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Li H, Spagnol G, Pontifex TK, Burt JM, Sorgen PL. Chemical shift assignments of the connexin37 carboxyl terminal domain. BIOMOLECULAR NMR ASSIGNMENTS 2017; 11:137-141. [PMID: 28251507 PMCID: PMC5581280 DOI: 10.1007/s12104-017-9735-x] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/25/2016] [Accepted: 02/20/2017] [Indexed: 05/07/2023]
Abstract
Connexin37 (Cx37) is a gap junction protein involved in cell-to-cell communication in the vasculature and other tissues. Cx37 suppresses proliferation of vascular cells involved in tissue development and repair in vivo, as well as tumor cells. Global deletion of Cx37 in mice leads to enhanced vasculogenesis in development, as well as collateralgenesis and angiogenesis in response to injury, which together support improved tissue remodeling and recovery following ischemic injury. Here we report the 1H, 15N, and 13C resonance assignments for an important regulatory domain of Cx37, the carboxyl terminus (CT; C233-V333). The predicted secondary structure of the Cx37CT domain based on the chemical shifts is that of an intrinsically disordered protein. In the 1H-15N HSQC, N-terminal residues S254-Y259 displayed a second weaker peak and residues E261-Y266 had significant line broadening. These residues are flanked by prolines (P250, P258, P260, and P268), suggesting proline cis-trans isomerization. Overall, these assignments will be useful for identifying the binding sites for intra- and inter-molecular interactions that affect Cx37 channel activity.
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Affiliation(s)
- Hanjun Li
- Department of Biochemistry and Molecular Biology, University of Nebraska Medical Center, Omaha, NE, 68198, USA
| | - Gaelle Spagnol
- Department of Biochemistry and Molecular Biology, University of Nebraska Medical Center, Omaha, NE, 68198, USA
| | - Tasha K Pontifex
- Department of Physiology, University of Arizona, Tucson, AZ, USA
| | - Janis M Burt
- Department of Physiology, University of Arizona, Tucson, AZ, USA
| | - Paul L Sorgen
- Department of Biochemistry and Molecular Biology, University of Nebraska Medical Center, Omaha, NE, 68198, USA.
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Spagnol G, Al-Mugotir M, Kopanic JL, Zach S, Li H, Trease AJ, Stauch KL, Grosely R, Cervantes M, Sorgen PL. Secondary structural analysis of the carboxyl-terminal domain from different connexin isoforms. Biopolymers 2016; 105:143-62. [PMID: 26542351 DOI: 10.1002/bip.22762] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2015] [Revised: 10/27/2015] [Accepted: 10/28/2015] [Indexed: 12/19/2022]
Abstract
The connexin carboxyl-terminal (CxCT) domain plays a role in the trafficking, localization, and turnover of gap junction channels, as well as the level of gap junction intercellular communication via numerous post-translational modifications and protein-protein interactions. As a key player in the regulation of gap junctions, the CT presents itself as a target for manipulation intended to modify function. Specific to intrinsically disordered proteins, identifying residues whose secondary structure can be manipulated will be critical toward unlocking the therapeutic potential of the CxCT domain. To accomplish this goal, we used biophysical methods to characterize CxCT domains attached to their fourth transmembrane domain (TM4). Circular dichroism and nuclear magnetic resonance were complementary in demonstrating the connexin isoforms that form the greatest amount of α-helical structure in their CT domain (Cx45 > Cx43 > Cx32 > Cx50 > Cx37 ≈ Cx40 ≈ Cx26). Studies compared the influence of 2,2,2-trifluoroethanol, pH, phosphorylation, and mutations (Cx32, X-linked Charcot-Marie Tooth disease; Cx26, hearing loss) on the TM4-CxCT structure. While pH modestly influences the CT structure, a major structural change was associated with phosphomimetic substitutions. Since most connexin CT domains are phosphorylated throughout their life cycle, studies of phospho-TM4-CxCT isoforms will be critical toward understanding the role that structure plays in regulating gap junction function.
