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Gaete PS, Kumar D, Fernandez CI, Valdez Capuccino JM, Bhatt A, Jiang W, Lin YC, Liu Y, Harris AL, Luo YL, Contreras JE. Large-pore connexin hemichannels function like molecule transporters independent of ion conduction. Proc Natl Acad Sci U S A 2024; 121:e2403903121. [PMID: 39116127 PMCID: PMC11331127 DOI: 10.1073/pnas.2403903121] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2024] [Accepted: 07/05/2024] [Indexed: 08/10/2024] Open
Abstract
Connexin hemichannels were identified as the first members of the eukaryotic large-pore channel family that mediate permeation of both atomic ions and small molecules between the intracellular and extracellular environments. The conventional view is that their pore is a large passive conduit through which both ions and molecules diffuse in a similar manner. In stark contrast to this notion, we demonstrate that the permeation of ions and of molecules in connexin hemichannels can be uncoupled and differentially regulated. We find that human connexin mutations that produce pathologies and were previously thought to be loss-of-function mutations due to the lack of ionic currents are still capable of mediating the passive transport of molecules with kinetics close to those of wild-type channels. This molecular transport displays saturability in the micromolar range, selectivity, and competitive inhibition, properties that are tuned by specific interactions between the permeating molecules and the N-terminal domain that lies within the pore-a general feature of large-pore channels. We propose that connexin hemichannels and, likely, other large-pore channels, are hybrid channel/transporter-like proteins that might switch between these two modes to promote selective ion conduction or autocrine/paracrine molecular signaling in health and disease processes.
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Affiliation(s)
- Pablo S. Gaete
- Department of Physiology and Membrane Biology, School of Medicine, University of California, Davis, CA95616
| | - Deepak Kumar
- Department of Biotechnology and Pharmaceutical Sciences, College of Pharmacy, Western University of Health Sciences, Pomona, CA91766
| | - Cynthia I. Fernandez
- Department of Physiology and Membrane Biology, School of Medicine, University of California, Davis, CA95616
| | - Juan M. Valdez Capuccino
- Department of Pharmacology, Physiology, and Neuroscience, New Jersey Medical School, Rutgers, The State University of New Jersey, Newark, NJ07103
| | - Aashish Bhatt
- Department of Biotechnology and Pharmaceutical Sciences, College of Pharmacy, Western University of Health Sciences, Pomona, CA91766
| | - Wenjuan Jiang
- Department of Biotechnology and Pharmaceutical Sciences, College of Pharmacy, Western University of Health Sciences, Pomona, CA91766
| | - Yi-Chun Lin
- Department of Biotechnology and Pharmaceutical Sciences, College of Pharmacy, Western University of Health Sciences, Pomona, CA91766
| | - Yu Liu
- Department of Pharmacology, Physiology, and Neuroscience, New Jersey Medical School, Rutgers, The State University of New Jersey, Newark, NJ07103
| | - Andrew L. Harris
- Department of Pharmacology, Physiology, and Neuroscience, New Jersey Medical School, Rutgers, The State University of New Jersey, Newark, NJ07103
| | - Yun L. Luo
- Department of Biotechnology and Pharmaceutical Sciences, College of Pharmacy, Western University of Health Sciences, Pomona, CA91766
| | - Jorge E. Contreras
- Department of Physiology and Membrane Biology, School of Medicine, University of California, Davis, CA95616
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2
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Su Y, Verkhratsky A, Yi C. Targeting connexins: possible game changer in managing neuropathic pain? Trends Mol Med 2024; 30:642-659. [PMID: 38594094 DOI: 10.1016/j.molmed.2024.03.009] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2024] [Revised: 03/08/2024] [Accepted: 03/18/2024] [Indexed: 04/11/2024]
Abstract
Neuropathic pain is a chronic debilitating condition caused by nerve injury or a variety of diseases. At the core of neuropathic pain lies the aberrant neuronal excitability in the peripheral and/or central nervous system (PNS and CNS). Enhanced connexin expression and abnormal activation of connexin-assembled gap junctional channels are prominent in neuropathic pain along with reactive gliosis, contributing to neuronal hypersensitivity and hyperexcitability. In this review, we delve into the current understanding of how connexin expression and function contribute to the pathogenesis and pathophysiology of neuropathic pain and argue for connexins as potential therapeutic targets for neuropathic pain management.
