Hetero-domain interactions as a mechanism for the regulation of connexin channels.
Previous studies have shown that chemical regulation of connexin43 (Cx43) depends on the presence of the carboxyl terminal (CT) domain. A particle-receptor (or "ball-and-chain") model has been proposed to explain the mechanism of gating. We tested whether the CT region behaved as a functional domain for other members of the connexin family. The pH sensitivity of wild-type and Ct-truncated connexins was quantified by use of electrophysiological and optical techniques and the Xenopus oocyte system. The CT domain of Cx45 had no role in pH regulation, although a partial role was shown for Cx37 and Cx50. A prominent effect was observed for Cx40 and Cx43. In addition, we found that the CT domain of Cx40 that was expressed as a separate fragment rescued the pH sensitivity of the truncated Cx40 (Cx40tr), which was in agreement with a particle-receptor model. Because Cx40 and Cx43 often colocalize and possibly heteromerize, we tested the pH sensitivity of Cx40tr when coexpressed with the CT domain of Cx43 (hetero-domain interactions). We found that the CT domain of Cx43 enhanced the pH sensitivity of Cx40tr; similarly, the CT domain of Cx40 restored the pH sensitivity of the truncated Cx43. In addition, the CT domain of Cx43 granted insulin sensitivity to the otherwise insulin-insensitive Cx26 or Cx32 channels. These data show that the particle-receptor model is preserved in Cx40 and the regulatory domain of one connexin can specifically interact with a channel formed by another connexin. Hetero-domain interactions could be critical for the regulation of heteromeric channels.
Stergiopoulos
K
K
Department of Pharmacology, SUNY Health Science Center, Syracuse, NY 13210, USA.
Alvarado
J L
JL
Mastroianni
M
M
Ek-Vitorin
J F
JF
Taffet
S M
SM
Delmar
M
M
D000136:Acid-Base Equilibrium / Q000502:physiology*; D000818:Animals; D001692:Biological Transport / Q000187:drug effects / Q000502:physiology; D000072259:Connexin 26; D017630:Connexins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D005136:Eye Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D015870:Gene Expression / Q000502:physiology; D006863:Hydrogen-Ion Concentration; D007004:Hypoglycemic Agents / Q000494:pharmacology; D007328:Insulin / Q000494:pharmacology; D015640:Ion Channel Gating / Q000502:physiology; D008969:Molecular Sequence Data; D009865:Oocytes / Q000502:physiology; D017434:Protein Structure, Tertiary; D012333:RNA, Messenger / Q000032:analysis; D017386:Sequence Homology, Amino Acid; D014981:Xenopus; D000097002:Gap Junction beta-1 Protein; D000097003:Gap Junction alpha-5 Protein; D000097006:Gap Junction alpha-4 Protein; D000099264:Connexin 50
D000072259:Connexin 26; D017630:Connexins; D005136:Eye Proteins; D007004:Hypoglycemic Agents; D007328:Insulin; D012333:RNA, Messenger; D000097002:Gap Junction beta-1 Protein; D000097003:Gap Junction alpha-5 Protein; D000097006:Gap Junction alpha-4 Protein; D000099264:Connexin 50; C000607045:GJB2 protein, Xenopus; C082917:GJA3 protein, human