Role of CBS and Bateman Domains in Phosphorylation-Dependent Regulation of a CLC Anion Channel.
Eukaryotic CLC anion channels and transporters are homodimeric proteins composed of multiple α-helical membrane domains and large cytoplasmic C-termini containing two cystathionine-β-synthase domains (CBS1 and CBS2) that dimerize to form a Bateman domain. The Bateman domains of adjacent CLC subunits interact to form a Bateman domain dimer. The functions of CLC CBS and Bateman domains are poorly understood. We utilized the Caenorhabditis elegans CLC-1/2/Ka/Kb anion channel homolog CLH-3b to characterize the regulatory roles of CLC cytoplasmic domains. CLH-3b activity is reduced by phosphorylation or deletion of a 14-amino-acid activation domain (AD) located on the linker connecting CBS1 and CBS2. We demonstrate here that phosphorylation-dependent reductions in channel activity require an intact Bateman domain dimer and concomitant phosphorylation or deletion of both ADs. Regulation of a CLH-3b AD deletion mutant is reconstituted by intracellular perfusion with recombinant 14-amino-acid AD peptides. The sulfhydryl reactive reagent 2-(trimethylammonium)ethyl methanethiosulfonate bromide (MTSET) alters in a phosphorylation-dependent manner the activity of channels containing single cysteine residues that are engineered into the short intracellular loop connecting membrane α-helices H and I (H-I loop), the AD, CBS1, and CBS2. In contrast, MTSET has no effect on channels in which cysteine residues are engineered into intracellular regions that are dispensable for regulation. These studies together with our previous work suggest that binding and unbinding of the AD to the Bateman domain dimer induces conformational changes that are transduced to channel membrane domains via the H-I loop. Our findings provide new, to our knowledge, insights into the roles of CLC Bateman domains and the structure-function relationships that govern the regulation of CLC protein activity by diverse ligands and signaling pathways.
MDI Biological Laboratory, Kathryn W. Davis Center for Regenerative Biology and Medicine, Salisbury Cove, Maine.
Toshiki
T
Yamada
Department of Molecular Structure and Function, Hospital for Sick Kids, Toronto, Ontario.
Mickael
M
Krzeminski
Department of Molecular Structure and Function, Hospital for Sick Kids, Toronto, Ontario.
Zoltan
Z
Bozoky
Department of Molecular Structure and Function, Hospital for Sick Kids, Toronto, Ontario.
Julie D
JD
Forman-Kay
MDI Biological Laboratory, Kathryn W. Davis Center for Regenerative Biology and Medicine, Salisbury Cove, Maine. Electronic address: kstrange@mdibl.org.
Kevin
K
Strange
D000595:Amino Acid Sequence; D000818:Animals; D017173:Caenorhabditis elegans / Q000166:cytology / Q000378:metabolism; D029742:Caenorhabditis elegans Proteins / Q000737:chemistry* / Q000378:metabolism*; D018118:Chloride Channels / Q000737:chemistry* / Q000378:metabolism*; D003541:Cystathionine beta-Synthase / Q000737:chemistry*; D057809:HEK293 Cells; D006801:Humans; D015640:Ion Channel Gating; D008024:Ligands; D008958:Models, Molecular; D010766:Phosphorylation; D000072417:Protein Domains; D015398:Signal Transduction
C086321:CLC-1 channel; D029742:Caenorhabditis elegans Proteins; D018118:Chloride Channels; D008024:Ligands; D003541:Cystathionine beta-Synthase