A subset of GAF domains are evolutionarily conserved sodium sensors.
Most organisms maintain a transmembrane sodium gradient for cell function. Despite the importance of Na(+) in physiology, no directly Na(+)-responsive signalling molecules are known. The CyaB1 and CyaB2 adenylyl cyclases of the cyanobacterium Anabaena PCC 7120 are inhibited by Na(+). A D360A mutation in the GAF-B domain of CyaB1 ablated cAMP-mediated autoregulation and Na(+) inhibition. Na(+) bound the isolated GAF domains of CyaB2. cAMP blocked Na(+) binding to GAF domains but Na(+) had no effect on cAMP binding. Na(+) altered GAF domain structure indicating a mechanism of inhibition independent of cAMP binding. DeltacyaB1 and DeltacyaB2 mutant strains did not grow below 0.6 mM Na(+) and DeltacyaB1 cells possessed defects in Na(+)/H(+) antiporter function. Replacement of the CyaB1 GAF domains with those of rat phosphodiesterase type 2 revealed that Na(+) inhibition has been conserved since the eukaryotic/bacterial divergence. CyaB1 and CyaB2 are the first identified directly Na(+)-responsive signalling molecules that function in sodium homeostasis and we propose a subset of GAF domains underpin an evolutionarily conserved Na(+) signalling mechanism.
Cann
Martin
M
School of Biological and Biomedical Sciences, Durham University, South Road, Durham, UK. m.j.cann@durham.ac.uk
D000262:Adenylyl Cyclases / Q000378:metabolism; D000595:Amino Acid Sequence; D017033:Anabaena / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D000818:Animals; D001426:Bacterial Proteins / Q000037:antagonists & inhibitors / Q000737:chemistry* / Q000378:metabolism*; D020134:Catalytic Domain / Q000187:drug effects; D002942:Circular Dichroism; D017124:Conserved Sequence; D000242:Cyclic AMP / Q000378:metabolism; D054678:Cyclic Nucleotide Phosphodiesterases, Type 2; D004305:Dose-Response Relationship, Drug; D019143:Evolution, Molecular; D020035:Holoenzymes / Q000378:metabolism; D006706:Homeostasis / Q000187:drug effects; D008322:Mammals; D008954:Models, Biological; D010727:Phosphoric Diester Hydrolases / Q000378:metabolism; D017434:Protein Structure, Tertiary / Q000187:drug effects; D051381:Rats; D012964:Sodium / Q000378:metabolism* / Q000494:pharmacology
D001426:Bacterial Proteins; D020035:Holoenzymes; D012964:Sodium; D000242:Cyclic AMP; D010727:Phosphoric Diester Hydrolases; D054678:Cyclic Nucleotide Phosphodiesterases, Type 2; C517278:Pde2a protein, rat; D000262:Adenylyl Cyclases