Adenylate Kinase Activity Controls Cystic Fibrosis Channel Protein

A recent study suggests that the mechanism by which the cystic fibrosis transmembrane conductance regulator protein (CFTR) opens ion channels in lung cells is that of an adenylate kinase enzyme and not that of an ATPase as had been previously believed.

Adenylate kinase catalyzes the phosphorylation of adenosine 5'-phosphate (AMP) to adenosine 5'-disphosphate (ADP) in the presence of ATP or inorganic triphosphate in a reaction that neither requires nor releases energy. This type of reaction better fits the evidence indicating that while ATP is required for CFTR channel formation, energy such as that provided by ATPase breakdown of ATP is not required for ions to flow through the channel.

Investigators at the University of Iowa (Iowa City, USA) revealed in the December 26, 2003, issue of Cell that at physiologic nucleotide concentrations, adenylate kinase activity, rather than ATPase activity, may control gating (the process by which ion channels open and close their pores) and therefore involve little energy consumption.
CFTR is a member of the ABC transporter family, the largest group of proteins that move molecules across membranes. "ABC transporter proteins contain a very conserved ‘engine' that controls transport,” explained Dr. Chrisoph Randak, a postdoctoral investigator at the University of Iowa. "Our study indicates that at least in CFTR that ‘engine' can be run either by an ATPase, which uses energy, or an adenylate kinase, which is energy-neutral.”




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