ABCMdb

PMID: 18391167

Chen TY, Hwang TC
CLC-0 and CFTR: chloride channels evolved from transporters.
Physiol Rev. 2008 Apr;88(2):351-87., [PubMed]

Sentences

No. Mutations Sentence Comment

410 ABCC7 p.Tyr512Ala However, the corresponding mutation of Y512A in CLC-0 is almost without functional consequence (4). Login to comment 638 ABCC7 p.Glu1371Ser In addition, even the hydrolysis-deficient mutant E1371S-CFTR seldom assumes a stable open state in the presence of AMP-PNP alone (Cho and Hwang, unpublished data). Login to comment 684 ABCC7 p.Lys1250Ala ABCC7 p.Glu1371Ser However, since CFTR mutants whose ATP hydrolysis is abolished (e.g., K1250A, E1371S) (251, 302), once opened by ATP, can remain open for minutes (34, 112, 323, 324, 350; cf. Refs. 42, 251), it is now generally accepted that hydrolysis of ATP at ABP2 closes the channel (97, 358). Login to comment 715 ABCC7 p.Lys1250Ala For hydrolysis-deficient mutants such as K1250A, the bursting time estimated with different methods in different reports can differ by ϳ100-fold. Login to comment 718 ABCC7 p.Lys1250Ala (237) reported a locked open-time constant of ϳ2-3 min for K1250A-CFTR. Login to comment 732 ABCC7 p.Lys464Ala They showed that purified K464A-CFTR exhibits a nearly identical opening rate as wild-type channels at 1 mM ATP. Login to comment 734 ABCC7 p.Lys464Ala (237) not only confirmed this result, but also showed that the relationship between [ATP] and the opening rate is not affected by the K464A mutation, thus casting serious doubt on the role of ATP binding at ABP1 in channel opening. Login to comment 769 ABCC7 p.Glu1371Ser Since the spontaneous openings for the hydrolysis-deficient mutant E1371S are short-lived events (Cho and Hwang, unpublished observations), a stable NBD dimer formation requires the action of ATP presumably at ABP2. Login to comment 777 ABCC7 p.Lys1250Ala For example, the hydrolysis-deficient mutant K1250A-CFTR, once opened by ATP, stays open for minutes (but cf. Refs. 42, 251). Login to comment 785 ABCC7 p.Tyr1219Gly When Y1219 is mutated to a glycine (Y1219G), the ATP dose-response relationship shows a dramatic rightward shift with a K0.5 Ͼ50-fold higher than that of wild-type channels. Login to comment 786 ABCC7 p.Tyr1219Trp A more conservative mutation (Y1219W), however, did not change the K0.5 value significantly. Login to comment 787 ABCC7 p.Tyr1219Gly ABCC7 p.Tyr1219Ile ABCC7 p.Tyr1219Phe The ATP dose-response relationships of Y1219F and Y1219I mutants lie between those of wild type and Y1219G, suggesting a correlation between changes of the ATP sensitivity and the chemical natures of the side chain at this position. Login to comment 788 ABCC7 p.Tyr1219Gly ABCC7 p.Tyr1219Ile Single-channel kinetic analysis indicates that the shifts of the ATP dose-response relationships in Y1219G and Y1219I mutants are mainly due to changes of the opening rate (360). Login to comment 790 ABCC7 p.Tyr1219Gly Unlike the mutation at the Walker A lysine residue, the Y1219G mutation does not affect the open-time constant significantly, suggesting that the mutation does not alter ATP hydrolysis at ABP2. Login to comment 793 ABCC7 p.Trp401Gly ABCC7 p.Tyr1219Gly In addition, whether ATP binding at ABP1 is essential for channel opening by ATP binding at ABP2 is questioned since, unlike the Y1219G mutation, the W401G mutation in the ABP1 has little effect on the apparent affinity for ATP in both macroscopic and microscopic measurements (360). Login to comment 794 ABCC7 p.Lys464Ala ABCC7 p.Trp401Gly Although the mutations that presumably decrease ATP affinity at the ABP1 (K464A and W401G) have questionable effects on the ability of ATP to increase the opening rate of CFTR, both mutants show a shortened open time, suggesting a destabilization of the open state by the mutations (237, 360). Login to comment 795 ABCC7 p.Lys464Ala The effect of K464A on the open time was seen even in early studies (42, 251). Login to comment 796 ABCC7 p.Lys464Ala The shortened opening bursts of K464A-CFTR, compared with wild-type channels, are visually discernable in Ramjeesingh et al. Login to comment 800 ABCC7 p.Lys464Ala (324) reported that the open time for K464A-CFTR is not significantly different from that of wild-type channels. Login to comment 802 ABCC7 p.Lys464Ala It is, however, important to note that the K464A mutation does shorten the locked open time of hydrolysis-deficient mutants in two different studies (237, 324), suggesting that this effect on the open time is not due to a potential allosteric action of the mutations at the ABP1 on the ATP hydrolysis rate at the ABP2, which normally determines the rate of channel closing. Login to comment 804 ABCC7 p.Lys464Ala ABCC7 p.Trp401Gly Thus a reduction of the free energy of ATP binding could be reported as a decreased open-time constant as seen with the K464A and W401G mutants. Login to comment 810 ABCC7 p.Glu1371Ser P-ATP also increases the locked open time of the hydrolysis-deficient mutant E1371S-CFTR, suggesting that this effect of P-ATP is through a tighter binding. Login to comment 820 ABCC7 p.Glu1371Ser (360) examined the effect of mutations and a combination of mutations at W401, F409, and F430 residues on the open state (or NBD dimer) stability under the E1371S background. Login to comment 821 ABCC7 p.Glu1371Ser The locked open time of E1371S-CFTR was shortened in a graded manner as the number of altered aromatic amino acids was increased. Login to comment 824 ABCC7 p.Glu1371Ser (360) were able to show that P-ATP binds to ABP1 to prolong the open time of E1371S-CFTR. Login to comment 846 ABCC7 p.Gly551Asp ABCC7 p.Gly1349Asp Most notable are G551D and G1349D, two mutations located in the signature sequence of NBD1 (ABP2) and NBD2 (ABP1), respectively. Login to comment 847 ABCC7 p.Gly551Asp G551D is the third overall most common CF mutation, with a worldwide frequency of ϳ3% (www.genet.sickkids.on.ca/ cftr). Login to comment 849 ABCC7 p.Gly551Asp The G551D mutation results in a significantly decreased chloride current due to a drastic reduction of the channel activity (41, 73, 334, 337). Login to comment 850 ABCC7 p.Gly1349Asp On the contrary, the G1349D mutation causes a mild form of CF (271). Login to comment 853 ABCC7 p.Gly551Asp ABCC7 p.Gly1349Asp (35) indicate that the G551D mutation completely abolishes ATP-dependent gating of CFTR (also see Ref. 329), whereas G1349D-CFTR retains some ATP dependence albeit with a Po ϳ10-fold lower than that of WT-CFTR. Login to comment 866 ABCC7 p.Gly551Asp It is interesting to note that, although the activity of G551D-CFTR is ATP independent, 2Ј-deoxy-ATP increases the Po of this mutant mainly by prolonging the open time (41). Login to comment