ABCMdb

PMID: 9922376

Dawson DC, Smith SS, Mansoura MK
CFTR: mechanism of anion conduction.
Physiol Rev. 1999 Jan;79(1 Suppl):S47-75., [PubMed]

Sentences

No. Mutations Sentence Comment

248 ABCC7 p.Gly314Glu This effect is, in fact, seen in CFTR mutations (Fig. 3) is a function of the well depth, Gw 0 Gb , i.e. like G314E, which destabilizes relative anion binding, but also reduces single-channel conductance rather than increasing single-channel conductance as would be ex- bi Å expͫ0(Gw 0 Gb) RT ͬ (31) pected if only the well depth were affected (Mansoura and Dawson, unpublished data). Login to comment 337 ABCC7 p.Arg347Asp Block by DNDS was nearly makes them potentially very useful probes of the pore abolished in the R347D CFTR construct, whereas that by interior. The CFTR, and anion channels in general, tend DIDS was reduced but still readily apparent. Login to comment 350 ABCC7 p.Arg347Asp Sucrose when R347 in TM6 was substituted with aspartic acid (R347D). Login to comment 357 ABCC7 p.Arg347His ABCC7 p.Arg347Asp R347D construct, and if a histidine was substituted for R347 (R347H), the blocking effect of SCN (XSCN Å 0.075)The magnitude of the voltage dependence was consistent with the ion experiencing from 30 to 60% of the transmem- was greatly enhanced at pH 5.5, suggesting that the presence of the positive charge is important for the high-affin-brane potential as it accessed the binding site. Login to comment 359 ABCC7 p.Arg347Asp The single-channel conductance of R347D was reduced to Ç50% of wild-type CFTR and washanced when [Cl]o was reduced as expected if the two ions compete for a site in the pore. Login to comment 361 ABCC7 p.Arg347Asp Linsdell et al. (95) used rate theory models to simulate the anomalous moleuncharged, intracellular osmolytes, sucrose, sorbitol, and fraction effect seen with SCN and its absence in R347D It is of interest in this regard that there is evidence for tight binding of SCN to another well-characterizedCFTR. Login to comment 425 ABCC7 p.Gly314Glu ABCC7 p.Gly314Gln Iodide permeation ing must be interpreted with caution for a number of reasons. First, it has been demonstrated (101) that the In any survey of the permeation of monatomic and polyatomic anions through CFTR, iodide stands out asCFTR mutations (e.g., G314Q or G314E) result in CFTR channels that exhibit markedly reduced anion binding, exhibiting some unique, or perhaps exaggerated, properties. Login to comment 431 ABCC7 p.Lys95Asp The substitutions examined were K95D 101) or 1.0-2.0 (59, 145, 146). Login to comment 432 ABCC7 p.Arg347Glu ABCC7 p.Lys335Glu ABCC7 p.Arg1030Glu This behavior is consistent with the notion that iodide can reside in the channel with-(TM1), K335E (TM6), R347E (TM6), and R1030E (TM10). Login to comment 434 ABCC7 p.Lys335Glu ABCC7 p.Lys95Asp Finkelstein and Cass (55) called attention to the factthe order of 1:10, but two of the substitutions (K95D and K335E) altered the sequence of relative anion permeabilit- that the electrical behavior of planar lipid membranes bathed by iodide-containing solutions may be strongly in-ies by increasing the ratio for iodide, PI/PCl . Login to comment 436 ABCC7 p.Lys335Glu In the two mutant channels, this ratio was increased to Ç1.4, such that the selectivity sequence was their results suggested that the formation of the polyiodides can be effectively eliminated in the presence of aI ú Br ú Cl ú F. These substitutions, particularly K335E, also increased the apparent conductance ratio. Login to comment 437 ABCC7 p.Arg347Glu The R347E reducing agent like thiosulfate ion. Login to comment 441 ABCC7 p.Lys335Glu ABCC7 p.Lys335Asp The PI/PCl ratio was 0.44 for wild-type CFTR and increased F. Cysteine Accessibilityto 1.10 in K335E CFTR and 0.65 in K335D CFTR. Login to comment 449 ABCC7 p.Lys335Glu The ratio PI/PCl was increased in K335E CFTR but commonly employed are metals like Hg, Cd, or Ag or derivatives of methane thiosulfonate (MTS) first intro-was nevertheless substantially less than that predicted by the general pattern (101). Login to comment 475 ABCC7 p.Lys95Cys ABCC7 p.Gly91Cys ABCC7 p.Gln98Cys In three TM1 mutants, G91C, K95C, Q98C, all of which fall on the same face of a predicted TM1 a- ter`` is close to the cytoplasmic end of the pore and that R352 may play a role in determining charge selectivity forhelix, the conductance was irreversibly altered by either MTSES0 or MTSEA0 . Login to comment 479 ABCC7 p.Ile331Cys The cationic reagent also the results in terms of pore structure relies on the assumption that the only water-accessible surface at which engi-produced inhibition in one construct (I331C) in which the anionic MTSES0 did not. Login to comment 480 ABCC7 p.Arg347Cys ABCC7 p.Arg352Cys ABCC7 p.Arg334Cys Three residues, R334C, R347C, neered cysteines can react with the charged MTS reagents in the pore interior. The potential flaw in this assumptionand R352C, were also inhibited by the larger cation MTSET0 . Login to comment 481 ABCC7 p.Ile344Cys One construct, I344C, exhibited an increase in was elegantly demonstrated by Horn and co-workers (163) who showed that cysteine residues engineered intoconductance when exposed to MTSEA0 . Login