Missfiring mechanism in NBD gating engine of CFTR chloride channel

Abstract

CFTR channel is a good model for studying mechanism of NBD gating engine which is common in ABC trasnporter superfamily because we can observe motion of the NBD engine as channel gating in a real time base using patch-clamp technique. There is convincing evidence that opening of the CFTR channel is associated with dimerization of CFTR's two NBDs (NBD1 and NBD2). Contrary to wild-type (WT) CFTR, which usually opens for hundreds of milliseconds, hydrolysis-deficient mutants can open for minutes. Interestingly, we observed that WT-CFTR occasionally shows long-lasting openings similar to that of hydrolysis-deficient mutants. We investigated the mechanism of the occasional long-opening events shown in WT-CFTR. WT-CFTR showed a fast single exponential relaxation in the macroscopic current relaxation after a rapid removal of ATP in excised inside-out patches. However, mutations in Y1219 which were supposed to interact with the adenine ring of ATP at NBD2, induced an additional significant slow phase in the current relaxation. The increases of fraction and time constant of the Y1219 mutation-induced slow phase were correlated with ATP dose-response curve shift shown in each Y1219 mutant, which suggested that less ATP binding affinity in NBD2 caused more long-opening of CFTR channel. We concluded that Y1219 residue mediated the stable binding of ATP molecule to NBD2 and the instability of ATP binding to NBD2 caused long-opening of CFTR channel presumably via a failure of ATP hydrolysis. [J Physiol Sci. 2008;58 Suppl:S84]