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Affiliation(s)
- Yixun Su
- Research Centre, Seventh Affiliated Hospital of Sun Yat-sen University, Shenzhen, China
| | - Alexei Verkhratsky
- Faculty of Biology, Medicine and Health, The University of Manchester, Manchester, UK; Achucarro Center for Neuroscience, IKERBASQUE, Bilbao, Spain; Department of Stem Cell Biology, State Research Institute Centre for Innovative Medicine, Vilnius, Lithuania; Department of Forensic Analytical Toxicology, School of Forensic Medicine, China Medical University, Shenyang, China.
| | - Chenju Yi
- Research Centre, Seventh Affiliated Hospital of Sun Yat-sen University, Shenzhen, China; Guangdong Provincial Key Laboratory of Brain Function and Disease, Guangzhou, China; Shenzhen Key Laboratory of Chinese Medicine Active substance screening and Translational Research, Shenzhen, China.
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3
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Brotherton DH, Nijjar S, Savva CG, Dale N, Cameron AD. Structures of wild-type and a constitutively closed mutant of connexin26 shed light on channel regulation by CO 2. eLife 2024; 13:RP93686. [PMID: 38829031 PMCID: PMC11147507 DOI: 10.7554/elife.93686] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/05/2024] Open
Abstract
Connexins allow intercellular communication by forming gap junction channels (GJCs) between juxtaposed cells. Connexin26 (Cx26) can be regulated directly by CO2. This is proposed to be mediated through carbamylation of K125. We show that mutating K125 to glutamate, mimicking the negative charge of carbamylation, causes Cx26 GJCs to be constitutively closed. Through cryo-EM we observe that the K125E mutation pushes a conformational equilibrium towards the channel having a constricted pore entrance, similar to effects seen on raising the partial pressure of CO2. In previous structures of connexins, the cytoplasmic loop, important in regulation and where K125 is located, is disordered. Through further cryo-EM studies we trap distinct states of Cx26 and observe density for the cytoplasmic loop. The interplay between the position of this loop, the conformations of the transmembrane helices and the position of the N-terminal helix, which controls the aperture to the pore, provides a mechanism for regulation.
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Affiliation(s)
| | - Sarbjit Nijjar
- School of Life Sciences, University of WarwickCoventryUnited Kingdom
| | - Christos G Savva
- Leicester Institute of Structural and Chemical Biology, Department of Molecular and Cell Biology, University of LeicesterLeicesterUnited Kingdom
| | - Nicholas Dale
- School of Life Sciences, University of WarwickCoventryUnited Kingdom
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4
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Patil ND, Bains A, Kaur S, Yadav R, Goksen G, Ali N, AlAsmari AF, Chawla P. Effect of dual modifications with ultrasonication and succinylation on Cicer arietinum protein-iron complexes: Characterization, digestibility, in-vitro cellular mineral uptake and preparation of fortified smoothie. Food Res Int 2024; 186:114344. [PMID: 38729696 DOI: 10.1016/j.foodres.2024.114344] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2023] [Revised: 04/07/2024] [Accepted: 04/17/2024] [Indexed: 05/12/2024]
Abstract
The research aimed to evaluate the effect of ultrasonication and succinylation on the functional, iron binding, physiochemical, and cellular mineral uptake efficacy of chickpea protein concentrate. Succinylation resulted in significant improvements in the water-holding capacity (WHC) (25.47 %), oil-holding capacity (OHC) (31.38 %), and solubility (5.80 %) of the chickpea protein-iron complex. Mineral bioavailability significantly increased by 4.41 %, and there was a significant increase in cellular mineral uptake (64.64 %), retention (36.68 %), and transport (27.96 %). The ferritin content of the succinylated chickpea protein-iron complex showed a substantial increase of 66.31%. Furthermore, the dual modification approach combining ultrasonication and succinylation reduced the particle size of the protein-iron complex with a substantial reduction of 83.25 %. It also resulted in a significant enhancement of 51.5 % in the SH (sulfhydryl) content and 48.92 % in the surface hydrophobicity. Mineral bioavailability and cellular mineral uptake, retention, and transport were further enhanced through dual modification. In terms of application, the addition of single and dual-modified chickpea protein-iron complex to a fruit-based smoothie demonstrated positive acceptance in sensory attributes. Overall, the combined approach of succinylation and ultrasonication to the chickpea protein-iron complex shows a promising strategy for enhancing the physiochemical and techno-functional characteristics, cellular mineral uptake, and the development of vegan food products.
