ABCMdb

PMID: 11341822

Zou X, Hwang TC
ATP hydrolysis-coupled gating of CFTR chloride channels: structure and function.
Biochemistry. 2001 May 15;40(19):5579-86., 2001-05-15 [PubMed]

Sentences

No. Mutations Sentence Comment

56 ABCC7 p.Lys335Glu ABCC7 p.Lys95Asp For instance, replacing two positively charged residues with negatively charged residues in the M1 and M2 R-helices of MSD (K95D and K335E) alters the anion selectivity sequence of CFTR (17). Login to comment 57 ABCC7 p.Arg334Trp ABCC7 p.Arg347Pro Neutralizing a positively charged residue (R334W or R347P) diminishes the channel conductance (18). Login to comment 154 ABCC7 p.Lys1250Ala ABCC7 p.Lys1250Ala Converting lysine 1250 to alanine (K1250A) almost completely abolishes the ATPase activity (46). Login to comment 155 ABCC7 p.Lys1250Ala A critical role of this NBD2 lysine in CFTR gating was demonstrated by the result that the open time of the K1250A CFTR mutant is significantly prolonged from hundreds of milliseconds to minutes (38), an effect similar to the effect of AMP-PNP on wild-type channels (see the previous section). Login to comment 158 ABCC7 p.Lys464Ala ABCC7 p.Lys464Ala ABCC7 p.Lys464Ala Although earlier studies showed that converting lysine 464 to alanine (K464A) slowed opening (31, 32), a more recent report found that single-channel gating kinetics of the K464A mutant was almost indistinguishable from that of the wild-type CFTR (46-48). Login to comment 159 ABCC7 p.Lys464Ala The apparent affinity for ATP is little changed for the K464A channel (48). Login to comment 160 ABCC7 p.Lys464Ala Nevertheless, the ATP hydrolysis rate of the K464A mutant is decreased (46). Login to comment 165 ABCC7 p.Lys1250Ala Kinetic studies of the K1250A CFTR channels have refined the function of NBD2. Login to comment 166 ABCC7 p.Lys1250Ala It was first suggested that hydrolysis of ATP at NBD2 plays an obligatory role in closing of the channel since the K1250A mutant CFTR exhibits a much longer open time (31, 32). Login to comment 167 ABCC7 p.Lys1250Ala This model predicts that the open time of the K1250A mutant CFTR will be independent of the concentration of ATP. Login to comment 170 ABCC7 p.Lys1250Ala However, while the K1250A CFTR channel, once opened by a millimolar level of ATP, can remain open for minutes, the mean open time is only ~250 ms when the channel is opened by a low micromolar ATP concentration. Login to comment 172 ABCC7 p.Lys1250Ala Assuming that lowering the concentration of ATP only affects the probability of the occupancy of NBDs, Zeltwanger et al. (38) hypothesize that at low micromolar ATP concentrations, the K1250A CFTR channels close before ATP binds at NBD2. Login to comment 186 ABCC7 p.Asp1370Asn Gunderson and Kopito (31) demonstrated that the mean open time for the D1370N mutant is longer than that of the wild-type CFTR. Login to comment 187 ABCC7 p.Asp572Asn In a preliminary report, Vergani et al. (47) showed that the opening rate of the D572N mutant is reduced. Login to comment 194 ABCC7 p.Gln1291His ABCC7 p.Gln493Arg ABCC7 p.Gln1291Arg Interestingly, even relatively conserved mutations of these two glutamine residues (e.g., Q493R in NBD1 and Q1291R or Q1291H in NBD2) in the CFTR cause CF (Figure 3). Login to comment 200 ABCC7 p.Gly551Asp ABCC7 p.Gly551Asp Among them, the glycine-to-aspartate mutation (G551D) has a worldwide frequency of ~2%. Login to comment 201 ABCC7 p.Gly551Asp It has been shown that the G551D CFTR has a diminished ATPase activity, and the open probability of this mutant CFTR is less than 10% of that of wild-type channels (11). Login to comment 202 ABCC7 p.Gly551Asp By comparing ATP hydrolysis rates and gating parameters of wild-type and G551D CFTR channels, Bear et al. (50) were able to confirm the proposal that ATP hydrolysis is directly coupled to the individual gating transition (30, 38, 51; cf. ref 46). Login to comment 207 ABCC7 p.Ser1251Asn ABCC7 p.Ser466Leu ABCC7 p.Thr1252Pro ABCC7 p.Thr1246Ile Mutations of some of the corresponding amino acids in CFTR (S466L in NBD1 or T1246I, S1251N, and T1252P in NBD2) are associated with CF (Figure 3). Login to comment 236 ABCC7 p.Lys1250Ala ABCC7 p.Lys464Ala Their model is based mainly on the studies of the K464A and K1250A mutants, assuming mutations of the Walker A lysines diminish the level of ATP hydrolysis at respective NBDs. Login to comment 240 ABCC7 p.Lys1250Ala ABCC7 p.Lys464Ala This model explains the results showing that the K464A mutant shows a longer open time at micromolar ATP concentrations than that at millimolar ATP concentrations, whereas the K1250A mutant shows an opposite pattern of gating in response to changes in the ATP concentration (cf. ref 38). Login to comment 242 ABCC7 p.Lys464Ala For example, on the basis of the assumption of two open states in the NBD1 cycle, it is desirable to observe two distinct populations of open time for the K464A mutant especially at millimolar ATP concentrations. Login to comment 245 ABCC7 p.Lys1250Ala The demonstration that the K1250A mutant CFTR shows a drastically reduced ATP hydrolysis rate (48) is consistent with this idea of tight coupling since the duration of the gating cycle of this mutant is in the range of minutes (38). Login to comment 248 ABCC7 p.Lys464Ala To explain this result for the K464A mutant, one needs to speculate that hydrolysis of one ATP molecule may trigger several open-close events. Login to comment