ABCMdb

PMID: 24727426

Wang Y, Wrennall JA, Cai Z, Li H, Sheppard DN
Understanding how cystic fibrosis mutations disrupt CFTR function: from single molecules to animal models.
Int J Biochem Cell Biol. 2014 Jul;52:47-57. doi: 10.1016/j.biocel.2014.04.001. Epub 2014 Apr 13., [PubMed]

Sentences

No. Mutations Sentence Comment

1865 ABCC7 p.Gly551Asp Only one drug that targets mutant CFTR (ivacaftor [KalydecoTM; VX-770]) is available to a small number of CF patients bearing the G551D mutation (Van Goor et al., 2009; Ramsey et al., 2011). Login to comment 1915 ABCC7 p.Arg352Cys However, Jih et al. (2012) interpreted the sojourns of the CFTR construct Cysless-R352C-CFTR to sub-conductance states to suggest that more than one ATP molecule might be hydrolysed during an open channel burst. Login to comment 1918 ABCC7 p.Gly551Asp It has also been used to provide an explanation for the impact of the CF mutation G551D on channel gating and the action of the CFTR potentiator ivacaftor (see Section 3.3). Login to comment 1947 ABCC7 p.Trp1282* ABCC7 p.Gly542* Common examples include G542X, the second most common CF mutation, prevalent in Mediterranean countries and W1282X, the most common CF mutation in Ashkenazi Jews. Login to comment 1973 ABCC7 p.Gly551Asp The best known class III mutation is G551D, the third commonest CF mutation, associated with a severe disease phenotype (Welsh et al., 2001) and first to be treated with a clinically approved CFTR potentiator (ivacaftor) (Van Goor et al., 2009; Ramsey et al., 2011). Login to comment 1975 ABCC7 p.Gly551Asp Unsurprisingly, therefore replacement of a hydrogen atom by a large acidic side chain in G551D has devastating consequences for CFTR channel gating (Li et al., 1996; Cai et al., 2006; Bompadre et al., 2007). Login to comment 1976 ABCC7 p.Gly551Asp Bompadre et al. (2007) argue that the molecular basis of the G551D mutation is not the prevention of ATP binding at site 2, but the obstruction of conformational changes subsequent to ATP binding that gate the channel pore. Login to comment 1977 ABCC7 p.Gly551Asp In support of this idea, the authors demonstrated that the gating behaviour of G551D represents the spontaneous ATP-independent activity of wild-type CFTR (Bompadre et al., 2007). Login to comment 1978 ABCC7 p.Gly551Asp Interestingly, ivacaftor enhances strongly ATP-independent channel gating by G551D-CFTR (Eckford et al., 2012; Jih and Hwang, 2013). Login to comment 1981 ABCC7 p.Gly551Asp ABCC7 p.Gly1349Asp Interestingly, the CF mutation G1349D is the mirror image of G551D in ATP-binding site 1. Login to comment 1982 ABCC7 p.Gly551Asp ABCC7 p.Gly1349Asp In contrast, to G551D, G1349D retains some ATP-dependence, albeit with an altered relationship between ATP concentration and channel activity (Bompadre et al., 2007). Login to comment 1983 ABCC7 p.Gly1349Asp The data suggest that G1349D disrupts CFTR function by hindering NBD dimerization (Bompadre et al., 2007). Login to comment 1984 ABCC7 p.Gly551Asp ABCC7 p.Gly1349Asp Our own studies demonstrate that with some differences G551D and G1349D disrupt severely channel gating by decreasing the duration of channel openings and prolonging greatly the long closures that separate channel openings (Fig. 4) (Cai et al., 2006). Login to comment 1985 ABCC7 p.Gly551Asp ABCC7 p.Gly1349Asp They also suggest that G551D-CFTR and G1349D-CFTR have distinct pharmacological profiles based on their responses to phloxine B, pyrophosphate and 2-deoxy-ATP, three agents that potentiate channel gating by different mechanisms (Cai et al., 2006). Login to comment 1986 ABCC7 p.Gly551Asp ABCC7 p.Gly1349Asp By contrast, Yu et al. (2012) demonstrated that ivacaftor potentiated robustly both G551D-CFTR and G1349D-CFTR with similar potency, but different efficacy. Login to comment 1987 ABCC7 p.Arg117His ABCC7 p.Arg668Cys ABCC7 p.Ala1067Thr Encouragingly, the data suggest that ivacaftor potentiates multiple gating mutants located in different parts of CFTR structure including R117H (M2), R668C (RD) and A1067T (ICL4) (Yu et al., 2012; Van Goor et al., 2014). Login to comment 1988 ABCC7 p.Arg117His ABCC7 p.Arg334Trp ABCC7 p.Arg347Pro 3.4. Class IV mutations: defective channel conduction Analysis of three CF-PS mutations located in MSD1 (R117H [M2], R334W [M6] and R347P [M6]) provided the first evidence that some CF mutations perturb anion flow through the CFTR pore (Fig. 3). Login to comment 1991 ABCC7 p.Arg117His For R117H, the reduction was Fig. 4. Login to comment 1993 ABCC7 p.Gly551Asp ABCC7 p.Gly1349Asp (A) Representative single-channel recordings of wild-type CFTR and the indicated CF mutants in excised inside-out membrane patches (number of active channels (N): wild-type and F508del-CFTR, N = 1; G1349D-CFTR, N = 2; G551D-CFTR, N > 4). Login to comment 1998 ABCC7 p.Arg334Trp ABCC7 p.Arg347Pro ~15%, but for R347P, it was ~70% and for R334W, discrete channel openings were not resolved (Sheppard et al., 1993). Login to comment 1999 ABCC7 p.Arg334Trp Later, Gong and Linsdell (2004) demonstrated that R334W reduced single-channel conductance by ~60% by impeding ion-ion interactions within the CFTR pore. Login to comment 2002 ABCC7 p.Arg334Leu ABCC7 p.Arg334Gln Mutation of R334, including the CF mutations R334L and R334Q, transformed the current-voltage (I-V) relationship of CFTR from linear (or quasi-linear, see Cai et al., 2003) to strongly inwardly rectifying (Smith et al., 2001; Gong and Linsdell, 2003). Login to comment 2005 ABCC7 p.Arg347His By contrast, the CF mutation R347H reduced single-channel conductance, converting CFTR to a single-ion pore. Login to comment 2011 ABCC7 p.Pro99Leu ABCC7 p.Pro99Leu For example, the CF mutation P99L, which affects a residue that faces away from the pore (Akabas et al., 1994; Gao et al., 2013, but see Wang et al., 2011), had an altered anion selectivity sequence (wild-type: Br- ࣙ Cl- > I-; P99L: Br- ࣙ Cl- = I-) and reduced single-channel conductance (Sheppard et al., 1996). Login to comment 2012 ABCC7 p.Arg117His Although the CF mutation R117H is classified as a class IV mutation, it is principally a gating mutation, reducing channel activity (measured by open probability [Po]) to ~30% wild-type levels, but single-channel conductance by only ~15% (Sheppard et al., 1993). Login to comment 2013 ABCC7 p.Arg117His Further analyses of the impact of R117H on CFTR channel gating are required. Login to comment 2014 ABCC7 p.Gly551Asp However, visual inspection of single-channel records suggests that the pattern of channel gating is different to that of G551D-CFTR, where the interburst interval is prolonged greatly (see Section 3.3). Login to comment 2015 ABCC7 p.Arg117His The data suggest that R117H destabilises the open-channel configuration with the result that the pattern of channel gating bears some resemblance to that of wild-type CFTR inhibited by intermediate speed open-channel blockers (e.g. glibenclamide; Sheppard and Robinson, 1997). Login to comment 2016 ABCC7 p.Arg117His Of note, H&#e4;mmerle et al. (2001) systematically investigated the impact of ten CF mutations in extracellular loop 1 (ECL1), including R117H, on CFTR expression and function. Login to comment 2017 ABCC7 p.Pro111Leu All the ECL1 CF mutants studied were correctly processed, some affected Cl-conductance and with the exception of P111L, all perturbed channel gating. Login to comment 2023 ABCC7 p.Gly178Arg ABCC7 p.His620Gln Interestingly, the authors demonstrated that G178R and H620Q, two CF-PI mutations that disrupt cellular HCO3 - transport, were without effect on CFTR-mediated HCO3 - transport, arguing that CF mutations influence HCO3 --transport indirectly. Login to comment 2026 ABCC7 p.Ala455Glu This class of CF mutations includes promoter mutations that alter transcription (e.g. 125 G࢐C), nucleotide changes that promote alterative splicing of CFTR transcripts (e.g. 3849 + 10 kb C࢐T) and amino acid substitutions, which cause inefficient protein maturation (e.g. A455E) (Zielenski and Tsui, 1995). Login to comment 2028 ABCC7 p.Ala455Glu This idea is exemplified by A455E, the first CF-PS mutation to be associated with milder lung disease (Gan et al., 1995). Login to comment 2029 ABCC7 p.Ala455Glu When studied in heterologous cells, A455E-CFTR disrupted the processing and intracellular transport of CFTR, albeit not as severely as F508del-CFTR (Sheppard et al., 1995). Login to comment 2030 ABCC7 p.Ala455Glu However, the conduction, permeation and gating properties of A455E-CFTR were almost indistinguishable from those of wild-type CFTR (Sheppard et al., 1995). Login to comment 2031 ABCC7 p.Pro574His Even more notable was the CF-PS mutation P574H, which disrupted CFTR processing, but formed a "super" normal channel, distinguished by greatly prolonged, but less frequent channel openings compared to wild-type CFTR (Sheppard et al., 1995; Champigny et al., 1995). Login to comment 2033 ABCC7 p.Gln1412* For example, the CF-PI mutation Q1412X, which truncates the last 70 amino acids of CFTR, generated macroscopic cAMP-stimulated Cl-currents with similar biophysical properties, but reduced magnitude compared to wild-type CFTR (Haardt et al., 1999). Login to comment 2034 ABCC7 p.Gln1412* ABCC7 p.Gln1412* Biochemical studies demonstrated that Q1412X was without effect on CFTR processing and intracellular transport, but greatly reduced the stability of mature CFTR protein (half-life in COS cells: wild-type CFTR, 14 h; Q1412X, 3.5 h). Login to comment