ABCMdb

ABCC7 p.Thr908Asn

ClinVar:	c.2723C>A , p.Thr908Asn ? , not provided
CF databases:	c.2723C>A , p.Thr908Asn (CFTR1) D , Found by DGGE and DNA sequencing. (CBAVD patient, genotype [delta]F508/T908N)
Predicted by SNAP2:	A: N (72%), C: N (57%), D: N (78%), E: N (82%), F: N (53%), G: N (72%), H: N (61%), I: N (57%), K: N (72%), L: N (61%), M: N (61%), N: N (78%), P: N (61%), Q: N (82%), R: N (61%), S: N (82%), V: N (61%), W: N (57%), Y: N (57%),
Predicted by PROVEAN:	A: N, C: N, D: N, E: N, F: N, G: N, H: N, I: N, K: N, L: N, M: N, N: N, P: N, Q: N, R: N, S: N, V: N, W: N, Y: N,

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[hide] Disease-associated mutations in the extracytoplasm... J Biol Chem. 2001 May 4;276(18):14848-54. Epub 2001 Feb 6. Hammerle MM, Aleksandrov AA, Riordan JR
Disease-associated mutations in the extracytoplasmic loops of cystic fibrosis transmembrane conductance regulator do not impede biosynthetic processing but impair chloride channel stability.
J Biol Chem. 2001 May 4;276(18):14848-54. Epub 2001 Feb 6., 2001-05-04 [PMID:11278813]

Abstract [show]
Consistent with its function as a chloride channel regulated entirely from the cytoplasmic side of the plasma membrane, the cystic fibrosis transmembrane conductance regulator (CFTR) glycoprotein exposes little of its mass on the exterior surface of cells. The first and fourth extracytoplasmic loops (ELs) contain approximately 15 and 30 residues, respectively; the other four ELs are extremely short. To examine the influence of missense mutants in ELs detected in patients with cystic fibrosis, we have expressed them in mammalian (baby hamster kidney (BHK21)) cells and assessed their biosynthetic processing and chloride channel activity. In contrast to previous findings that 18 of 30 disease-associated missense mutations in cytoplasmic loops caused retention of the nascent polypeptides in the endoplasmic reticulum, all the EL mutants studied matured and were transported to the cell surface. This pronounced asymmetry is consistent with the notion that endoplasmic reticulum quality control of nascent CFTR is exerted primarily on the cytoplasmic side of the membrane. Although this set of EL mutations has little effect on CFTR maturation, most of them seriously compromise its chloride channel activity. Substitutions at six different positions in EL1 and single positions in EL2 and EL4 all destabilized the open state, some of them severely, indicating that the ELs contribute to the stability of the CFTR ion pore.

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No. Sentence Comment
75 TABLE I Oligonucleotide primers used to generate mutations Mutation Primer S108F GGAAGAATCATAGCTTtCTATGACCCGGATAAC Y109C AGAATCATAGCTTCCTgTGACCCGGATAACAAG D110H ATCATAGCTTCCTATcACCCGGATAACAAGGAG P111A ATAGCTTCCTATGACgCGGATAACAAGGAGGAA P111L ATAGCTTCCTATGACCtGGATAACAAGGAGGAA E116K CCGGATAACAAGGAGaAACGCTCTATCGCGATT R117C GATAACAAGGAGGAAtGCTCTATCGCGATTTAT R117H GATAACAAGGAGGAACaCTCTATCGCGATTTAT R117L GATAACAAGGAGGAACtCTCTATCGCGATTTAT R117P GATAACAAGGAGGAACcCTCTATCGCGATTTAT E217G ATGGGGCTAATCTGGGgGTTGTTACAGGCGTCT T908N TATGCAGTGATTATCAaCAGCACCAGTTCGTAT P1013L GTCGCAGTTTTACAACtCTACATCTTTGTTGCA FIG. 2. Login to comment
91 Exceptions are S108F, which matures as efficiently as the wild type, and T908N, which matures even more efficiently. Login to comment
120 D, squares, E217G; circles, T908N; triangles, P1013L. Login to comment
153 The T908N mutation in EL4, the second of the two larger extracytoplasmic loops of CFTR, has a somewhat similar effect on the single channel behavior as those in EL1 that cause a very unstable open state. Login to comment
156 As seen in the T908N trace, there are in fact relatively long openings with several brief closings within to generate burstlike behavior. Login to comment
171 For example a nucleotide binding domain mutation, G551D, precludes virtually all TABLE II Relative charge transport capacity of mutants Mutants S108F Y109C D110H P111L P111A E116K R117H R117C R117L R117P E217G T908N P1013L Imutant/Iwt 100% 11 15 27 173 105 12 80 27 5 11 10 48 170 FIG. 5. Login to comment
190 The T908N mutation in EL4, which is novel in that it results in the introduction of an additional consensus site for N-glycosylation that is used (17), also alters channel gating. Login to comment