to comment 556 ABCC7 p.Arg347His The more dramatic an R347H construct suggested that a positive charge at this locus was important for high-affinity SCN binding. Login to comment 557 ABCC7 p.Arg347Glu ABCC7 p.Arg347Gln Ineffect of mutations on anion binding suggests that permeant anions can interact with the channel sufficiently confirmation of these results, Smith and Dawson (unpublished data) found that blockade of CFTR by externalstrongly to impede conduction rates but that the ''tight binding`` is dependent on some element of pore conforma- SCN was abolished in R347E and also in R347Q CFTR, confirming the importance of the positive charge at thistion that is not critical to promote the entry of anions into the pore. Login to comment 559 ABCC7 p.Arg347Asp In a subsequent study, Linsdell and Hanrahan (93) showed that block by DIDS and DNDS was attenuated inbinding on channel structure was underscored by the finding that the dose-dependent activation of TM5 and the R347D CFTR. Login to comment 560 ABCC7 p.Lys335Asp Tabcharani et al. (147) found that the anomalousTM6 mutants by IBMX in the presence of forskolin was moderately to severely impaired, as if TM 5 and 6 are also mole fraction effect of SCN was reduced but not eliminated in a K335D construct. Login to comment 562 ABCC7 p.Lys335Ala ABCC7 p.Lys335Asp firmed that SCN binding was reduced but not eliminated in K335D and E CFTR and showed that simply deleting D. Structural Elements That Are Important for the charge (K335A) was without effect. Login to comment 569 ABCC7 p.Ser341Ala Substituting an alanine for serine-341 in TM6 virtually abolished theis the polarity and charge of each residue. Login to comment 575 ABCC7 p.Ser341Ala The single-channel conductance of S341A was reduced to Ç1 pS, and the macro- that anion binding might be a generalized feature of bundles of a-helices containing arginines, although Dormanscopic i-V relation became slightly inwardly rectifying, suggesting to the authors that this polar amino acid may et al. (43), in their analysis of a model for ion permeation in the gramicidin channel, suggested that anion interac-be pore-lining and also constitute a binding site for DPC, via hydrogen bonding with the -OH group. Login to comment 576 ABCC7 p.Ser1141Ala An analogous tions with the peptide backbone of this model system might produce energy minima that would behave as bind-substitution in TM12 (S1141A) did not alter anion conduction or DPC block but, if residues surrounding S1141 were ing sites. Login to comment 577 ABCC7 p.Ser341Ala One speculation is that TM5 and TM6 are both part of the ''lining`` of the pore such that the chargedaltered so as to match those surrounding S341 and then combined with the S341A mutation, binding was restored, residues in TM6 and the exact conformation of TM5 are both strong determinants of the types of interaction thatas if the binding site had been ''moved to TM12.`` The authors predicted that residues in TM6 and TM12 lying a permeating anion may experience with the pore wall. Login to comment 581 ABCC7 p.Lys335Glu The K335E construct was identical to wild type with regard to apparent affinity for DPC but did important for the conformational changes that gate the pore.display slight inward rectification. Login to comment 582 ABCC7 p.Lys335Phe Substituting the phenylalanine (K335F) led to a modest decrease in DPC binding Transmembrane segment 1 has been the subject of several studies that have not produced consonant results.and did not alter the i-V relation. Login to comment 584 ABCC7 p.Lys95Asp This substitu- K95, to aspartic acid (K95D) increased PI/PCl (6). Login to comment 585 ABCC7 p.Pro99Leu A patient mutation, P99L, was associated with reduced single-chan-tion reduced the single-channel conductance by Ç30%. Login to comment 590 ABCC7 p.Gly91Arg ABCC7 p.Gly91Glu ABCC7 p.Gly91Ala In addi-lectivity (see sect. IV), and in view of the roles of arginines in anion binding in other proteins (see sect. VE2), it is tion, Mansoura et al. (101) found that neutral (G91A), acidic (G91E), and basic (G91R) substitutions in this TMtempting to suggest that this TM might actually line the pore as suggested by the voltage-dependent accessibility had no effect on SCN binding or the sensitivity of the constructs to activation by IBMX, although the shape ofof some TM6 residues to MTS reagents (see sect. VF). Login to comment 591 ABCC7 p.Gly91Arg Linsdell and Hanrahan (92, 93) suggested that the cyto- the i-V plot was altered for G91R. Login to comment 593 ABCC7 p.Arg117His Sheppard et al. (137) reported that R117H CFTR exhibitedbut also of larger pore-occluding molecules such as DPC, DIDS, and organic anions (see sect. V). Login to comment 597 ABCC7 p.Gly314Glu ABCC7 p.Gly314Gln Transmembrane segment 2 and TM6 sequences formed anion-selective channels in bilayers,the site of two patient mutations, and found that SCN block of CFTR was abolished in G314E and G314Q CFTR, whereas peptides based on TM1, TM3, TM4, and TM5 did not. Login to comment 598 ABCC7 p.Gly314Ala ABCC7 p.Gly314Asp Mixtures of the TM2 and TM6 peptides producedmoderately impaired in G314A CFTR, and unaffected in G314D CFTR. Login to comment