Master of Science
Physiology and Pharmacology
Connexins are ubiquitous transmembrane proteins that assemble to form intercellular channels, called gap junctions (GJs). The amino terminal (NT) domain and residues within this domain have been shown to be important for both Vj-gating and single channel conductance (γj) of several GJs including Cx46 and Cx50. High-resolution structures of Cx46 and Cx50 GJs were recently resolved showing that NT domain folds into the inner pore where hydrophobic residues are packed against M1/2 domains stabilizing open-state conformation. We studied functional properties of GJs formed by several point variants at NT (Cx46 L10I, N13E, A14V, Q15N and Cx50 I10L, E13N, V14A, N15Q) and M2 domain (Cx50 S89T) in GJ-deficient N2A cells. We found that these variants formed functional GJs except Cx50 S89T. Altered coupling conductance, γj, and/or Vj-gating observed in GJs of L10I and A14V indicate these hydrophobic residues are important for Vj-gating and γj of these and possibly other GJs.
Summary for Lay Audience
Our body cells communicate via various mechanisms to maintain organ functioning and tissue homeostasis. One of these mechanisms is gap junction channels (GJs), which is composed of 12 connexin proteins, mediating transfer of ions and other molecules between two adjacent cells. Connexins vary in amino acids composition and thus makes different GJs with unique properties. One part of the connexin, called the amino terminal (NT) domain, folds in the channel pore acting as a physical barrier to the permeating ions and molecules. Changing the amino acid composition of the NT domain had been shown to alter channel properties. However, how NT domain regulates channel function is still not fully determined. Recent structural studies provided novel high-resolution structure models of lens connexin46 and connexin50 gap junctions. The new structures indicate that NT domain is anchored to other domains via a few NT amino acid residues showed hydrophobic properties, including those at 10th and 14th positions in these two connexins. To test these and other different amino acid residues in these lens connexins on their gap junction properties, we studied effect of switching these residues one at a time on its gap junction permeation and opening/closing controls. Our results indicate that hydrophobic residues in the NT domain could also play an important role in control gap junction ion permeation and open/close regulation as suggested by the structure models. Our study combines structural and functional studies to illustrate the mechanisms of how the NT domain shapes channel properties in these gap junction channels
Jaradat, Roa'a, "The Hydrophobic Residues in Amino Terminal Domains of Cx46 and Cx50 are Important for their Gap Junction Channel Ion Permeation and Gating" (2022). Electronic Thesis and Dissertation Repository. 8553.
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Available for download on Monday, January 01, 2024