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Affiliation(s)
- Nikhil Dnyaneshwar Patil
- Department of Food Technology and Nutrition, Lovely Professional University, Phagwara, Punjab 144411, India
| | - Aarti Bains
- Department of Microbiology, Lovely Professional University, Phagwara 144411, Punjab, India
| | - Sawinder Kaur
- Department of Food Technology and Nutrition, Lovely Professional University, Phagwara, Punjab 144411, India
| | - Rahul Yadav
- Shoolini Life Sciences Pvt. Ltd., Shoolini University, Solan 173229, Himachal Pradesh, India
| | - Gulden Goksen
- Department of Food Technology, Vocational School of Technical Sciences at Mersin Tarsus Organized Industrial Zone, Tarsus University, 33100 Mersin, Turkey.
| | - Nemat Ali
- Département of Pharmacology and Toxicology, Collège of Pharmacy, King Saud University, P.O. Box 2457, Riyadh 11451, Saudi Arabia
| | - Abdullah F AlAsmari
- Département of Pharmacology and Toxicology, Collège of Pharmacy, King Saud University, P.O. Box 2457, Riyadh 11451, Saudi Arabia
| | - Prince Chawla
- Department of Food Technology and Nutrition, Lovely Professional University, Phagwara, Punjab 144411, India.
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5
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Mickus R, Raškevičius V, Sarapinienė I, Mikalayeva V, Prekeris R, Skeberdis VA. Phosphorylation-dependent allosteric regulation of Cx43 gap junction inhibitor potency. Biomed Pharmacother 2024; 174:116550. [PMID: 38593702 DOI: 10.1016/j.biopha.2024.116550] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2024] [Revised: 03/28/2024] [Accepted: 04/04/2024] [Indexed: 04/11/2024] Open
Abstract
Physiological and pathological processes such as homeostasis, embryogenesis, development, tumorigenesis, and cell movement depend on the intercellular communication through gap junctions (GJIC). Connexin (Cx)-based GJ channels are formed of two apposing hemichannels in the contiguous cells and provide a direct pathway for electrical and metabolic intercellular communication. The main modulators of GJ conductance are transjunctional voltage, intracellular pH, Ca2+, Mg2+, and phosphorylation. Chemical modulators of GJIC are being used in cases of various intercellular communication-dependent diseases. In this study, we used molecular docking, dual whole-cell patch-clamp, and Western blotting to investigate the impact of connexin phosphorylation on GJ chemical gating by α-pinene and other GJ inhibitors (octanol, carbenoxolone, mefloquine, intracellular pH, glycyrrhetinic acid, and sevoflurane) in HeLa cells expressing exogenous Cx43 (full length and truncated at amino acid 258) and other connexins typical of heart and/or nervous system (Cx36, Cx40, Cx45, and Cx47), and in cells expressing endogenous Cx43 (Novikoff and U-87). We found that Ca2+-regulated kinases, such as Ca2+/calmodulin-dependent kinase II, atypical protein kinase C, cyclin-dependent kinase, and Pyk2 kinase may allosterically modulate the potency of α-pinene through phosphorylation of Cx43 C-terminus. The identified new phenomenon was Cx isoform-, inhibitor-, and cell type-dependent. Overall, these results suggest that compounds, the potency of which depends on receptor phosphorylation, might be of particular interest in developing targeted therapies for diseases accompanied by high kinase activity, such as cardiac arrhythmias, epilepsy, stroke, essential tremor, inflammation, and cancer.
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Affiliation(s)
- Rokas Mickus
- Institute of Cardiology, Lithuanian University of Health Sciences, Kaunas LT-50162, Lithuania
| | - Vytautas Raškevičius
- Institute of Cardiology, Lithuanian University of Health Sciences, Kaunas LT-50162, Lithuania
| | - Ieva Sarapinienė
- Institute of Cardiology, Lithuanian University of Health Sciences, Kaunas LT-50162, Lithuania
| | - Valeryia Mikalayeva
- Institute of Cardiology, Lithuanian University of Health Sciences, Kaunas LT-50162, Lithuania
| | - Rytis Prekeris
- Department of Cell and Developmental Biology, University of Colorado Anschutz Medical Campus, Aurora, CO 80015, USA
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6
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Jagielnicki M, Kucharska I, Bennett BC, Harris AL, Yeager M. Connexin Gap Junction Channels and Hemichannels: Insights from High-Resolution Structures. BIOLOGY 2024; 13:298. [PMID: 38785780 PMCID: PMC11117596 DOI: 10.3390/biology13050298] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/26/2024] [Revised: 03/29/2024] [Accepted: 04/08/2024] [Indexed: 05/25/2024]
Abstract
