Cystic fibrosis transmembrane conductance regulator (CFTR) is definitely a membrane-spanning adenosine

Cystic fibrosis transmembrane conductance regulator (CFTR) is definitely a membrane-spanning adenosine 5′-triphosphate (ATP)-binding cassette (ABC) transporter. of adenosine 5′-monophosphate (AMP) CFTR Cl? channel function is coupled to adenylate kinase activity (ATP+AMP ? 2 ADP). Work with Rad50 and SMC showed that these enzymes catalyze both ATPase and Ataluren adenylate kinase reactions. However despite the supportive electrophysiological results with CFTR there are no biochemical data demonstrating intrinsic adenylate kinase activity of a membrane-bound ABC transporter. We developed a biochemical assay for adenylate kinase activity in which the radioactive γ-phosphate of a nucleotide triphosphate could transfer to a photoactivatable AMP analog. UV irradiation could then trap the 32P on the adenylate kinase. With Rabbit polyclonal to ARF3. this assay we discovered phosphoryl group transfer that labeled CFTR thereby demonstrating its adenylate kinase activity. Our results also suggested that the interaction of nucleotide triphosphate with CFTR at ATP-binding site 2 is required for adenylate kinase activity. These biochemical data complement earlier biophysical studies of Ataluren CFTR and indicate that the ABC transporter CFTR can function as an adenylate kinase. they can hydrolyze ATP to adenosine 5′-diphosphate (ADP) and inorganic phosphate (Pi) (ATP+H2O → ADP+Pi). The conformational Ataluren changes associated with ATP binding and hydrolysis are coupled to the biological function of the ABC protein (10-13); in CFTR this is opening and closing of the channel (14-17). Recent studies with CFTR (18 19 and two other ABC proteins the DNA repair enzyme Rad50 (20) and a structural maintenance of chromosome (SMC) protein (21) challenge the model that the function of all ABC proteins depends solely on their associated ATPase activity. CFTR opening and closing depends on ATPase activity if ATP is the only nucleotide present (14-17). However patch clamp studies using excised membrane patches containing CFTR indicated that in the presence of physiologically relevant concentrations of adenosine 5′-monophosphate (AMP) adenylate kinase activity is coupled to channel function (18). Adenylate kinases are enzymes that bind ATP and AMP at separate sites and catalyze the transfer of the γ-phosphoryl group of ATP onto the α-phosphate of AMP (ATP+AMP ? 2 ADP) (22). The ABC proteins Rad50 (20) and SMC (21) which are not transporters but nuclear proteins involved in DNA repair and chromosome maintenance have been shown to catalyze both ATPase and adenylate kinase reactions. Furthermore Bhaskara (20) showed that a yeast strain with a Rad50 mutation that reduced its adenylate kinase but not its ATPase activity resembled a Rad50 null strain with regard to meiosis and telomere maintenance. This result suggests an important physiologic role for Rad50 adenylate kinase activity. Lammens and Hopfner (21) solved the crystal structure of the ABC-NBD of the SMC protein in complex with the adenylate kinase inhibitor Ap5A providing the first structural view of the active center of an ABC adenylate kinase. Ap5A contains two adenosine groups connected by five phosphate Ataluren groups allowing it to bind simultaneously to an ATP- and an AMP-binding site (23). The structure showed the two adenosine moieties of Ap5A attached to two binding sites separated by ~15 ?. A Mg2+ ion one adenosine plus α- β- and γ-phosphates of Ap5A destined the canonical Mg2+-ATP-binding site on lobe I from the SMC NBD. The additional adenosine the “AMP” adenosine group stacked onto the medial side chain of the conserved glutamine from the Q-loop in the user interface of lobe I and lobe II. A recently available research assessed ATPase and adenylate kinase activity of recombinant CFTR after solubilizing it from membranes using 8% (v/v) pentadecafluorooctanoic acidity (24). The analysis didn’t detect adenylate kinase activity as well as the authors figured Ataluren CFTR can be an ATPase however not an adenylate kinase. That research raised queries of if a membrane-bound ABC transporter could work as an adenylate kinase. Furthermore the discrepancy between your electrophysiological research with membrane-embedded CFTR as well as the biochemical research with membrane-solubilized CFTR recommended the need for tests for adenylate kinase activity.

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