104 of the neighbouring subunit. By contrast, similar modest levels of CO2 cause Cx26 gap junction closure.Gap junctions of Cx31, a beta connexin that lacks the carbamylation motif, are insensitive to these levels of CO2. Mutations of the carbamylation motif, Lys125Arg and Arg104Ala, which abrogate hemichannel opening in Cx26, also prevent gap junction closing. Elastic network modelling suggests that the lowest entropy state, when CO2 is bound, is in the open configuration for the hemichannel and the closed configuration for the gap junction Surprisingly, we conclude that the opposing actions of CO2 on Cx26 gap junctions and hemichannels results from carbamylation of the same residues.

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Section: Independence Of Ph-and Co2-dependent Modulation Of Cx26 Gap mentioning

confidence: 99%

Opposing modulation of Cx26 gap junctions and hemichannels by CO₂

Nijjar

Maddison

Meigh

et al. 2019

Preprint

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“…Previous studies have suggested that channel gating may involve marked conformational changes of NTHs in connexin protomers (17,18). Charged residues in NTHs have been believed to form at least part of transjunctional voltage sensor (19,20).…”

Section: Introductionmentioning

confidence: 99%

Cryo-EM structure of human Cx31.3/GJC3 connexin hemichannel

et al. 2020

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Connexin family proteins assemble into hexameric channels called hemichannels/connexons, which function as transmembrane channels or dock together to form gap junction intercellular channels (GJIChs). We determined the cryo–electron microscopy structures of human connexin 31.3 (Cx31.3)/GJC3 hemichannels in the presence and absence of calcium ions and with a hearing-loss mutation R15G at 2.3-, 2.5-, and 2.6-Å resolutions, respectively. Compared with available structures of GJICh in open conformation, Cx31.3 hemichannel shows substantial structural changes of highly conserved regions in the connexin family, including opening of calcium ion–binding tunnels, reorganization of salt-bridge networks, exposure of lipid-binding sites, and collocation of amino-terminal helices at the cytoplasmic entrance. We also found that the hemichannel has a pore with a diameter of ~8 Å and selectively transports chloride ions. Our study provides structural insights into the permeant selectivity of Cx31.3 hemichannel.

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“…The gating action of CO 2 on Cx26 is therefore mediated via movements of the N-terminal helix and its ability to plug the channel. This same mechanism (movement of the N-terminal helix) has been proposed to gate the channel in response to signals such as voltage or pH 20 . Presumably, the structural drivers and critical residues for initiating movement of the N-terminal helix are different for these three modifiers of Cx26 gating.…”

Section: Discussionmentioning

confidence: 75%

“…The resolution is much higher than has been seen for previous structures of Cx26 20,33,34 , enabling the protein to be modelled more accurately. Relative to these structures, the most interesting differences involve the N-terminus.…”

Section: Introductionmentioning

confidence: 94%

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Conformational changes and channel gating induced by CO₂binding to Connexin26

et al. 2020

Preprint

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CO2 is the inevitable by-product of oxidative metabolism. Many physiological processes such as breathing1 and cerebral blood flow2 are sensitive to CO2. Historically, the physiological actions of CO2 have been regarded as being mediated exclusively via changes in pH. Here, we change this consensus by showing that the gap junction protein Connexin26 (Cx26) acts as a receptor for CO2 showing sensitivity to modest changes in PCO2 around the physiological norm3-6. Mass spectrometry analysis7 shows that CO2 carbamylates 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 PCO2 of 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 CO2 involves movements of the N-terminus to plug the channel at high PCO2. We therefore provide mechanistic detail for a new paradigm by which CO2 can directly control breathing8 and other key physiological functions9.

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A Steric “Ball-and-Chain” Mechanism for pH-Mediated Regulation of Gap Junction Channels

Cited by 45 publications

References 84 publications

Opposing modulation of Cx26 gap junctions and hemichannels by CO₂

Opposing modulation of Cx26 gap junctions and hemichannels by CO₂

Cryo-EM structure of human Cx31.3/GJC3 connexin hemichannel

Conformational changes and channel gating induced by CO₂binding to Connexin26

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A Steric “Ball-and-Chain” Mechanism for pH-Mediated Regulation of Gap Junction Channels

Cited by 45 publications

References 84 publications

Opposing modulation of Cx26 gap junctions and hemichannels by CO2

Opposing modulation of Cx26 gap junctions and hemichannels by CO2

Cryo-EM structure of human Cx31.3/GJC3 connexin hemichannel

Conformational changes and channel gating induced by CO2binding to Connexin26

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Opposing modulation of Cx26 gap junctions and hemichannels by CO₂

Opposing modulation of Cx26 gap junctions and hemichannels by CO₂

Conformational changes and channel gating induced by CO₂binding to Connexin26