Connexins (Cxs) are a family of integral membrane proteins, which function as both hexameric hemichannels (HCs) and dodecameric gap junction channels (GJCs), behaving as conduits for the electrical and molecular communication between cells and between cells and the extracellular environment, respectively. Their proper functioning is crucial for many processes, including development, physiology, and response to disease and trauma. Abnormal GJC and HC communication can lead to numerous pathological states including inflammation, skin diseases, deafness, nervous system disorders, and cardiac arrhythmias. Over the last 15 years, high-resolution X-ray and electron cryomicroscopy (cryoEM) structures for seven Cx isoforms have revealed conservation in the four-helix transmembrane (TM) bundle of each subunit; an αβ fold in the disulfide-bonded extracellular loops and inter-subunit hydrogen bonding across the extracellular gap that mediates end-to-end docking to form a tight seal between hexamers in the GJC. Tissue injury is associated with cellular Ca2+ overload. Surprisingly, the binding of 12 Ca2+ ions in the Cx26 GJC results in a novel electrostatic gating mechanism that blocks cation permeation. In contrast, acidic pH during tissue injury elicits association of the N-terminal (NT) domains that sterically blocks the pore in a "ball-and-chain" fashion. The NT domains under physiologic conditions display multiple conformational states, stabilized by protein-protein and protein-lipid interactions, which may relate to gating mechanisms. The cryoEM maps also revealed putative lipid densities within the pore, intercalated among transmembrane α-helices and between protomers, the functions of which are unknown. For the future, time-resolved cryoEM of isolated Cx channels as well as cryotomography of GJCs and HCs in cells and tissues will yield a deeper insight into the mechanisms for channel regulation. The cytoplasmic loop (CL) and C-terminal (CT) domains are divergent in sequence and length, are likely involved in channel regulation, but are not visualized in the high-resolution X-ray and cryoEM maps presumably due to conformational flexibility. We expect that the integrated use of synergistic physicochemical, spectroscopic, biophysical, and computational methods will reveal conformational dynamics relevant to functional states. We anticipate that such a wealth of results under different pathologic conditions will accelerate drug discovery related to Cx channel modulation.
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Affiliation(s)
- Maciej Jagielnicki
- The Phillip and Patricia Frost Institute for Chemistry and Molecular Science, Department of Chemistry, University of Miami, 1201 Memorial Drive, Miami, FL 33146, USA; (M.J.); (I.K.)
| | - Iga Kucharska
- The Phillip and Patricia Frost Institute for Chemistry and Molecular Science, Department of Chemistry, University of Miami, 1201 Memorial Drive, Miami, FL 33146, USA; (M.J.); (I.K.)
| | - Brad C. Bennett
- Department of Biological and Environmental Sciences, Howard College of Arts and Sciences, Samford University, Birmingham, AL 35229, USA;
| | - Andrew L. Harris
- Rutgers New Jersey Medical School, Department of Pharmacology, Physiology and Neuroscience, Newark, NJ 07103, USA;
| | - Mark Yeager
- The Phillip and Patricia Frost Institute for Chemistry and Molecular Science, Department of Chemistry, University of Miami, 1201 Memorial Drive, Miami, FL 33146, USA; (M.J.); (I.K.)
- The Phillip and Patricia Frost Institute for Chemistry and Molecular Science, Department of Biochemistry and Molecular Biology, University of Miami, Miami, FL 33146, USA
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7
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Fu YH, Hu YF, Lin T, Zhuang GW, Wang YL, Chen WX, Li ZT, Hou JL. Constructing artificial gap junctions to mediate intercellular signal and mass transport. Nat Chem 2024:10.1038/s41557-024-01519-8. [PMID: 38658798 DOI: 10.1038/s41557-024-01519-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2023] [Accepted: 03/25/2024] [Indexed: 04/26/2024]
Abstract
Natural gap junctions are a type of channel protein responsible for intercellular signalling and mass communication. However, the scope of applications for these proteins is limited as they cannot be prepared at a large scale and are unable to spontaneously insert into cell membranes in vitro. The construction of artificial gap junctions may provide an alternative strategy for preparing analogues of the natural proteins and bottom-up building blocks necessary for the synthesis of artificial cells. Here we show the construction of artificial gap junction channels from unimolecular tubular molecules consisting of alternately arranged positively and negatively charged pillar[5]arene motifs. These molecules feature a hydrophobic-hydrophilic-hydrophobic triblock structure that allows them to efficiently insert into two adjacent plasma membranes and stretch across the gap between the two membranes to form gap junctions. Similar to natural gap junction channels, the synthetic channels could mediate intercellular signal coupling and reactive oxygen species transmission, leading to cellular activity.
