Molecular Characterization of an Anchor Protein (AKAPCE) That Binds the RI Subunit (RCE) of Type I Protein Kinase A from Caenorhabditis elegans*
- From the Department of Molecular Pharmacology, Atran Laboratories, Albert Einstein College of Medicine, Bronx, New York 10461
Abstract
Classical A kinase anchor proteins (AKAPs) preferentially tether type II protein kinase A (PKAII) isoforms to sites in the cytoskeleton and organelles. It is not known if distinct proteins selectively sequester regulatory (R) subunits of type I PKAs, thereby diversifying functions of these critical enzymes. InCaenorhabditis elegans, a single type I PKA mediates all aspects of cAMP signaling. We have discovered a cDNA that encodes a binding protein (AKAPCE) for the regulatory subunit (RCE) of C. elegans PKAICE. AKAPCE is a novel, highly acidic RING finger protein composed of 1,280 amino acids. It binds RI-like RCE with high affinity and neither RIIα nor RIIβ competitively inhibits formation of AKAPCE·RCE complexes. The RCE-binding site was mapped to a segment of 20 amino acids in an N-terminal region of AKAPCE. Several hydrophobic residues in the binding site align with essential Leu and Ile residues in the RII-selective tethering domain of prototypic mammalian AKAPs. However, the RCE-binding region in AKAPCEdiverges sharply from consensus RII-binding sites by inclusion of three aromatic amino acids, exclusion of a highly conserved Leu or Ile at position 8 and replacement of C-terminal hydrophobic amino acids with basic residues. AKAPCE·RCE complexes accumulate in intact cells.
Footnotes
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↵* This work was supported in part by National Institutes of Health Grant GM22792 (to C. S. R.) and a National Institutes of Health Pharmacological Sciences Training Grant GM07260 stipend (to R. A.).The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
The nucleotide sequence(s) reported in this paper has been submitted to the GenBank™/EMBL Data Bank with accession number(s) AF045926.
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↵‡ To whom correspondence should be addressed: Dept. of Molecular Pharmacology, F-229, Albert Einstein College of Medicine, 1300 Morris Park Ave., Bronx, New York 10461. Tel.: 718-430-2505; Fax: 718-430-8922; E-mail: rubin{at}aecom.yu.edu.
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↵1 The abbreviations used are: AKAP, A kinase anchor protein; R, regulatory subunits; C, catalytic subunit; PKA, protein kinase A; RII, regulatory subunits of type II PKA isoforms; RIα, regulatory subunit of type Iα PKA; RCE, regulatory subunit of C. elegans PKAI; GST, glutathioneS-transferase; PCR, polymerase chain reaction; IPTG, isopropyl-1-thio-β-d-galactopyranoside; kbp, kilobase pair; bp, base pair.
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↵2 R. Angelo and C. S. Rubin, unpublished results.
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↵3 In accordance with standard C. elegans nomenclature, genes are named with three lowercase letters and a number. kap is derived from kinaseanchor protein.
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- Received February 4, 1998.
- Revision received April 8, 1998.
- The American Society for Biochemistry and Molecular Biology, Inc.
