A mutation in CFTR modifies the effects of the adenylate kinase inhibitor Ap5A on channel gating.
Mutations in the gene that encodes the cystic fibrosis transmembrane conductance regulator (CFTR) cause cystic fibrosis. The CFTR anion channel is controlled by ATP binding and enzymatic activity at the two nucleotide-binding domains. CFTR exhibits two types of enzymatic activity: 1), ATPase activity in the presence of ATP and 2), adenylate kinase activity in the presence of ATP plus physiologic concentrations of AMP or ADP. Previous work showed that P(1),P(5)-di(adenosine-5')pentaphosphate (Ap(5)A), a specific adenylate kinases inhibitor, inhibited wild-type CFTR. In this study, we report that Ap(5)A increased activity of CFTR with an L1254A mutation. This mutation increased the EC50 for ATP by >10-fold and reduced channel activity by prolonging the closed state. Ap(5)A did not elicit current on its own nor did it alter ATP EC50 or maximal current. However, it changed the relationship between ATP concentration and current. At submaximal ATP concentrations, Ap(5)A stimulated current by stabilizing the channel open state. Whereas previous work indicated that adenylate kinase activity regulated channel opening, our data suggest that Ap(5)A binding may also influence channel closing. These results also suggest that a better understanding of the adenylate kinase activity of CFTR may be of value in developing new therapeutic strategies for cystic fibrosis.
Dong
Qian
Q
Departments of Internal Medicine and Molecular Physiology and Biophysics, Howard Hughes Medical Institute, Roy J and Lucille A Carver College of Medicine, University of Iowa, Iowa City, Iowa 52242, USA.
Randak
Christoph O
CO
Welsh
Michael J
MJ
D015720:5'-Nucleotidase / Q000037:antagonists & inhibitors*; D000249:Adenosine Monophosphate / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism; D001665:Binding Sites; D019005:Cystic Fibrosis Transmembrane Conductance Regulator / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D003600:Cytosol; D015226:Dinucleoside Phosphates / Q000494:pharmacology*; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D006367:HeLa Cells; D006801:Humans; D015640:Ion Channel Gating / Q000187:drug effects*; D017354:Point Mutation; D055503:Protein Multimerization; D055550:Protein Stability; D020836:Protein Structure, Quaternary; D017434:Protein Structure, Tertiary
D015226:Dinucleoside Phosphates; D004791:Enzyme Inhibitors; D019005:Cystic Fibrosis Transmembrane Conductance Regulator; D000249:Adenosine Monophosphate; C012275:P(1),P(5)-di(adenosine-5'-)pentaphosphate; D000255:Adenosine Triphosphate; D015720:5'-Nucleotidase