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Affiliation(s)
- Yong-Hong Fu
- Department of Chemistry, Fudan University, Shanghai, China
| | - Yi-Fei Hu
- Department of Chemistry, Fudan University, Shanghai, China
| | - Tao Lin
- Department of Chemistry, Fudan University, Shanghai, China
| | - Guo-Wei Zhuang
- Department of Chemistry, Fudan University, Shanghai, China
| | - Ying-Lan Wang
- Department of Chemistry, Fudan University, Shanghai, China
| | - Wen-Xue Chen
- Department of Chemistry, Fudan University, Shanghai, China
| | - Zhan-Ting Li
- Department of Chemistry, Fudan University, Shanghai, China
| | - Jun-Li Hou
- Department of Chemistry, Fudan University, Shanghai, China.
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8
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Mao W, Chen S. Assembly mechanisms of the neuronal gap junction channel connexin 36 elucidated by Cryo-EM. Arch Biochem Biophys 2024; 754:109959. [PMID: 38490311 DOI: 10.1016/j.abb.2024.109959] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2023] [Revised: 01/20/2024] [Accepted: 03/12/2024] [Indexed: 03/17/2024]
Abstract
Electrical synapses are essential components of neural circuits. Neuronal signal transduction across electrical synapses is primarily mediated by gap junction channels composed of Connexin36 (Cx36), the lack of which causes impaired electrical coupling between certain neurons including cortical interneurons and thalamic reticular nucleus (TRN) neurons. However, the structural basis underlying Cx36 function and assembly remains elusive. Recently, Lee et al. reported cryo-EM structures of Cx36, thus provided first insights of its gating mechanism. Here, we report a consistent cryo-EM structure of Cx36 determined in parallel, and describe unique interactions underpinning its assembly mechanism in complementary to the competing work. In particular, we found non-canonical electrostatic interactions between protomers from opposing hemichannels and a steric complementary site between adjacent protomers within a hemichannel, which together provide a structural explanation for the assembly specificity in homomeric and heteromeric gap junction channels.
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Affiliation(s)
- Wenxuan Mao
- Department of Otolaryngology-Head and Neck Surgery, Shanghai Ninth People's Hospital, Shanghai, China; Ear Institute, Shanghai Jiao Tong University School of Medicine, Shanghai, China; Shanghai Key Laboratory of Translational Medicine on Ear and Nose Diseases, Shanghai, China; Shanghai Institute of Precision Medicine, Ninth People's Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, China
| | - Shanshuang Chen
- Department of Otolaryngology-Head and Neck Surgery, Shanghai Ninth People's Hospital, Shanghai, China; Ear Institute, Shanghai Jiao Tong University School of Medicine, Shanghai, China; Shanghai Key Laboratory of Translational Medicine on Ear and Nose Diseases, Shanghai, China; Shanghai Institute of Precision Medicine, Ninth People's Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, China.
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9
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Héja L, Simon Á, Kardos J. Simulation of gap junction formation reveals critical role of Cys disulfide redox state in connexin hemichannel docking. Cell Commun Signal 2024; 22:185. [PMID: 38500186 PMCID: PMC10949817 DOI: 10.1186/s12964-023-01439-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2023] [Accepted: 12/12/2023] [Indexed: 03/20/2024] Open
Abstract
Video Abstract.
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Affiliation(s)
- László Héja
- Institute of Organic Chemistry, Research Centre for Natural Sciences, Magyar Tudósok Körútja 2, 1117, Budapest, Hungary.
| | - Ágnes Simon
- Institute of Organic Chemistry, Research Centre for Natural Sciences, Magyar Tudósok Körútja 2, 1117, Budapest, Hungary
| | - Julianna Kardos
- Institute of Organic Chemistry, Research Centre for Natural Sciences, Magyar Tudósok Körútja 2, 1117, Budapest, Hungary
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10
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Wong RS, Chen H, Li YX, Esseltine JL, Stathopulos PB, Bai D. Human Cx50 Isoleucine177 prevents heterotypic docking and formation of functional gap junction channels with Cx43. Am J Physiol Cell Physiol 2024; 326:C414-C428. [PMID: 38145302 DOI: 10.1152/ajpcell.00634.2023] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2023] [Revised: 12/18/2023] [Accepted: 12/18/2023] [Indexed: 12/26/2023]
Abstract
The human lens is an avascular organ, and its transparency is dependent on gap junction (GJ)-mediated microcirculation. Lens GJs are composed of three connexins with Cx46 and Cx50 being expressed in lens fiber cells and Cx43 and Cx50 in the epithelial cells. Impairment of GJ communication by either Cx46 or Cx50 mutations has been shown to be one of the main molecular mechanisms of congenital cataracts in mutant carrier families. The docking compatibility and formation of functional heterotypic GJs for human lens connexins have not been studied. Previous study on rodent lens connexins revealed that Cx46 can form functional heterotypic GJs with Cx50 and Cx43, but Cx50 cannot form heterotypic GJ with Cx43 due to its second extracellular (EL2) domain. To study human lens connexin docking and formation of functional heterotypic GJs, we developed a genetically engineered HEK293 cell line with endogenously expressed Cx43 and Cx45 ablated. The human lens connexins showed docking compatibility identical to those found in the rodent connexins. To reveal the structural mechanisms of the docking incompatibility between Cx50 and Cx43, we designed eight variants based on the differences between the EL2 of Cx50 and Cx46. We found that Cx50I177L is sufficient to establish heterotypic docking with Cx43 with some interesting gating properties. Our structure models indicate this residue is important for interdomain interactions within a single connexin, Cx50 I177L showed an increased interdomain interaction which might alter the docking interface structure to be compatible with Cx43.NEW & NOTEWORTHY The human lens is an avascular organ, and its transparency is partially dependent on gap junction (GJ) network composed of Cx46, Cx50, and Cx43. We found that human Cx46 can dock and form functional heterotypic GJs with Cx50 and Cx43, but Cx50 is unable to form functional heterotypic GJs with Cx43. Through mutagenesis and patch-clamp study of several designed variants, we found that Cx50 I177L was sufficient to form functional heterotypic GJs with Cx43.
