Connexons Coupling to Gap Junction Channel: Potential Role for Extracellular Protein Stabilization Centers

Connexin (Cx) proteins establish intercellular gap junction channels (Cx GJCs) through coupling of two apposed hexameric Cx hemichannels (Cx HCs, connexons). Pre- and post-GJ interfaces consist of extracellular EL1 and EL2 loops, each with three conserved cysteines. Previously, we reported that known peptide inhibitors, mimicking a variety of Cx43 sequences, appear non-selective when binding to homomeric Cx43 vs. Cx36 GJC homology model subtypes. In pursuit of finding potentially Cx subtype-specific inhibitors of connexon-connexon coupling, we aimed at to understand better how the GJ interface is formed. Here we report on the discovery of Cx GJC subtype-specific protein stabilization centers (SCs) featuring GJ interface architecture. First, the Cx43 GJC homology model, embedded in two opposed membrane bilayers, has been devised. Next, we endorsed the fluctuation dynamics of SCs of the interface domain of Cx43 GJC by applying standard molecular dynamics under open and closed cystine disulfide bond (CS-SC) preconditions. The simulations confirmed the major role of of the unique trans-GJ SC pattern comprising conserved (55N, 56T) and non-conserved (57Q) residues of the apposed EL1 loops in the stabilization of the GJC complex. Importantly, clusters of SC patterns residing close to the GJ interface domain appear to orient the interface formation via the numerous SCs between EL1 and EL2. These include central 54CS-S198C or 61CS-S192C contacts with residues 53R, 54C, 55N, 197D, 199F or 64V, 191P, respectively. In addition, we revealed that GJC interface formation is favoured when the psi dihedral angle of the nearby 193P residue is stable around 180° and the interface SCs disappear when this angle moves to the 0° to −45° range. The potential of the association of non-conserved residues with SC motifs in connexon-connexon coupling makes the development of Cx subtype-specific inhibitors viable.

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Role of Gap Junctions and Hemichannels in Parasitic Infections

BioMed Research International ◽

10.1155/2013/589130 ◽

2013 ◽

Vol 2013 ◽

pp. 1-17 ◽

Cited By ~ 9

Author(s):

José Luis Vega ◽

Mario Subiabre ◽

Felipe Figueroa ◽

Kurt Alex Schalper ◽

Luis Osorio ◽

...

Keyword(s):

Gap Junction ◽

Viral Infections ◽

Cellular Communication ◽

Parasitic Infections ◽

Pathological State ◽

Channel Changes ◽

Gap Junction Channels ◽

Gap Junction Channel ◽

Relevant Role

In vertebrates, connexins (Cxs) and pannexins (Panxs) are proteins that form gap junction channels and/or hemichannels located at cell-cell interfaces and cell surface, respectively. Similar channel types are formed by innexins in invertebrate cells. These channels serve as pathways for cellular communication that coordinate diverse physiologic processes. However, it is known that many acquired and inherited diseases deregulate Cx and/or Panx channels, condition that frequently worsens the pathological state of vertebrates. Recent evidences suggest that Cx and/or Panx hemichannels play a relevant role in bacterial and viral infections. Nonetheless, little is known about the role of Cx- and Panx-based channels in parasitic infections of vertebrates. In this review, available data on changes in Cx and gap junction channel changes induced by parasitic infections are summarized. Additionally, we describe recent findings that suggest possible roles of hemichannels in parasitic infections. Finally, the possibility of new therapeutic designs based on hemichannel blokers is presented.

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Gap Junction Channelopathies and Calmodulinopathies. Do Disease-Causing Calmodulin Mutants Affect Direct Cell–Cell Communication?

International Journal of Molecular Sciences ◽

10.3390/ijms22179169 ◽

2021 ◽

Vol 22 (17) ◽

pp. 9169

Author(s):

Camillo Peracchia

Keyword(s):

Gap Junction ◽

Genetic Diseases ◽

Channel Gating ◽

Cell Communication ◽

Potential Effect ◽

Gap Junction Channel ◽

Direct Cell ◽

Connexin Genes ◽

Cell Cell

The cloning of connexins cDNA opened the way to the field of gap junction channelopathies. Thus far, at least 35 genetic diseases, resulting from mutations of 11 different connexin genes, are known to cause numerous structural and functional defects in the central and peripheral nervous system as well as in the heart, skin, eyes, teeth, ears, bone, hair, nails and lymphatic system. While all of these diseases are due to connexin mutations, minimal attention has been paid to the potential diseases of cell–cell communication caused by mutations of Cx-associated molecules. An important Cx accessory protein is calmodulin (CaM), which is the major regulator of gap junction channel gating and a molecule relevant to gap junction formation. Recently, diseases caused by CaM mutations (calmodulinopathies) have been identified, but thus far calmodulinopathy studies have not considered the potential effect of CaM mutations on gap junction function. The major goal of this review is to raise awareness on the likely role of CaM mutations in defects of gap junction mediated cell communication. Our studies have demonstrated that certain CaM mutants affect gap junction channel gating or expression, so it would not be surprising to learn that CaM mutations known to cause diseases also affect cell communication mediated by gap junction channels.

