ABCMdb

PMID: 23223629

Jih KY, Hwang TC
Nonequilibrium gating of CFTR on an equilibrium theme.
Physiology (Bethesda). 2012 Dec;27(6):351-61. doi: 10.1152/physiol.00026.2012., [PubMed]

Sentences

No. Mutations Sentence Comment

87 ABCC7 p.Lys1250Ala ABCC7 p.Glu1371Ser Nonetheless, for hydrolysis-deficient mutants such as E1371S- and K1250A-CFTR, ATP is still capable of activating these channels and the open probability (Po) of these hydrolysis-deficient mutants is even higher than that of WT-CFTR, suggesting that, under an equilibrium condition when ATP hydrolysis is absent, CFTR can still function fairly well. Login to comment 155 ABCC7 p.Arg352Cys Fortuitously, this hydrolysis-dependent O1 &#a1; O2 transition was discerned in a CFTR mutant, R352C. Login to comment 156 ABCC7 p.Arg352Cys Single-channel recordings of R352C-CFTR revealed two distinguishable conductance states: a smaller one (O1), about one-third of the WT conductance, and a larger one (O2), about one-half of the WT conductance (8). Login to comment 161 ABCC7 p.Arg352Cys ABCC7 p.Glu1371Ser The idea that the C &#a1; O1 &#a1; O2 &#a1; C preferred transition is driven by ATP hydrolysis is supported not only by the time asymmetry but also by the observation that the O1 &#a1; O2 transition seen in an opening burst is abolished when the hydrolysis-deficient mutation (E1371S) is engineered into the R352C background. Login to comment 162 ABCC7 p.Arg352Cys An even more intriguing observation made with the R352C mutant channel is that, occasionally, there are opening events that consist of more than one O1 &#a1; O2 transition (boxed in FIGURE 3). Login to comment 170 ABCC7 p.Glu1371Ser Thus, in the absence of ATP hydrolysis, e.g., in E1371S-CFTR, the channel works simply because ATP-induced dimerization of NBDs promotes gate opening and the Po is exceedingly high because the channel is trapped in the stable O1 state. Login to comment 177 ABCC7 p.Arg352Cys ABCC7 p.Arg352Cys Unique gating features of R352C-CFTR Five representative traces from patches that contain only one R352C-CFTR in the presence of 2.75 mM ATP. Login to comment 178 ABCC7 p.Arg352Cys R352C-CFTR shows two distinct levels of open-state conductance: the smaller O1 and the larger O2. Login to comment 185 ABCC7 p.Met348Cys ABCC7 p.Ile344Cys Likewise in Bai et al. (8), chemical modifications of an engineered cysteine (I344C or M348C) in TM6 drastically increase ATP-independent activity to the level of ATP-dependent activity before modifications. Login to comment 191 ABCC7 p.Gly551Asp ABCC7 p.Gly551Asp This FDA-approved drug for CF treatment (1, 61) has been shown to increase the open time of both WTand G551D-CFTR (73, 83), a baffling result since, although WT channels are gated by ATP-induced NBD dimerization, the G551D mutation abolishes ATP responsiveness, presumably because introducing a negatively charged side chain at the signature sequence of NBD1 prevents NBD dimerization due to electrostatic repulsion (14). Login to comment 192 ABCC7 p.Gly551Asp Here, the new gating model offers a testable hypothesis that Kalydeco works by promoting spontaneous ATP-independent gating (C2 ࢒ O2 transitions), the part of the gating scheme likely preserved in G551D-CFTR. Login to comment 196 ABCC7 p.Arg352Cys The data on R352C-CFTR support the notion that a partial separation of the NBD dimer does not necessarily close the gate in the TMDs, but the fact that the O1 and O2 states exhibit different single-channel amplitudes indicates that ATP hydrolysis and/or subsequent partial separation of NBDs must affect the conformation of the ion permeation pathway in TMDs. Login to comment