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Affiliation(s)
- Robert S Wong
- Department of Physiology and Pharmacology, University of Western Ontario, London, Ontario, Canada
| | - Honghong Chen
- Department of Physiology and Pharmacology, University of Western Ontario, London, Ontario, Canada
| | - Yi X Li
- Department of Physiology and Pharmacology, University of Western Ontario, London, Ontario, Canada
| | - Jessica L Esseltine
- Division of BioMedical Sciences, Faculty of Medicine, Memorial University of Newfoundland, St. John's, Newfoundland and Labrador, Canada
| | - Peter B Stathopulos
- Department of Physiology and Pharmacology, University of Western Ontario, London, Ontario, Canada
| | - Donglin Bai
- Department of Physiology and Pharmacology, University of Western Ontario, London, Ontario, Canada
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11
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Lucaciu SA, Leighton SE, Hauser A, Yee R, Laird DW. Diversity in connexin biology. J Biol Chem 2023; 299:105263. [PMID: 37734551 PMCID: PMC10598745 DOI: 10.1016/j.jbc.2023.105263] [Citation(s) in RCA: 8] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2023] [Revised: 09/08/2023] [Accepted: 09/14/2023] [Indexed: 09/23/2023] Open
Abstract
Over 35 years ago the cell biology community was introduced to connexins as the subunit employed to assemble semicrystalline clusters of intercellular channels that had been well described morphologically as gap junctions. The decade that followed would see knowledge of the unexpectedly large 21-member human connexin family grow to reflect unique and overlapping expression patterns in all organ systems. While connexin biology initially focused on their role in constructing highly regulated intercellular channels, this was destined to change as discoveries revealed that connexin hemichannels at the cell surface had novel roles in many cell types, especially when considering connexin pathologies. Acceptance of connexins as having bifunctional channel properties was initially met with some resistance, which has given way in recent years to the premise that connexins have multifunctional properties. Depending on the connexin isoform and cell of origin, connexins have wide-ranging half-lives that vary from a couple of hours to the life expectancy of the cell. Diversity in connexin channel characteristics and molecular properties were further revealed by X-ray crystallography and single-particle cryo-EM. New avenues have seen connexins or connexin fragments playing roles in cell adhesion, tunneling nanotubes, extracellular vesicles, mitochondrial membranes, transcription regulation, and in other emerging cellular functions. These discoveries were largely linked to Cx43, which is prominent in most human organs. Here, we will review the evolution of knowledge on connexin expression in human adults and more recent evidence linking connexins to a highly diverse array of cellular functions.
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Affiliation(s)
- Sergiu A Lucaciu
- Department of Anatomy and Cell Biology, University of Western Ontario, London, Ontario, Canada; Department of Physiology and Pharmacology, University of Western Ontario, London, Ontario, Canada
| | - Stephanie E Leighton
- Department of Anatomy and Cell Biology, University of Western Ontario, London, Ontario, Canada
| | - Alexandra Hauser
- Department of Anatomy and Cell Biology, University of Western Ontario, London, Ontario, Canada
| | - Ryan Yee
- Department of Physiology and Pharmacology, University of Western Ontario, London, Ontario, Canada
| | - Dale W Laird
- Department of Anatomy and Cell Biology, University of Western Ontario, London, Ontario, Canada; Department of Physiology and Pharmacology, University of Western Ontario, London, Ontario, Canada.
