title: Structural diversity of the cAMP-dependent protein kinase regulatory subunit in Caenorhabditis elegans.
abstract: The cAMP-dependent protein kinase (protein kinase A, PK-A) plays a key role in the control of eukaryotic cellular activity. The enzymology of PK-A in the free-living nematode, Caenorhabditis elegans is deceptively simple. Single genes encode the catalytic (C) subunit (kin-1), the regulatory (R) subunit (kin-2) and an A-kinase anchor protein (AKAP) (aka-1); nonetheless, PK-A is able to facilitate a comprehensive array of cAMP-mediated processes in this model multicellular organism. We have previously demonstrated that, in C. elegans, as many as 12 different isoforms of the C-subunit arise as a consequence of alternative splicing strategies. Here, we report the occurrence of transcripts encoding novel isoforms of the PK-A R-subunit in C. elegans. In place of exons 1 and 2, these transcripts include coding sequences from novel B or Q exons directly linked to exon 3, thereby generating isoforms with novel N-termini. R-subunits containing an exon B-encoded N-terminal polypeptide sequence were detected in extracts prepared from mixed populations of C. elegans. Of note is the observation that R-subunit isoforms containing exon B- or exon Q-encoded polypeptide sequences lack the dimerisation/docking domains conventionally seen in R-subunits. This means that they are unlikely to participate in the formation of tetrameric PK-A holoenzymes and, additionally, they are unlikely to interact with AKAP(s). It is therefore possible that, in C. elegans, in addition to tetrameric (R(2)C(2)) PK-A holoenzymes, there is also a sub-population of dimeric (RC) PK-A enzymes that are not tethered by AKAPs. Furthermore, inspection of the N-terminal sequence encoded by exon B suggests that this isoform is a likely target for N-myristoylation. Although unusual, a number of similarly N-myristoylatable R-subunits, from a range of different species, are present in the databases, suggesting that this may be a more generally observed feature of R-subunit structure. The occurrence of R-subunit isoforms, without dimerisation/docking domains (with or without N-myristoylatable N-termini) in other species would suggest that the control of PK-A activity may be more complex than hitherto thought.
authors.affiliation: Institute of Integrative Biology, University of Liverpool, Biosciences Building, Crown St., Liverpool, L69 7ZB, UK.
authors.forename: Martyna W
authors.initials: MW
authors.lastname: Pastok
authors.forename: Mark C
authors.initials: MC
authors.lastname: Prescott
authors.forename: Caroline
authors.initials: C
authors.lastname: Dart
authors.forename: Patricia
authors.initials: P
authors.lastname: Murray
authors.forename: Huw H
authors.initials: HH
authors.lastname: Rees
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Fisher
mesh_terms: D000818:Animals; D001483:Base Sequence; D017173:Caenorhabditis elegans / Q000201:enzymology*; D002851:Chromatography, High Pressure Liquid; D017868:Cyclic AMP-Dependent Protein Kinases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D005091:Exons; D013058:Mass Spectrometry; D008969:Molecular Sequence Data; D020033:Protein Isoforms / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D017434:Protein Structure, Tertiary; D021122:Protein Subunits / Q000737:chemistry / Q000235:genetics / Q000378:metabolism
chemical_list: D020033:Protein Isoforms; D021122:Protein Subunits; D017868:Cyclic AMP-Dependent Protein Kinases