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Modulator - Issue No. 25

In Focus: Connexin and Pannexin Gap Junction Channels

Gap junctions are usually found in clusters and enable intercellular communication by allowing the passage of small molecules between cells2. They play important roles in different biological processes. These include differentiation, cell cycle synchronization, cellular development, neuronal activity and the immune response5,7,9.

Proteins involved in gap junction formation are composed of four transmembrane domains, two extracellular loops and one intracellular loop and intracellular N- and C-termini10,12. Several consensus cysteine residues in the extracellular loop are essential and necessary for intercellular docking of gap junction hemichannels in the opposing cell membrane3,10,12.

Connexins (Cx) include 21 integral membrane proteins belonging to this family and form homomeric or heteromeric hexamers generally termed connexons or hemi-channels. In turn, these hemi-channels further assemble in a head-to-head manner, thus forming gap junction channels4,7. Connexins are ubiquitously expressed and their activity is regulated at the expression level and by post-translational modifications4.

Due to their important roles, mutations in connexins are linked to a number of diseases such as neurodegenerative disorders, skin diseases and developmental abnormalities5,7,11.

Pannexins (Pannexin 1, Pannexin 2 and Pannexin 3) also belong to the superfamily of gap junction proteins. Pannexin 1 (PANX1) is ubiquitously expressed, Pannexin 2 (PANX2) is specifically expressed in the human brain and widespread in rodents and Pannexin 3 (PANX3) is also detected in the brain8.

The gating properties of Pannexins were studied in Xenopus oocytes and results indicate that only PANX1 is able to form homomeric hemichannels, and is also able to form heteromeric hemichannels with PANX2 but not with PANX31,6. Not surprising, PANX1 gating properties depend whether it forms homomeric or heteromeric hemichannels.

A number of different stimuli are known to open these channels and include mechanical stress, extracellular ATP, increases in intracellular Ca2+ and inflammation6.

Possible roles for Pannexins include paracrine signaling in vascular endothelial cells and taste cell signaling6.

Alomone Labs is pleased to offer highly specific antibodies against the following gap junction channels: Anti-Connexin-26 (GJB2) Antibody (#ACC-212), Anti-Connexin-32 Antibody (#ACC-211), Anti-Connexin-43 Antibody (ACC-201) and Anti-Pannexin 2 (extracellular) Antibody (#ACC-232). They can be used in a number of applications such as western blot analysis and immunocytochemistry.

Gap junctions are usually found in clusters and enable intercellular communication by allowing the passage of small molecules between cells2. They play important roles in different biological processes. These include differentiation, cell cycle synchronization, cellular development, neuronal activity and the immune response5,7,9.

Proteins involved in gap junction formation are composed of four transmembrane domains, two extracellular loops and one intracellular loop and intracellular N- and C-termini10,12. Several consensus cysteine residues in the extracellular loop are essential and necessary for intercellular docking of gap junction hemichannels in the opposing cell membrane3,10,12.

Connexins (Cx) include 21 integral membrane proteins belonging to this family and form homomeric or heteromeric hexamers generally termed connexons or hemi-channels. In turn, these hemi-channels further assemble in a head-to-head manner, thus forming gap junction channels4,7. Connexins are ubiquitously expressed and their activity is regulated at the expression level and by post-translational modifications4.

Due to their important roles, mutations in connexins are linked to a number of diseases such as neurodegenerative disorders, skin diseases and developmental abnormalities5,7,11.

Pannexins (Pannexin 1, Pannexin 2 and Pannexin 3) also belong to the superfamily of gap junction proteins. Pannexin 1 (PANX1) is ubiquitously expressed, Pannexin 2 (PANX2) is specifically expressed in the human brain and widespread in rodents and Pannexin 3 (PANX3) is also detected in the brain8.

The gating properties of Pannexins were studied in Xenopus oocytes and results indicate that only PANX1 is able to form homomeric hemichannels, and is also able to form heteromeric hemichannels with PANX2 but not with PANX31,6. Not surprising, PANX1 gating properties depend whether it forms homomeric or heteromeric hemichannels.

A number of different stimuli are known to open these channels and include mechanical stress, extracellular ATP, increases in intracellular Ca2+ and inflammation6.

Possible roles for Pannexins include paracrine signaling in vascular endothelial cells and taste cell signaling6.

Alomone Labs is pleased to offer highly specific antibodies against the following gap junction channels: Anti-Connexin-26 (GJB2) Antibody (#ACC-212), Anti-Connexin-32 Antibody (#ACC-211), Anti-Connexin-43 Antibody (ACC-201) and Anti-Pannexin 2 (extracellular) Antibody (#ACC-232). They can be used in a number of applications such as western blot analysis and immunocytochemistry.

References
1. Bruzzone, R. et al. (2003) Proc. Natl. Acad. Sci. U.S.A. 100, 13644.
2. Chew, S.S. et al. (2010) Exp. Neurol. 225, 250.
3. Falk, M.M. (2000) Eur. J. Cell. Biol. 79, 564.
4. Goodenough, D.A. and Paul, D.L. (2011) Cold Spring Harb. Persp. Biol. 2009, 1.
5. Hu, X. et al. (2006) Biophys. J. 90, 140.
6. Litvin, O. et al. (2006) J. Cell. Mol. Med. 10, 613.
7. Nakagawa, S. et al. (2010) Curr. Opin. Struct. Biol. 20, 423.
8. Panchin, Y.V. (2005) J. Exp. Biol. 208, 1415.
9. Trexter, E.B. et al. (1996) Proc. Natl. Acad. Sci. U.S.A. 93, 5836.
10. Shestopalov, V.I. and Panchin, Y. (2008) Cell. Mol. Life Sci. 65, 376.
11. Tang, Q. et al. (2009) J. Gen. Physiol. 133, 555.
12. Unger, V.M. et al. (1999) Science 283, 1176.