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12
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Qi C, Lavriha P, Bayraktar E, Vaithia A, Schuster D, Pannella M, Sala V, Picotti P, Bortolozzi M, Korkhov VM. Structures of wild-type and selected CMT1X mutant connexin 32 gap junction channels and hemichannels. SCIENCE ADVANCES 2023; 9:eadh4890. [PMID: 37647412 PMCID: PMC10468125 DOI: 10.1126/sciadv.adh4890] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/07/2023] [Accepted: 07/27/2023] [Indexed: 09/01/2023]
Abstract
In myelinating Schwann cells, connection between myelin layers is mediated by gap junction channels (GJCs) formed by docked connexin 32 (Cx32) hemichannels (HCs). Mutations in Cx32 cause the X-linked Charcot-Marie-Tooth disease (CMT1X), a degenerative neuropathy without a cure. A molecular link between Cx32 dysfunction and CMT1X pathogenesis is still missing. Here, we describe the high-resolution cryo-electron cryo-myography (cryo-EM) structures of the Cx32 GJC and HC, along with two CMT1X-linked mutants, W3S and R22G. While the structures of wild-type and mutant GJCs are virtually identical, the HCs show a major difference: In the W3S and R22G mutant HCs, the amino-terminal gating helix partially occludes the pore, consistent with a diminished HC activity. Our results suggest that HC dysfunction may be involved in the pathogenesis of CMT1X.
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Affiliation(s)
- Chao Qi
- Institute of Molecular Biology and Biophysics, ETH Zurich, Zurich, Switzerland
- Laboratory of Biomolecular Research, Paul Scherrer Institute, Villigen, Switzerland
| | - Pia Lavriha
- Institute of Molecular Biology and Biophysics, ETH Zurich, Zurich, Switzerland
- Laboratory of Biomolecular Research, Paul Scherrer Institute, Villigen, Switzerland
| | - Erva Bayraktar
- Veneto Institute of Molecular Medicine (VIMM), Padua, Italy
- Department of Physics and Astronomy “G. Galilei”, University of Padua, Padua, Italy
| | - Anand Vaithia
- Institute of Molecular Biology and Biophysics, ETH Zurich, Zurich, Switzerland
- Laboratory of Biomolecular Research, Paul Scherrer Institute, Villigen, Switzerland
| | - Dina Schuster
- Institute of Molecular Biology and Biophysics, ETH Zurich, Zurich, Switzerland
- Laboratory of Biomolecular Research, Paul Scherrer Institute, Villigen, Switzerland
- Institute of Molecular Systems Biology, ETH Zurich, Zurich, Switzerland
| | - Micaela Pannella
- Veneto Institute of Molecular Medicine (VIMM), Padua, Italy
- Department of Physics and Astronomy “G. Galilei”, University of Padua, Padua, Italy
| | - Valentina Sala
- Veneto Institute of Molecular Medicine (VIMM), Padua, Italy
| | - Paola Picotti
- Institute of Molecular Systems Biology, ETH Zurich, Zurich, Switzerland
| | - Mario Bortolozzi
- Veneto Institute of Molecular Medicine (VIMM), Padua, Italy
- Department of Physics and Astronomy “G. Galilei”, University of Padua, Padua, Italy
| | - Volodymyr M. Korkhov
- Institute of Molecular Biology and Biophysics, ETH Zurich, Zurich, Switzerland
- Laboratory of Biomolecular Research, Paul Scherrer Institute, Villigen, Switzerland
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13
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Matusevičiūtė R, Ignatavičiūtė E, Mickus R, Bordel S, Skeberdis VA, Raškevičius V. Evaluation of Cx43 Gap Junction Inhibitors Using a Quantitative Structure-Activity Relationship Model. Biomedicines 2023; 11:1972. [PMID: 37509611 PMCID: PMC10377234 DOI: 10.3390/biomedicines11071972] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2023] [Revised: 07/07/2023] [Accepted: 07/10/2023] [Indexed: 07/30/2023] Open
Abstract
Gap junctions (GJs) made of connexin-43 (Cx43) are necessary for the conduction of electrical impulses in the heart. Modulation of Cx43 GJ activity may be beneficial in the treatment of cardiac arrhythmias and other dysfunctions. The search for novel GJ-modulating agents using molecular docking allows for the accurate prediction of binding affinities of ligands, which, unfortunately, often poorly correlate with their potencies. The objective of this study was to demonstrate that a Quantitative Structure-Activity Relationship (QSAR) model could be used for more precise identification of potent Cx43 GJ inhibitors. Using molecular docking, QSAR, and 3D-QSAR, we evaluated 16 known Cx43 GJ inhibitors, suggested the monocyclic monoterpene d-limonene as a putative Cx43 inhibitor, and tested it experimentally in HeLa cells expressing exogenous Cx43. The predicted concentrations required to produce 50% of the maximal effect (IC50) for each of these compounds were compared with those determined experimentally (pIC50 and eIC50, respectively). The pIC50ies of d-limonene and other Cx43 GJ inhibitors examined by our QSAR and 3D-QSAR models showed a good correlation with their eIC50ies (R = 0.88 and 0.90, respectively) in contrast to pIC50ies obtained from molecular docking (R = 0.78). However, molecular docking suggests that inhibitor potency may depend on their docking conformation on Cx43. Searching for new potent, selective, and specific inhibitors of GJ channels, we propose to perform the primary screening of new putative compounds using the QSAR model, followed by the validation of the most suitable candidates by patch-clamp techniques.
