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The Journal of Neuroscience, May 15, 1999, 19(10):3752-3760
Altered Formation of Hemichannels and Gap Junction Channels
Caused by C-Terminal Connexin-32 Mutations
Carmen
Castro1,
Juan M.
Gómez-Hernandez1,
Kaisa
Silander2, and
Luis C.
Barrio1
1 Unidad de Neurología Experimental-Consejo
Superior de Investigaciones Científicas, Departamento de
Investigación, Hospital "Ramón y Cajal," 28034 Madrid,
Spain, and 2 Deparment of Medical Genetics, University of
Turku, FIN-20520 Turku, Finland
Hexamers of connexins (Cxs) form hemichannels that dock tightly in
series via their extracellular domains to give rise to gap junction
channels. Here we examined the ability of a variety of C-terminal Cx32
mutations, most of which have been identified in X-linked
Charcot-Marie-Tooth disease, to form hemichannels and to complete gap
junction channels using the Xenopus oocyte system.
First, we show that undocked wild-type Cx32 hemichannels at the plasma
membrane can be detected as opening channels activated by
depolarization. We have been able to estimate the efficiency of
assembly of complete channels by measuring the time-dependent incorporation of preformed hemichannels into gap junction channels after cell-to-cell contact. These data offer strong evidence that hemichannels are the direct precursors of gap junction channels. Of 11 Cx32 mutants tested, a group of 5 mutations prevented the formation of
functional hemichannels at the cell surface, whereas 4 mutations were
fully able to form precursors but reduced the ability of hemichannels
to assemble into complete channels, and 2 mutants formed channels
normally. The data revealed that a minimum length of human Cx32
including the residue Arg-215 is required for the expression of
hemichannels at the cell surface and that the efficiency of hemichannel
incorporation into complete channels decreased gradually with the
progressive shortening of the cytoplasmic C-terminal domain.
Key words:
connexin; voltage gating; gap junction channel formation; hereditary motor sensory neuropathy; X-linked Charcot-Marie-Tooth
disease; Xenopus oocyte
Copyright © 1999 Society for Neuroscience 0270-6474/99/19103752-09$05.00/0
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