[hide] A novel CFTR disease-associated mutation causes ad... Glycoconj J. 2000 Nov;17(11):807-13. Hammerle MM, Aleksandrov AA, Chang XB, Riordan JR
A novel CFTR disease-associated mutation causes addition of an extra N-linked oligosaccharide.
Glycoconj J. 2000 Nov;17(11):807-13., [PMID:11443282]

Abstract [show]
We have examined the influence of a novel missense mutation in the fourth extracytoplasmic loop (EL4) of CFTR detected in a patient with cystic fibrosis. This substitution (T908N) creates a consensus sequence (N X S/T) for addition of an N-linked oligosaccharide chain near the C-terminal end of EL4. Oligosaccharyl transferase generally does not have access to this consensus sequence if it is closer than about twelve amino acids from the membrane. However, the T908N site is used, even though it is within four residues of the predicted membrane interface and the oligosaccharide chain added binds calnexin, a resident chaperone of the ER membrane. The chloride channel activity of this variant CFTR is abnormal as evidenced by a reduced rate of (36)Cl(-) efflux and a noisy single channel open state. This may reflect some displacement of the membrane spanning sequence C-terminal of EL4 since it contains residues influencing the ion pore.

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3 This substitution (T908N) creates a consensus sequence (N X S=T) for addition of an N-linked oligosaccharide chain near the C-terminal end of EL4. Login to comment
5 However, the T908N site is used, even though it is within four residues of the predicted membrane interface and the oligosaccharide chain added binds calnexin, a resident chaperone of the ER membrane. Login to comment
13 However, while analyzing the functional impact of missense mutations in the putative extracytoplasmic loops (ELs) of the protein [7], we realized that one (T908N) created a consensus sequence (N X S=T) for N-glycosylation. Login to comment
20 BHK cells stably expressing T908N-CFTR were similarly established. Login to comment
23 Tel.: 480-301-6206; Fax: 480-301-7017; E-mail: riordan@mayo.edu N900D, T908N or T910N to produce a CFTR with different numbers or no consensus site for glycosylation on extracytoplasmic loop 4. Login to comment
46 Single channel records Microsomal vesicles were isolated from BHK cells expressing wildtype and T908N CFTR and phosphorylated with protein kinase A [17]. Login to comment
52 Reconstruction and expression of the T908N variant in BHK cells resulted in the synthesis of a protein which ran with reduced mobility in SDS-PAGE (Figure 1B) consistent with the possibility that this additional N-glycosylation site had been used. Login to comment
54 The sialidase treatment increased the mobility of both the wild-type and the T908N variant substantially, indicating that the oligosaccharide chains are highly sialylated. Login to comment
55 After N-glycosidase F treatment the mobility is increased further and the deglycosylated form of both the wild-type and T908N migrate to the same position. Login to comment
57 The difference in mobility between wild-type and T908N was entirely eliminated after cells were grown in presence of the inhibitor. Login to comment
60 (A) Sketch of CFTR topology indicating position of T908N relative to the membrane and native glycosylation sites at N894 and N900. Login to comment
61 (B) Cells stably expressing wild type and T908N-CFTR were lysed in NP-40 lysis buffer (see Materials and methods). Login to comment
65 Cells expressing wild-type and T908N-CFTR were pulse labeled and chased as described in Methods. oligosaccharyl transferase and is an acceptor of an N-linked oligosaccharide chain. Login to comment
69 Conversion of precursor to product occurs with low efficiency ($ 30%) but this also is similar with wild-type and the T908N variant. Login to comment
70 Hence the additional oligosaccharide in T908N does not have a profound effect on the biosynthetic processing of CFTR. Login to comment
89 As already noted in Figure 1 the T908N variant in the wild-type background has substantially decreased mobility. Login to comment
98 T908N reduces the rate of 36 Cl7 efflux and alters both the single channel gating kinetics and conductance of CFTR. Login to comment
108 As shown in Figure 1B, removal of sialic acid from complex glycosylated CFTR results in a higher mobility of wild-type and T908N. Login to comment
114 Similar amounts of calnexin were detected in CFTR immunoprecipitates containing wild-type and T908N, and 894N and 900N alone whereas much less was detected when single oligosaccharide chains were present at 908N and especially at 910N (Figure 3). Login to comment
116 To assess how the presence of a third oligosaccharide chain influences CFTR function, the rate of 36 Cl7 efflux from cells expressing the T908N variant was compared with wild-type and was found to be reduced about 50% (Figure 4A). Login to comment
119 Thus both measures of the T908N CFTR chloride channel indicate that while still active, it is substantially altered from the wild-type. Login to comment
120 Discussion Although all types of mutations have been detected in the CFTR gene of patients with cystic fibrosis, T908N is the only example of a single residue substitution that introduces a consensus site for glycosylation. Login to comment

