Cx29 and Cx32, two connexins expressed by myelinating glia, do not interact and are functionally distinct.
In rodents, oligodendrocytes and myelinating Schwann cells express connexin32 (Cx32) and Cx29, which have different localizations in the two cell types. We show here that, in contrast to Cx32, Cx29 does not form gap junction plaques or functional gap junctions in transfected cells. Furthermore, when expressed together, Cx29 and Cx32 are not colocalized and do not coimmunoprecipitate. To determine the structural basis of their divergent behavior, we generated a series of chimeric Cx32-Cx29 proteins by exchanging their intracellular loops and/or their C-terminal cytoplasmic tails. Although some chimerae reach the cell membrane, others appear to be largely localized intracellularly; none form gap junction plaques or functional gap junctions. Substituting the C-terminus or the intracellular loop and the C-terminus of Cx32 with those of Cx29 does not disrupt their colocalization or coimmunoprecipitation with Cx32. Substituting the C-terminus of Cx29 with that of Cx32 does not disrupt the coimmunoprecipitation or the colocalization with Cx29, whereas substituting both the intracellular loop and the C-terminus of Cx32 with those of Cx29 diminishes the coimmunoprecipitation with Cx29. Conversely, the Cx32 chimera that contains the intracellular loop of Cx29 coimmunoprecipitates with Cx29, indicating that the intracellular loop participates in Cx29-Cx29 interactions. These data indicate that homomeric interactions of Cx29 and especially Cx32 largely require other domains: the N-terminus, transmembrane domains, and extracellular loops. Substituting the intracellular loop and/or tail of Cx32 with those of Cx29 appears to prevent Cx32 from forming functional gap junctions.
Ahn
Meejin
M
Department of Neurology, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104-6077, USA.
Lee
Jonathan
J
Gustafsson
Andreas
A
Enriquez
Alan
A
Lancaster
Eric
E
Sul
Jai-Yoon
JY
Haydon
Philip G
PG
Paul
David L
DL
Huang
Yan
Y
Abrams
Charles K
CK
Scherer
Steven S
SS
D000818:Animals; D019556:COS Cells; D002454:Cell Differentiation / Q000235:genetics; D002462:Cell Membrane / Q000378:metabolism / Q000648:ultrastructure; D002522:Chlorocebus aethiops; D017630:Connexins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D017629:Gap Junctions / Q000378:metabolism / Q000648:ultrastructure; D006367:HeLa Cells; D006801:Humans; D051379:Mice; D050506:Mutant Chimeric Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D009186:Myelin Sheath / Q000378:metabolism* / Q000648:ultrastructure; D009419:Nerve Tissue Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D009420:Nervous System / Q000254:growth & development* / Q000378:metabolism* / Q000648:ultrastructure; D009457:Neuroglia / Q000378:metabolism* / Q000648:ultrastructure; D017434:Protein Structure, Tertiary / Q000502:physiology; D000097002:Gap Junction beta-1 Protein
D017630:Connexins; D050506:Mutant Chimeric Proteins; D009419:Nerve Tissue Proteins; D000097002:Gap Junction beta-1 Protein; C464673:Gje1 protein, mouse