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Chimeric evidence for a role of the connexin cytoplasmic loop in gap junction channel gating

Pflügers Archiv - European Journal of Physiology ◽

10.1007/s004240050076 ◽

1996 ◽

Vol 431 (6) ◽

pp. 844-852 ◽

Cited By ~ 41

Author(s):

Xiaoguang Wang ◽

Liqiong Li ◽

Lillian L. Peracchia ◽

Camillo Peracchia

Keyword(s):

Gap Junction ◽

Channel Gating ◽

Cytoplasmic Loop ◽

Gap Junction Channel

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Structure of the Ductin Channel

Bioscience Reports ◽

10.1023/a:1020205231507 ◽

1998 ◽

Vol 18 (6) ◽

pp. 287-297 ◽

Cited By ~ 10

Author(s):

Malcolm E. Finbow ◽

John D. Pitts

Keyword(s):

Gap Junctions ◽

Gap Junction ◽

Cell Movement ◽

Large Family ◽

Structural Data ◽

Proton Pumps ◽

Gap Junction Channel ◽

Essential Components ◽

Resolution Model

Gap junctions appear to be essential components of metazoan animals providing a means of direct means of communication between neighboring cells. They are sieve-like structures which allow cell–cell movement of cytosolic solutes below 1000 MW. The major role of gap junctions would appear to be homeostatic giving rise to groups of cells which act as functional units. Ductin is the major core component of gap junctions and recent structural data shows it to be a four alpha-helical bundle which fits particularly well into a low resolution model of the gap junction channel. Ductin is also the main membrane component of the vacuolar H+-ATPase that is found in all eukaryotes and it seems likely that the gap junction channel first evolved as a housing for the rotating spindle of these proton pumps. Because ductin protrudes little from the membrane, other proteins are required to bring cell surfaces close enough together to form gap junctions. Such proteins may include connexins, a large family of proteins found in vertebrates.

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Role of Gap Junction Channel in the Development of Beat-to-Beat Action Potential Repolarization Variability and Arrhythmias

Current Pharmaceutical Design ◽

10.2174/1381612820666141029102443 ◽

2014 ◽

Vol 21 (8) ◽

pp. 1042-1052 ◽

Cited By ~ 8

Author(s):

Janos Magyar ◽

Tamas Banyasz ◽

Norbert Szentandrassy ◽

Kornel Kistamas ◽

Peter Nanasi ◽

...

Keyword(s):

Action Potential ◽

Gap Junction ◽

Gap Junction Channel ◽

Action Potential Repolarization

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Chimeric evidence for a role of the connexin cytoplasmic loop in gap junction channel gating

Pflügers Archiv - European Journal of Physiology ◽

10.1007/bf02332168 ◽

1996 ◽

Vol 431 (S6) ◽

pp. 844-852 ◽

Cited By ~ 3

Author(s):

Xiaoguang Wang ◽

Liqiong Li ◽

Lillian L. Peracchia ◽

Camillo Peracchia

Keyword(s):

Gap Junction ◽

Channel Gating ◽

Cytoplasmic Loop ◽

Gap Junction Channel

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Molecular dissection of a basic COOH-terminal domain of Cx32 that inhibits gap junction gating sensitivity

AJP Cell Physiology ◽

10.1152/ajpcell.1998.275.5.c1384 ◽

1998 ◽

Vol 275 (5) ◽

pp. C1384-C1390 ◽

Cited By ~ 17

Author(s):

Xiao Guang Wang ◽

Camillo Peracchia

Keyword(s):

Gap Junction ◽

Electrostatic Interactions ◽

Xenopus Oocytes ◽

Voltage Sensitivity ◽

Wild Type ◽

Cytoplasmic Loop ◽

Terminal Domain ◽

Gap Junction Channel ◽

Chemical Gating

Connexin32 (Cx32) mutants were studied by double voltage clamp in Xenopus oocytes to determine the role of basic COOH-terminal residues in gap junction channel gating by CO2 and transjunctional voltage. Replacement of five arginines with N (5R/N) or T residues in the initial COOH-terminal domain (CT1) of Cx32 enhanced CO2 sensitivity. The positive charge, rather than the R residue per se, is responsible for the inhibitory role of CT1, because mutants replacing the five R residues with K (5R/K) or H (5R/H) displayed CO2 sensitivity comparable to that of wild-type Cx32. Mutants replacing R with N residues four at a time (4R/N) showed that CO2 sensitivity is strongly inhibited by R215 and mildly by R219, whereas R220, R223, and R224 may slightly increase sensitivity. Neither the 5R/N nor the 4R/N mutants differed in voltage sensitivity from wild-type Cx32. The possibility that inhibition of gating sensitivity results from electrostatic interactions between CT1 and the cytoplasmic loop is discussed as part of a model that envisions the cytoplasmic loop of Cx32 as a key element of chemical gating.

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