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Affiliation(s)
- Gaëlle Spagnol
- Department of Biochemistry and Molecular Biology, University of Nebraska Medical Center, Omaha, NE, 68198
| | - Mona Al-Mugotir
- Department of Biochemistry and Molecular Biology, University of Nebraska Medical Center, Omaha, NE, 68198
| | - Jennifer L Kopanic
- Department of Biochemistry and Molecular Biology, University of Nebraska Medical Center, Omaha, NE, 68198
| | - Sydney Zach
- Department of Biochemistry and Molecular Biology, University of Nebraska Medical Center, Omaha, NE, 68198
| | - Hanjun Li
- Department of Biochemistry and Molecular Biology, University of Nebraska Medical Center, Omaha, NE, 68198
| | - Andrew J Trease
- Department of Biochemistry and Molecular Biology, University of Nebraska Medical Center, Omaha, NE, 68198
| | - Kelly L Stauch
- Department of Biochemistry and Molecular Biology, University of Nebraska Medical Center, Omaha, NE, 68198
| | - Rosslyn Grosely
- Department of Biochemistry and Molecular Biology, University of Nebraska Medical Center, Omaha, NE, 68198
| | - Matthew Cervantes
- Department of Biochemistry and Molecular Biology, University of Nebraska Medical Center, Omaha, NE, 68198
| | - Paul L Sorgen
- Department of Biochemistry and Molecular Biology, University of Nebraska Medical Center, Omaha, NE, 68198
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Degradation of gap junction connexins is regulated by the interaction with Cx43-interacting protein of 75 kDa (CIP75). Biochem J 2015; 466:571-85. [PMID: 25583071 DOI: 10.1042/bj20141042] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
Connexins are a family of transmembrane proteins that form gap junction channels. These proteins undergo both proteasomal and lysosomal degradation, mechanisms that serve to regulate connexin levels. Our previous work described CIP75 [connexin43 (Cx43)-interacting protein of 75 kDa], a protein involved in proteasomal degradation, as a novel Cx43-interacting protein. We have discovered two additional connexins, connexin40 (Cx40) and connexin45 (Cx45), that interact with CIP75. Nuclear magnetic resonance (NMR) analyses identified the direct interaction of the CIP75 UBA domain with the carboxyl-terminal (CT) domains of Cx40 and Cx45. Reduction in CIP75 by shRNA in HeLa cells expressing Cx40 or Cx45 resulted in increased levels of the connexins. Furthermore, treatment with trafficking inhibitors confirmed that both connexins undergo endoplasmic reticulum-associated degradation (ERAD), and that CIP75 preferentially interacts with the connexin proteins bound for proteasomal degradation from the ER. In addition, we have also discovered that CIP75 interacts with ER-localized Cx32 in a process that is likely mediated by Cx32 ubiquitination. Thus, we have identified novel interacting connexin proteins of CIP75, indicating a role for CIP75 in regulating the levels of connexins in general, through proteasomal degradation.
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Kopanic JL, Al-mugotir MH, Kieken F, Zach S, Trease AJ, Sorgen PL. Characterization of the connexin45 carboxyl-terminal domain structure and interactions with molecular partners. Biophys J 2014; 106:2184-95. [PMID: 24853747 PMCID: PMC4052358 DOI: 10.1016/j.bpj.2014.03.045] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2013] [Revised: 03/19/2014] [Accepted: 03/31/2014] [Indexed: 02/02/2023] Open
Abstract
Mechanisms underlying the initiation and persistence of lethal cardiac rhythms are of significant clinical and scientific interests. Gap junctions are principally involved in forming the electrical connections between myocytes, and changes in distribution, density, and properties are consistent characteristics in arrhythmic heart disease. Therefore, understanding the structure and function of gap junctions during normal and abnormal impulse propagation are essential in the control of arrhythmias. For example, Cx45 is predominately expressed in the specialized myocytes of the impulse generation and conduction system. In both ventricular and atrial human working myocytes, Cx45 is present in very low quantities. However, a reduction in Cx43 coupled with an increased Cx45 protein levels within the ventricles have been observed after myocardial infarction and end-stage heart failure. Cx45 may influence electrical and/or metabolic coupling as a result of pathophysiological overexpression. Our goal was to identify mechanisms that could cause cellular coupling to be different between the cardiac connexins. Based upon the conserved transmembrane and extracellular loop segments, our focus was on identifying features within the divergent cytoplasmic portions. Here, we biophysically characterize the carboxyl-terminal domain of Cx45 (Cx45CT). Purification revealed the possibility of oligomeric species, which was confirmed by analytical ultracentrifugation experiments. Sedimentation equilibrium and circular dichroism studies of different Cx45CT constructs identified one region of α-helical structure (A333-N361) that mediates CT dimerization through hydrophobic contacts. Interestingly, the binding affinity of Cx45CT dimerization is 1000-fold stronger than Cx43CT dimerization. Cx45CT resonance assignments were also used to identify the binding sites and affinities of molecular partners involved in the Cx45 regulation; although none disrupted dimerization, many of these proteins interacted within one intrinsically disordered region (P278-P285). This domain has similarities with other cardiac connexins, and we propose they constitute a master regulatory domain, which contains overlapping molecular partner binding, cis-trans proline isomerization, and phosphorylation sites.
