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Interaction between connexin35 and zonula occludens-1 and its potential role in the regulation of electrical synapses.

ABSTRACT: Although regulation of chemical transmission is known to involve the interaction of receptors with scaffold proteins, little is known about the existence of protein-protein interactions in regulating gap junction-mediated electrical synapses. The scaffold protein zonula-occludens-1 (ZO-1), a member of the MAGUK family of proteins, was reported to interact with several connexins (Cxs). We show here that ZO-1 extensively colocalizes with Cx35 at identifiable "mixed" (electrical and chemical) contacts on goldfish Mauthner cells, a model synapse for the study of vertebrate electrical transmission where it is possible to correlate physiological properties with molecular composition. Further, our analysis indicates that these proteins directly interact at goldfish electrical synapses. In contrast to Cx43, which interacts with ZO-1 via the PDZ2 domain, Cx35 interacts with ZO-1 via the PDZ1 domain, and this association is of lower affinity. The properties of the ZO-1/Cx35 association suggest the existence of a more dynamic relation between these two proteins, possibly including a role of ZO-1 in regulating gap junctional conductance at these highly modifiable electrical synapses. The interaction of ZO-1 with conserved regions of the C termini of Cx35/Cx36 orthologs may have a common function at electrical synapses of mammals and other vertebrates.

SUBMITTER: Flores CE

PROVIDER: S-EPMC2527948 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Most gap junctions between neurons in mammalian retina contain abundant connexin36, often in association with the scaffolding protein zonula occludens-1. We now investigate co-association of connexin36, zonula occludens-1, zonula occludens-2 and Y-box transcription factor 3 (zonula occludens-1-associated nucleic acid-binding protein) in mouse and rat retina. By immunoblotting, zonula occludens-1-associated nucleic acid-binding protein and zonula occludens-2 were both detected in retina, and zonula occludens-2 in retina was found to co-immunoprecipitate with connexin36. By immunofluorescence, the four proteins appeared as puncta distributed in the plexiform layers. In the inner plexiform layer, most connexin36-puncta were co-localized with zonula occludens-1, and many were co-localized with zonula occludens-1-associated nucleic acid-binding protein. Moreover, zonula occludens-1-associated nucleic acid-binding protein was often co-localized with zonula occludens-1. Nearly all zonula occludens-2-puncta were positive for connexin36, zonula occludens-1 and zonula occludens-1-associated nucleic acid-binding protein. In the outer plexiform layer, connexin36 was also often co-localized with zonula occludens-1-associated nucleic acid-binding protein. In connexin36 knockout mice, labeling of zonula occludens-1 was slightly reduced in the inner plexiform layer, zonula occludens-1-associated nucleic acid-binding protein was decreased in the outer plexiform layer, and both zonula occludens-1-associated nucleic acid-binding protein and zonula occludens-2 were markedly decreased in the inner sublamina of the inner plexiform layer, whereas zonula occludens-1, zonula occludens-2 and zonula occludens-1-associated nucleic acid-binding protein puncta persisted and remained co-localized in the outer sublamina of the inner plexiform layer. By freeze-fracture replica immunogold labeling, connexin36 was found to be co-localized with zonula occludens-2 within individual neuronal gap junctions. In addition, zonula occludens-1-associated nucleic acid-binding protein was abundant in a portion of ultrastructurally-defined gap junctions throughout the inner plexiform layer, and some of these junctions contained both connexin36 and zonula occludens-1-associated nucleic acid-binding protein. These distinct patterns of connexin36 association with zonula occludens-1, zonula occludens-2 and zonula occludens-1-associated nucleic acid-binding protein in different sublaminae of retina, and differential responses of these proteins to connexin36 gene deletion suggest differential regulatory and scaffolding roles of these gap junction accessory proteins. Further, the persistence of a subpopulation of zonula occludens-1/zonula occludens-2/zonula occludens-1-associated nucleic acid-binding protein co-localized puncta in the outer part of the inner plexiform layer of connexin36 knockout mice suggests close association of these proteins with other structures in retina, possibly including gap junctions composed of an as-yet-unidentified connexin.

Project description:BackgroundWe previously showed that zonula occludens toxin (Zot) encoded by Campylobacter concisus zot (808T) gene has the potential to initiate inflammatory bowel disease. This Zot protein caused prolonged intestinal epithelial barrier damage, induced intestinal epithelial and macrophage production of tumor necrosis factor-α and enhanced the responses of macrophages to other microbes. In order to understand the potential virulence of Zot proteins in other Campylobacter species, in this study we examined their presence, similarities, motifs and prophages.MethodsThe presence of Zot proteins in Campylobacter species was examined by searching for the Zot family domain in multiple protein databases. Walker A and Walker B motifs in Zot proteins were identified using protein sequence alignment. A phylogenetic tree based on Campylobacter zot genes was constructed using maximum-likelihood method. Campylobacter Zot proteins were compared using protein sequence alignment. The zot-containing prophages in Campylobacter species were identified and compared with known prophage proteins and other viral proteins using protein sequence alignment and protein BLAST.ResultsTwelve Zot proteins were found in nine Campylobacter species/subspecies. Among these Campylobacter species, three species had two Zot proteins and the remaining six species/subspecies had one Zot protein. Walker A and Walker B motifs and a transmembrane domain were found in all identified Campylobacter Zot proteins. The twelve Campylobacter zot genes from the nine Campylobacter species/subspecies formed two clusters. The ZotCampyType_1 proteins encoded by Cluster 1 Campylobacter zot genes showed high similarities to each other. However, ZotCampyType_2 proteins encoded by Cluster 2 Campylobacter zot genes were more diverse. Furthermore, the zot-containing Campylobacter prophages were identified.ConclusionThis study reports the identification of two types of Campylobacter Zot proteins. The high similarities of ZotCampyType_1 proteins suggest that they are likely to have similar virulence. ZotCampyType_2 proteins are less similar to each other and their virulent properties, if any, remain to be examined individually.

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Interaction between connexin35 and zonula occludens-1 and its potential role in the regulation of electrical synapses.

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