Single amino acids in the carboxyl terminal domain of aquaporin-1 contribute to cGMP-dependent ion channel activation.
BACKGROUND
Aquaporin-1 (AQP1) functions as an osmotic water channel and a gated cation channel. Activation of the AQP1 ion conductance by intracellular cGMP was hypothesized to involve the carboxyl (C-) terminus, based on amino acid sequence alignments with cyclic-nucleotide-gated channels and cGMP-selective phosphodiesterases.


RESULTS
Voltage clamp analyses of human AQP1 channels expressed in Xenopus oocytes demonstrated that the nitric oxide donor, sodium nitroprusside (SNP; 3-14 mM) activated the ionic conductance response in a dose-dependent manner. Block of soluble guanylate cyclase prevented the response. Enzyme immunoassays confirmed a linear dose-dependent relationship between SNP and the resulting intracellular cGMP levels (up to 1700 fmol cGMP /oocyte at 14 mM SNP). Results here are the first to show that the efficacy of ion channel activation is decreased by mutations of AQP1 at conserved residues in the C-terminal domain (aspartate D237 and lysine K243).


CONCLUSIONS
These data support the idea that the limited amino acid sequence similarities found between three diverse classes of cGMP-binding proteins are significant to the function of AQP1 as a cGMP-gated ion channel, and provide direct evidence for the involvement of the AQP1 C-terminal domain in cGMP-mediated ion channel activation.
Boassa
Daniela
D
Program in Neuroscience, University of Arizona, Tucson, Arizona 85724-5051, USA. dboassa@email.arizona.edu
Yool
Andrea J
AJ
D000595:Amino Acid Sequence / Q000502:physiology; D000596:Amino Acids / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D051398:Aquaporin 1; D020346:Aquaporins / Q000096:biosynthesis / Q000737:chemistry* / Q000235:genetics / Q000502:physiology*; D001789:Blood Group Antigens; D017124:Conserved Sequence / Q000502:physiology; D006152:Cyclic GMP / Q000096:biosynthesis / Q000502:physiology*; D054815:Cyclic Nucleotide-Gated Cation Channels; D004305:Dose-Response Relationship, Drug; D005260:Female; D006801:Humans; D007473:Ion Channels / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism / Q000502:physiology; D008564:Membrane Potentials / Q000187:drug effects / Q000235:genetics / Q000502:physiology; D016297:Mutagenesis, Site-Directed / Q000235:genetics / Q000502:physiology; D020030:Nitric Oxide Donors / Q000494:pharmacology; D009599:Nitroprusside / Q000494:pharmacology; D009865:Oocytes / Q000737:chemistry / Q000166:cytology / Q000378:metabolism; D009997:Osmotic Pressure; D018408:Patch-Clamp Techniques / Q000379:methods; D010455:Peptides / Q000502:physiology*; D017434:Protein Structure, Tertiary / Q000502:physiology; D014982:Xenopus laevis / Q000196:embryology / Q000235:genetics / Q000378:metabolism
C496020:AQP1 protein, human; D000596:Amino Acids; D020346:Aquaporins; D001789:Blood Group Antigens; D054815:Cyclic Nucleotide-Gated Cation Channels; D007473:Ion Channels; D020030:Nitric Oxide Donors; D010455:Peptides; D051398:Aquaporin 1; D009599:Nitroprusside; D006152:Cyclic GMP