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Contributed by Jennifer Lippincott-Schwartz, September 9, 2013 (sent for review June 20, 2013)
Significance
We used 3D Bessel beam plane illumination and spinning disk microscopy to reveal fast structural changes in the architecture of gap junctions (GJs). Previously, GJ plaques were considered relatively stable structures. We demonstrate extremely rapid remodeling of proteins and lipids within GJ plaques in response to bacterial toxin exposure. Connexin channels within GJ plaques undergo dramatic rearrangements that lead to increased connexin packing and lipid reorganization. These changes likely reflect lipid-phase separation events in the biological membrane. Toxin-induced connexin reorganization depends on lipids and is little modified by membrane–cytoskeletal interactions. We suggest that fast GJ changes upon toxin exposure reveal an early-response system of cells and that GJ plaques are much more dynamic structures than previously recognized.
Abstract
Gap junctions (GJs) represent connexin-rich membrane domains that connect interiors of adjoining cells in mammalian tissues. How fast GJs can respond to bacterial pathogens has not been known previously. Using Bessel beam plane illumination and confocal spinning disk microscopy, we found fast (∼500 ms) formation of connexin-depleted regions (CDRs) inside GJ plaques between cells exposed to AB5 toxins. CDR formation appears as a fast redistribution of connexin channels within GJ plaques with minor changes in outline or geometry. CDR formation does not depend on membrane trafficking or submembrane cytoskeleton and has no effect on GJ conductance. However, CDR responses depend on membrane lipids, can be modified by cholesterol-clustering agents and extracellular K+ ion concentration, and influence cAMP signaling. The CDR response of GJ plaques to bacterial toxins is a phenomenon observed for all tested connexin isoforms. Through signaling, the CDR response may enable cells to sense exposure to AB5 toxins. CDR formation may reflect lipid-phase separation events in the biological membrane of the GJ plaque, leading to increased connexin packing and lipid reorganization. Our data demonstrate very fast dynamics (in the millisecond-to-second range) within GJ plaques, which previously were considered to be relatively stable, long-lived structures.
Footnotes
- ↵1To whom correspondence may be addressed. E-mail: irina.majoul{at}bio.uni-luebeck.de, lippincj{at}mail.nih.gov, or duden{at}bio.uni-luebeck.de.
Author contributions: I.V.M., F.B., and R.D. designed research; I.V.M., L.G., F.B., and R.D. performed research; I.V.M., L.G., E. Betzig, D.O., E. Butkevich, Y.K., F.B., and J.L.-S. contributed new reagents/analytic tools; I.V.M., L.G., E. Betzig, D.O., E. Butkevich, Y.K., F.B., M.V.L.B., J.L.-S., and R.D. analyzed data; and I.V.M., D.O., F.B., M.V.L.B., J.L.-S., and R.D. wrote the paper.
The authors declare no conflict of interest.
This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1315850110/-/DCSupplemental.
Freely available online through the PNAS open access option.
Structural responses of gap junctions to AB5 toxin
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