Paper
2,3-Butanedione Monoxime Affects Cystic Fibrosis Transmembrane Conductance Regulator Channel Function through Phosphorylation-Dependent and Phosphorylation-Independent Mechanisms: The Role of Bilayer Material Properties
Published Dec 1, 2006 · P. Artigas, S. Al’Aref, E. A. Hobart
Molecular Pharmacology
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Abstract
2,3-Butanedione monoxime (BDM) is widely believed to act as a chemical phosphatase. We therefore examined the effects of BDM on the cystic fibrosis transmembrane regulator (CFTR) Cl- channel, which is regulated by phosphorylation in a complex manner. In guinea pig ventricular myocytes, forskolin-activated whole-cell CFTR currents responded biphasically to external 20 mM BDM: a rapid ∼2-fold current activation was followed by a slower (τ ∼20 s) inhibition (to ∼20% of control). The inhibitory response was abolished by intracellular dialysis with the phosphatase inhibitor microcystin, suggesting involvement of endogenous phosphatases. The BDM-induced activation was studied further in Xenopus laevis oocytes expressing human epithelial CFTR. The concentration for half-maximal BDM activation (K0.5) was state-dependent, ∼2 mM for highly and ∼20 mM for partially phosphorylated channels, suggesting a modulated receptor mechanism. Because BDM modulates many different membrane proteins with similar K0.5 values, we tested whether BDM could alter protein function by altering lipid bilayer properties rather than by direct BDM-protein interactions. Using gramicidin channels of different lengths (different channel-bilayer hydrophobic mismatch) as reporters of bilayer stiffness, we found that BDM increases channel appearance rates and lifetimes (reduces bilayer stiffness). At 20 mM BDM, the appearance rates increase ∼4-fold (for the longer, 15 residues/monomer, channels) to ∼10-fold (for the shorter, 13 residues/monomer channels); the lifetimes increase ∼50% independently of channel length. BDM thus reduces the energetic cost of bilayer deformation, an effect that may underlie the effects of BDM on CFTR and other membrane proteins; the state-dependent changes in K0.5 are consistent with such a bilayer-mediated mechanism.
2,3-Butanedione monoxime (BDM) increases CFTR channel appearance rates and lifetimes by reducing bilayer stiffness, potentially impacting protein function through phosphorylation-dependent and -independent mechanisms.
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