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Affiliation(s)
- Jennifer L Kopanic
- Department of Biochemistry and Molecular Biology, University of Nebraska Medical Center, Omaha, Nebraska
| | - Mona H Al-mugotir
- Department of Biochemistry and Molecular Biology, University of Nebraska Medical Center, Omaha, Nebraska
| | - Fabien Kieken
- Department of Biochemistry and Molecular Biology, University of Nebraska Medical Center, Omaha, Nebraska
| | - Sydney Zach
- Department of Biochemistry and Molecular Biology, University of Nebraska Medical Center, Omaha, Nebraska
| | - Andrew J Trease
- Department of Biochemistry and Molecular Biology, University of Nebraska Medical Center, Omaha, Nebraska
| | - Paul L Sorgen
- Department of Biochemistry and Molecular Biology, University of Nebraska Medical Center, Omaha, Nebraska.
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Stauch K, Kieken F, Sorgen P. Characterization of the structure and intermolecular interactions between the connexin 32 carboxyl-terminal domain and the protein partners synapse-associated protein 97 and calmodulin. J Biol Chem 2012; 287:27771-88. [PMID: 22718765 PMCID: PMC3431650 DOI: 10.1074/jbc.m112.382572] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2012] [Revised: 06/20/2012] [Indexed: 12/20/2022] Open
Abstract
In Schwann cells, connexin 32 (Cx32) can oligomerize to form intracellular gap junction channels facilitating a shorter pathway for metabolite diffusion across the layers of the myelin sheath. The mechanisms of Cx32 intracellular channel regulation have not been clearly defined. However, Ca(2+), pH, and the phosphorylation state can regulate Cx32 gap junction channels, in addition to the direct interaction of protein partners with the carboxyl-terminal (CT) domain. In this study, we used different biophysical methods to determine the structure and characterize the interaction of the Cx32CT domain with the protein partners synapse-associated protein 97 (SAP97) and calmodulin (CaM). Our results revealed that the Cx32CT is an intrinsically disordered protein that becomes α-helical upon binding CaM. We identified the GUK domain as the minimal SAP97 region necessary for the Cx32CT interaction. The Cx32CT residues affected by the binding of CaM and the SAP97 GUK domain were determined as well as the dissociation constants for these interactions. We characterized three Cx32CT Charcot-Marie-Tooth disease mutants (R219H, R230C, and F235C) and identified that whereas they all formed functional channels, they all showed reduced binding affinity for SAP97 and CaM. Additionally, we report that in RT4-D6P2T rat schwannoma cells, Cx32 is differentially phosphorylated and exists in a complex with SAP97 and CaM. Our studies support the importance of protein-protein interactions in the regulation of Cx32 gap junction channels and myelin homeostasis.
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Affiliation(s)
- Kelly Stauch
- From the Department of Biochemistry and Molecular Biology, University of Nebraska Medical Center, Omaha, Nebraska 68198
| | - Fabien Kieken
- From the Department of Biochemistry and Molecular Biology, University of Nebraska Medical Center, Omaha, Nebraska 68198
| | - Paul Sorgen
- From the Department of Biochemistry and Molecular Biology, University of Nebraska Medical Center, Omaha, Nebraska 68198
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Bouvier D, Spagnol G, Chenavas S, Kieken F, Vitrac H, Brownell S, Kellezi A, Forge V, Sorgen PL. Characterization of the structure and intermolecular interactions between the connexin40 and connexin43 carboxyl-terminal and cytoplasmic loop domains. J Biol Chem 2009; 284:34257-71. [PMID: 19808665 PMCID: PMC2797195 DOI: 10.1074/jbc.m109.039594] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2009] [Revised: 09/10/2009] [Indexed: 11/06/2022] Open
Abstract
Gap junctions are intercellular channels that allow the passage of ions, small molecules, and second messengers that are essential for the coordination of cellular function. They are formed by two hemichannels, each constituted by the oligomerization of six connexins (Cx). Among the 21 different human Cx isoforms, studies have suggested that in the heart, Cx40 and Cx43 can oligomerize to form heteromeric hemichannels. The mechanism of heteromeric channel regulation has not been clearly defined. Tissue ischemia leads to intracellular acidification and closure of Cx43 and Cx40 homomeric channels. However, coexpression of Cx40 and Cx43 in Xenopus oocytes enhances the pH sensitivity of the channel. This phenomenon requires the carboxyl-terminal (CT) part of both connexins. In this study we used different biophysical methods to determine the structure of the Cx40CT and characterize the Cx40CT/Cx43CT interaction. Our results revealed that the Cx40CT is an intrinsically disordered protein similar to the Cx43CT and that the Cx40CT and Cx43CT can interact. Additionally, we have identified an interaction between the Cx40CT and the cytoplasmic loop of Cx40 as well as between the Cx40CT and the cytoplasmic loop of Cx43 (and vice versa). Our studies support the "particle-receptor" model for pH gating of Cx40 and Cx43 gap junction channels and suggest that interactions between cytoplasmic regulatory domains (both homo- and hetero-connexin) could be important for the regulation of heteromeric channels.
