ABCMdb

PMID: 10398691

Csanady L, Gadsby DC
CFTR channel gating: incremental progress in irreversible steps.
J Gen Physiol. 1999 Jul;114(1):49-53., [PubMed]

Sentences

No. Mutations Sentence Comment

13 ABCC7 p.Lys1250Ala ABCC7 p.Lys464Ala The CFTR mutants K464A and K1250A, for instance, lie at the heart of challenges to the simple answers to both key questions. Login to comment 14 ABCC7 p.Lys1250Ala Thus, K1250A channels not only close much more slowly than wild-type (WT) channels, they also open more slowly, drawing speculation that ATP binding at NBD2 (rather than hydrolysis at NBD1) might trigger channel opening (Gunderson and Kopito, 1995; compare Sheppard and Welsh, 1999). Login to comment 15 ABCC7 p.Lys1250Ala ABCC7 p.Lys1250Ala ABCC7 p.Lys464Ala ABCC7 p.Lys464Ala And recent direct measurements on purified, reconstituted CFTR have revealed virtual abolition of ATPase activity by K1250A, a more than sevenfold reduction of ATP hydrolysis (compared with WT) for K464A, but only an approximately twofold decrement in open probability (Po) for K1250A channels (because the effect of their markedly slower closing is more than offset by that of their slowed opening) and an even smaller drop in Po (due to slightly slower opening) for K464A relative to WT (Ramjeesingh et al., 1999), prompting the conclusion that ATP hydrolysis and channel gating are not tightly coupled. Login to comment 16 ABCC7 p.Lys1250Ala As pointed out by Zeltwanger et al. (1999) (compare Gadsby and Nairn, 1999), it is not difficult to explain the K1250A findings, since the very low ATPase activity correlates well with observations of very few openings (still conceivably associated with ATP hydrolysis at NBD1) and, after very long open times, an equal number of closings that are presumably associated with dissociation of the ATP, not its hydrolysis, at NBD2. Login to comment 17 ABCC7 p.Lys464Ala ABCC7 p.Lys464Ala Although it is harder to reconcile the substantially reduced ATPase activity of K464A with its barely altered gating (Ramjeesingh et al., 1999), others have noted that K464A CFTR channels open two- (Gunderson and Kopito, 1995) or fivefold (Carson et al., 1995) more slowly than WT. Login to comment 44 ABCC7 p.Lys1250Ala Zeltwanger et al. (1999) examined K1250A CFTR channels and found, at millimolar ATP, the extremely long open times (mean ~3 min) reported by others, but, at 10 ␮M ATP, only the same brief openings (mean ~250 ms) observed for WT CFTR at low [ATP]. Login to comment 46 ABCC7 p.Lys1250Ala In other words, the brief openings of both WT and K1250A CFTR channels are interpreted as simply reflecting ATP binding and hydrolysis, and dissociation of the hydrolysis products, at NBD1. Login to comment