ADP Inhibits Function of the ABC Transporter Cystic Fibrosis Transmembrane Conductance Regulator via Its Adenylate Kinase Activity

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 102; no. 6; pp. 2216 - 2220
• Main Authors: Randak, Christoph O., Welsh, Michael J.
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences 08-02-2005; National Acad Sciences
• Subjects: ABC transporters; Adenosine Diphosphate - metabolism; Adenosine triphosphatases; Adenylate Kinase - antagonists & inhibitors; Adenylate Kinase - metabolism; ATP binding cassette transporters; Biological Sciences; Chlorides - metabolism; Cystic fibrosis; Cystic Fibrosis Transmembrane Conductance Regulator - genetics; Cystic Fibrosis Transmembrane Conductance Regulator - metabolism; Diphosphates; Enzymes; Grants; HeLa Cells; Humans; Membranes; Molecules; Mutation; Nucleotides; Patch-Clamp Techniques; Phosphorylation; Physiological regulation; Protein Structure, Tertiary; Salts
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.0409787102

ADP interacts with the nucleotide-binding domains (NBDs) of the cystic fibrosis transmembrane conductance regulator (CFTR) to inhibit its Cl-channel activity. Because CFTR NBD2 has reversible adenylate kinase activity (ATP + AMP ⇆ ADP + ADP) that gates the channel, we asked whether ADP might inhibit current through this enzymatic activity. In adenylate kinases, binding of the two ADP molecules is cooperative. Consistent with this hypothesis, CFTR current inhibition showed positive cooperativity for ADP. We also found that ADP inhibition of current was attenuated when we prevented adenylate kinase activity with P1, P5- di(adenosine-5′) pentaphosphate. Additional studies suggested that adenylate kinase-dependent inhibition involved phosphotransfer between two nucleotide diphosphates. These data indicate that the adenylate kinase reaction at NBD2 contributed to the inhibitory effect of ADP. Finding that ADP inhibits function via an adenylate kinase activity also helps explain the earlier observation that mutations that disrupt adenylate kinase activity also disrupt ADP inhibition. Thus, the results reveal a previously unrecognized mechanism by which ADP inhibits an ABC transporter.