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Affiliation(s)
- Ramona Matusevičiūtė
- Faculty of Medicine, Lithuanian University of Health Sciences, 03101 Kaunas, Lithuania; (R.M.); (E.I.)
| | - Eglė Ignatavičiūtė
- Faculty of Medicine, Lithuanian University of Health Sciences, 03101 Kaunas, Lithuania; (R.M.); (E.I.)
| | - Rokas Mickus
- Institute of Cardiology, Lithuanian University of Health Sciences, 50162 Kaunas, Lithuania; (R.M.); (S.B.); (V.A.S.)
| | - Sergio Bordel
- Institute of Cardiology, Lithuanian University of Health Sciences, 50162 Kaunas, Lithuania; (R.M.); (S.B.); (V.A.S.)
- Institute of Sustainable Processes, University of Valladolid, 47011 Valladolid, Spain
| | - Vytenis Arvydas Skeberdis
- Institute of Cardiology, Lithuanian University of Health Sciences, 50162 Kaunas, Lithuania; (R.M.); (S.B.); (V.A.S.)
| | - Vytautas Raškevičius
- Institute of Cardiology, Lithuanian University of Health Sciences, 50162 Kaunas, Lithuania; (R.M.); (S.B.); (V.A.S.)
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14
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Lee SN, Cho HJ, Jeong H, Ryu B, Lee HJ, Kim M, Yoo J, Woo JS, Lee HH. Cryo-EM structures of human Cx36/GJD2 neuronal gap junction channel. Nat Commun 2023; 14:1347. [PMID: 36906653 PMCID: PMC10008584 DOI: 10.1038/s41467-023-37040-8] [Citation(s) in RCA: 6] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2022] [Accepted: 02/28/2023] [Indexed: 03/13/2023] Open
Abstract
Connexin 36 (Cx36) is responsible for signal transmission in electrical synapses by forming interneuronal gap junctions. Despite the critical role of Cx36 in normal brain function, the molecular architecture of the Cx36 gap junction channel (GJC) is unknown. Here, we determine cryo-electron microscopy structures of Cx36 GJC at 2.2-3.6 Å resolutions, revealing a dynamic equilibrium between its closed and open states. In the closed state, channel pores are obstructed by lipids, while N-terminal helices (NTHs) are excluded from the pore. In the open state with pore-lining NTHs, the pore is more acidic than those in Cx26 and Cx46/50 GJCs, explaining its strong cation selectivity. The conformational change during channel opening also includes the α-to-π-helix transition of the first transmembrane helix, which weakens the protomer-protomer interaction. Our structural analyses provide high resolution information on the conformational flexibility of Cx36 GJC and suggest a potential role of lipids in the channel gating.
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Affiliation(s)
- Seu-Na Lee
- Department of Life Sciences, Korea University, Seoul, 02841, Republic of Korea
| | - Hwa-Jin Cho
- Department of Chemistry, College of Natural Sciences, Seoul National University, Seoul, 08826, Korea
| | - Hyeongseop Jeong
- Center for Research Equipment, Korea Basic Science Institute, Chungcheongbuk-do, 28119, Korea
| | - Bumhan Ryu
- Research Solution Center, Institute for Basic Science, Daejeon, 34126, Republic of Korea
| | - Hyuk-Joon Lee
- Department of Life Sciences, Korea University, Seoul, 02841, Republic of Korea
| | - Minsoo Kim
- Department of Physics, Sungkyunkwan University, Suwon, 16419, South Korea
| | - Jejoong Yoo
- Department of Physics, Sungkyunkwan University, Suwon, 16419, South Korea
| | - Jae-Sung Woo
- Department of Life Sciences, Korea University, Seoul, 02841, Republic of Korea.
| | - Hyung Ho Lee
- Department of Chemistry, College of Natural Sciences, Seoul National University, Seoul, 08826, Korea.
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