ABCMdb

PMID: 9922377

Gadsby DC, Nairn AC
Control of CFTR channel gating by phosphorylation and nucleotide hydrolysis.
Physiol Rev. 1999 Jan;79(1 Suppl):S77-S107., [PubMed]

Sentences

No. Mutations Sentence Comment

47 ABCC7 p.Arg347His These biochemical resultsthe charge-neutralizing mutation R347H rendered single-channel conductance switchable between wild-type and provide a satisfying corollary to a substantial body of functional data that has established that opening and closingmutant values simply by changing cytoplasmic pH back and forth between 5.5 and 8.7 (195). Login to comment 50 ABCC7 p.Ser341Ala The mutation S341A, for instance, altered the apparent affinity (and its voltage dependence) for block tions IV and V, the details of this complex interplay between phosphorylation of CFTR, ATP hydrolysis atof open CFTR channels by diphenylamine-2-carboxylate (133), and a cysteine-scanning method has demonstrated CFTR`s NBDs, and CFTR channel gating remain incompletely understood. Login to comment 133 ABCC7 p.Ser660Ala ABCC7 p.Ser660Ala Along the same lines, coimmunoprecipitation experiments suggested that phosphorylation of functional decrements attending incorporation of addi- P33-8/ 9j0e$$ja10 01-13-99 16:19:50 prsa APS-Phys Rev tional mutations at Ser-422 to yield a 10SA mutant (31), single-channel currents in mutant CFTR missing R-domain residues 708-835 (CFTRDR), with (163) or withoutat Ser-753 to give the 11SA mutant (178), and at four remaining R-domain serines and threonines (S670, T690, (122, but cf. Ref. 164) additional mutation of Ser-660 to alanine (CFTRDR-S660A), does not constitute proof thatT787, and S790) mutated together to yield a (11/4)SA mutant (177). Login to comment 149 ABCC7 p.Ser422Ala On the other hand, the clear-cut decrement in channel function seen to be of major (e.g., Ser-660, -700, -737, -795, and -813) or minor (e.g., Ser-422 and -753) importance, coupled withupon adding the S422A mutation to the 9SA mutant (31) implies that Ser-422 does get phosphorylated in whole the apparent progressive decline of channel activity as the number of Ser-Ala mutations was increased, led toCFTR (at least, in 9SA mutant CFTR). Login to comment 175 ABCC7 p.Ser768Ala In vitro, pre- Po of S768A CFTR channels in excised patches exposed phosphorylation of CFTR by PKC did seem to enhance directly to PKA catalytic subunit suggest that phosphory- subsequent phosphorylation by PKA (31, but see discus- lation of Ser-768 somehow impedes phosphorylation of sion in Ref. 99). Login to comment 183 ABCC7 p.Ser813Ala ABCC7 p.Ser768Ala Nevertheless,site Ser-813 seems to be effectively canceled by phosphorylation of the major inhibitory site Ser-768, since the dou- PKC stimulation or application has invariably been found to potentiate subsequent CFTR channel activation byble mutant S768A/S813A had a K0.5 for IBMX comparable to that of wild-type CFTR channels (220). Login to comment 202 ABCC7 p.Ser686Ala although not examined at the single-channel level, the sensitivity of mutant S686A CFTR channels in oocytes to 4. Login to comment 358 ABCC7 p.Gly551Asp ABCC7 p.Gly551Asp Cystic fibrosis transmembrane conductance regulator also binds In the same study, the CF-associated CFTR mutant G551D was shown to hydrolyze ATP at only one-tenth the rateto PDZ2 of EBP50, but with much lower affinity, raising the possibility that PDZ-motif proteins other than CFTR of wild-type CFTR and, correspondingly, G551D channels opened only infrequently. Login to comment 386 ABCC7 p.Ser813Ala A qualitatively similar slowing of the activation of macroscopic CFTR conductance, relative totural and functional considerations have led to the suggestion that the NBDs of ABC transporters might more closely wild-type CFTR, was observed for mutant S813A channels expressed in oocytes, but because those activation