[hide] Identification of CFTR, PRSS1, and SPINK1 mutation... Pancreas. 2006 Oct;33(3):221-7. Keiles S, Kammesheidt A
Identification of CFTR, PRSS1, and SPINK1 mutations in 381 patients with pancreatitis.
Pancreas. 2006 Oct;33(3):221-7., [PMID:17003641]

Abstract [show]
OBJECTIVES: Chronic pancreatitis is a progressive inflammatory disorder leading to irreversible exocrine and/or endocrine impairment. It is well documented that mutations in the cationic trypsinogen (PRSS1) gene can cause hereditary pancreatitis. Mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) and the serine protease inhibitor Kazal type 1 (SPINK1) genes are also associated with pancreatitis. METHODS: We analyzed 381 patients with a primary diagnosis of chronic or recurrent pancreatitis using the Ambry Test: Pancreatitis to obtain comprehensive genetic information for the CFTR, SPINK1, and PRSS1 genes. RESULTS: The results identified 32% (122/381) of patients with 166 mutant CFTR alleles, including 12 novel CFTR variants: 4375-20 A>G, F575Y, K598E, L1260P, G194R, F834L, S573C, 2789 + 17 C>T, 621+83 A>G, T164S, 621+25 A>G, and 3500-19 G>A. Of 122 patients with CFTR mutations, 5.5% (21/381) also carried a SPINK1 mutation, and 1.8% (7/381) carried a PRSS1 mutation. In addition, 8.9% (34/381) of all patients had 1 of 11 different SPINK1 mutations. Another 6.3% (24/381) of the patients had 1 of 8 different PRSS1 mutations. Moreover, 1.3% of the patients (5/381) had 1 PRSS1 and 1 SPINK1 mutation. A total 49% (185/381) of the patients carried one or more mutations. CONCLUSIONS: Comprehensive testing of the CFTR, PRSS1, and SPINK1 genes identified genetic variants in nearly half of all subjects considered by their physicians as candidates for genetic testing. Comprehensive test identified numerous novel variants that would not be identified by standard clinical screening panels.