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Affiliation(s)
- Denis Bouvier
- From the Department of Biochemistry and Molecular Biology and
| | - Gaelle Spagnol
- From the Department of Biochemistry and Molecular Biology and
| | - Sylvie Chenavas
- From the Department of Biochemistry and Molecular Biology and
| | - Fabien Kieken
- From the Department of Biochemistry and Molecular Biology and
| | - Heidi Vitrac
- the Laboratoire de Chimie et Biologie des Métaux (UMR 5249), Commissariat à l'Energie Atomique, 17 rue des Martyrs, Grenoble F-38054, France
| | - Sarah Brownell
- From the Department of Biochemistry and Molecular Biology and
| | - Admir Kellezi
- the Eppley Institute for Research in Cancer and Allied Diseases, University of Nebraska Medical Center, Omaha, Nebraska 68198 and
| | - Vincent Forge
- the Laboratoire de Chimie et Biologie des Métaux (UMR 5249), Commissariat à l'Energie Atomique, 17 rue des Martyrs, Grenoble F-38054, France
| | - Paul L. Sorgen
- From the Department of Biochemistry and Molecular Biology and
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Bouvier D, Kieken F, Kellezi A, Sorgen P. Structural changes in the carboxyl terminus of the gap junction protein connexin 40 caused by the interaction with c-Src and zonula occludens-1. CELL COMMUNICATION & ADHESION 2008; 15:107-18. [PMID: 18649183 PMCID: PMC2917908 DOI: 10.1080/15419060802014347] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
Abstract
c-Src can disrupt the connexin 43 (Cx43) and zonula occludens-1 (ZO-1) interaction, leading to down-regulation of gap junction intercellular communication. Previously, the authors characterized the interaction of domains from these proteins with the carboxyl terminus of Cx43 (Cx43CT) and found that binding of the c-Src SH3 domain to Cx43CT disrupted the Cx43CT/ZO-1 PDZ-2 domain complex. Because Cx43 and Cx40 form heteromeric connexons and display similar mechanisms of pH regulation, the authors addressed whether Cx40CT interacts with these domains in a similar manner as Cx43CT. Nuclear magnetic resonance (NMR) data indicate that Cx40CT is an intrinsically disordered protein. NMR titrations determined that PDZ-2 affected the last 28 Cx40CT residues and SH3 shifted numerous amino-terminal Cx40CT residues. Finally, the Cx40CT/PDZ-2 complex was unaffected by SH3 and both domains interacted simultaneously with Cx40CT. This result differs from when the same experiment was performed with Cx43CT, suggesting different mechanisms of regulation exist between connexin isoforms, even when involving the same molecular partners.
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Affiliation(s)
- Denis Bouvier
- Department of Biochemistry and Molecular Biology, University of Nebraska Medical Center, Omaha, NE 68198
| | - Fabien Kieken
- Department of Biochemistry and Molecular Biology, University of Nebraska Medical Center, Omaha, NE 68198
| | - Admir Kellezi
- Department of Biochemistry and Molecular Biology, University of Nebraska Medical Center, Omaha, NE 68198
| | - Paul Sorgen
- Department of Biochemistry and Molecular Biology, University of Nebraska Medical Center, Omaha, NE 68198
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