ratesresemble the catalytic sites of GTPases than of ion-motive ATPases (27, 68, 124). Login to comment 465 ABCC7 p.Gln552His Functional analyses of CFTR channels bearing point mutations these results from G proteins, introduction of the mutation Q552H into NBD1 of CFTR slowed CFTR channelin these three key regions have begun to clarify the roles of the two NBDs in channel gating. Login to comment 466 ABCC7 p.His1350Gln opening without affecting closing, whereas making the converse mutation, H1350Q, in NBD2 accelerated channel closing without influencing the channel opening rate (27).2. Login to comment 471 ABCC7 p.Lys1250Met Although this would seem to rulestill able to open CFTR channels with a mutation, K1250M, in the NBD2 Walker A motif that was expected to impair out the postulated close structural relationship between G proteins and CFTR`s NBDs, the assignment of their rolesATP hydrolysis there (3). Login to comment 473 ABCC7 p.Gly551Asp Indeed, channel opening rate and ATPasefunction were found to favor the channel closed state when introduced in NBD1 but to favor the channel open rate are both markedly reduced in purified, reconstituted, mutant CFTR bearing the mutation G551D in the samestate when introduced into NBD2 (218, 219). Login to comment 558 ABCC7 p.Lys464Ala First,be sequential, although the precise nature and mechanism of the ordering remain to be determined. In keeping with they noted that the opening rate of mutant K464A CFTR channels was only approximately twofold lower than thatthe proposed role of PKA-mediated phosphorylation, presumably largely within the R domain, in modulating the of wild-type CFTR, whereas the equivalent mutation in other nucleoside triphosphatases (NTPases) reduces thefunction of NBD2, it has recently been shown that neither AMP-PNP nor PPi (both of which are believed to bind hydrolysis rate by several orders of magnitude. Login to comment 560 ABCC7 p.Lys464Ala Recent analyses of the dependence on temperature K464A in purified CFTR slows ATP hydrolysis only less than twofold (159). Login to comment 563 ABCC7 p.Gly1249Glu ABCC7 p.Gly1247Asp Second, mutant G1247D/G1249E CFTRphorylation status) of the closings are expected to be rate limited by ATP hydrolysis. Login to comment 567 ABCC7 p.Lys1250Ala K1250A CFTR channels bearing a mutation at the the functional analogy between CFTR`s NBDs and G proteins (discussed in sect. IVD2) could be resurrected andWalker A Lys of NBD2, expected to impair ATP hydrolysis there, have been reported to display slowed opening as reconciled with the new structural evidence. Login to comment 569 ABCC7 p.Lys1250Ala The overall result the information presently available, so they must await new experimental reults.is that Po of K1250A CFTR is reduced to about one-half that of wild-type CFTR channels (25, 159) and that the ATPase rate is even more markedly diminished (159). Login to comment 570 ABCC7 p.Lys1250Ala Sub- VI. CONCLUDING REMARKSstantially reduced ATPase activity of K1250A CFTR would be expected from the loss of ATP hydrolysis associated with wild-type CFTR channel closing, a loss inferred from The correlation between genotype and phenotype in terms of CF disease remains perplexingly elusive. Login to comment 571 ABCC7 p.Lys1250Ala But,detailed electrophysiological analysis of single K1250A channel records (75). Login to comment 572 ABCC7 p.Lys1250Ala If K1250A channels eventually close although in two-thirds of CF patients the disease stems from the same mutation in one chromosome 7 copy (caus-following dissociation, rather than hydrolysis, of the ATP at NBD2, the latter might reasonably be expected to tem- ing deletion of Phe-508), other influences of nature and nurture probably make it unrealistic to expect the sameporarily adopt a conformation different from that attained after hydrolysis. Login to comment