Open AccessThe Gap‐Junction Protein Connexin 56 is Phosphorylated in the Intracellular Loop and the Carboxy‐Terminal Region
Author(s) -
Berthoud Viviana M.,
Beyer Eric C.,
Kurata Wendy E.,
Lau Alan F.,
Lampe Paul D.
Publication year - 1997
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1111/j.1432-1033.1997.00089.x
Subject(s) - connexin , phosphorylation , forskolin , protein phosphorylation , protein kinase a , biology , microbiology and biotechnology , kinase , biochemistry , chemistry , gap junction , intracellular , in vitro
The lens gap‐junction protein, connexin 56, is modified by phosphorylation. Two‐dimensional mapping of tryptic phosphopeptides of 32 P‐labeled connexin 56 from primary chicken‐lens cultures showed that treatment with 12‐ O ‐tetradecanoylphorbol 13‐acetate (TPA) induced an increase in phosphorylation of connexin 56 at specific constitutively phosphorylated sites. Treatment with 8‐Br‐cAMP or forskolin did not induce substantial changes in connexin 56 phosphorylation. Two phosphorylation sites within connexin 56, S493 and S118, were identified after HPLC purification and peptide sequencing of tryptic phosphopeptides from bacterially expressed connexin 56 fusion proteins phosphorylated by protein kinase C or protein kinase A in vitro. Comparisons of the two‐dimensional maps of tryptic phosphopeptides from in vitro phosphorylated connexin 56 fusion proteins and in vivo phosphorylated connexin 56 showed that S493 and S118 were constitutively phosphorylated in lentoid‐containing cultures, and that treatment with TPA induced an increase in phosphorylation of the peptides containing S118. It is suggested that phosphorylation of connexin 56 at S118 is involved in the TPA‐induced decrease in intercellular communication and acceleration of connexin 56 degradation.