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112 However, this patient also carries a T908N mutation in the CFTR gene. Login to comment
116 Patients With CFTR and PRSS1 Mutations CFTR Mutation 1 CFTR Mutation 2 PRSS1 Mutation 1 PRSS1 Mutation 2 No. of Patients 5T E79K 1 5T R122H 1 2789+17 C9T C139S 1 deltaF508 N29I 1 deltaF508 Q1352H G208A G208A 1 G551D R122H 1 T908N IVS4-8 C9T IVS4-11 C9T 1 Total patients 7 CFTR mutations in boldface would not have been detected by the ACOG/ACMG mutation panel. Login to comment

[hide] N-glycans are direct determinants of CFTR folding ... J Cell Biol. 2009 Mar 23;184(6):847-62. Glozman R, Okiyoneda T, Mulvihill CM, Rini JM, Barriere H, Lukacs GL
N-glycans are direct determinants of CFTR folding and stability in secretory and endocytic membrane traffic.
J Cell Biol. 2009 Mar 23;184(6):847-62., 2009-03-23 [PMID:19307599]

Abstract [show]
N-glycosylation, a common cotranslational modification, is thought to be critical for plasma membrane expression of glycoproteins by enhancing protein folding, trafficking, and stability through targeting them to the ER folding cycles via lectin-like chaperones. In this study, we show that N-glycans, specifically core glycans, enhance the productive folding and conformational stability of a polytopic membrane protein, the cystic fibrosis transmembrane conductance regulator (CFTR), independently of lectin-like chaperones. Defective N-glycosylation reduces cell surface expression by impairing both early secretory and endocytic traffic of CFTR. Conformational destabilization of the glycan-deficient CFTR induces ubiquitination, leading to rapid elimination from the cell surface. Ubiquitinated CFTR is directed to lysosomal degradation instead of endocytic recycling in early endosomes mediated by ubiquitin-binding endosomal sorting complex required for transport (ESCRT) adaptors Hrs (hepatocyte growth factor-regulated tyrosine kinase substrate) and TSG101. These results suggest that cotranslational N-glycosylation can exert a chaperone-independent profolding change in the energetic of CFTR in vivo as well as outline a paradigm for the peripheral trafficking defect of membrane proteins with impaired glycosylation.

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263 In accord, with the localized effect of the glycan chain, partial reversion of the expression and folding defect of the 900D- and 2D-CFTR was observed by introducing a validated glycosylation site (T908N) in the fourth extracellular loop (Hammerle et al., 2000; Fig. S5). Login to comment

[hide] Do common in silico tools predict the clinical con... Clin Genet. 2010 May;77(5):464-73. Epub 2009 Jan 6. Dorfman R, Nalpathamkalam T, Taylor C, Gonska T, Keenan K, Yuan XW, Corey M, Tsui LC, Zielenski J, Durie P
Do common in silico tools predict the clinical consequences of amino-acid substitutions in the CFTR gene?
Clin Genet. 2010 May;77(5):464-73. Epub 2009 Jan 6., [PMID:20059485]

Abstract [show]
Computational methods are used to predict the molecular consequences of amino-acid substitutions on the basis of evolutionary conservation or protein structure, but their utility in clinical diagnosis or prediction of disease outcome has not been well validated. We evaluated three popular computer programs, namely, PANTHER, SIFT and PolyPhen, by comparing the predicted clinical outcomes for a group of known CFTR missense mutations against the diagnosis of cystic fibrosis (CF) and clinical manifestations in cohorts of subjects with CF-disease and CFTR-related disorders carrying these mutations. Owing to poor specificity, none of tools reliably distinguished between individual mutations that confer CF disease from mutations found in subjects with a CFTR-related disorder or no disease. Prediction scores for CFTR mutations derived from PANTHER showed a significant overall statistical correlation with the spectrum of disease severity associated with mutations in the CFTR gene. In contrast, PolyPhen- and SIFT-derived scores only showed significant differences between CF-causing and non-CF variants. Current computational methods are not recommended for establishing or excluding a CF diagnosis, notably as a newborn screening strategy or in patients with equivocal test results.

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No. Sentence Comment
64 Mutations in the CFTR gene grouped by clinical category Cystic fibrosis CFTR-related disease No disease T338I D614G L320V V920L L90S M470V H199R S1251N I203M G550R P111A I148T Q1291H R560K L1388Q L183I R170H I1027T S549R D443Y P499A L1414S T908N R668C S549N A455E E1401K Q151K G27E I1234L Y563N R347P C866R S1118C P1290S R75Q A559T V520F P841R M469V E1401G P67L G85E S50Y E1409K R933G G458V G178R Y1032C R248T I980K G85V V392G L973P L137H T351S R334W I444S V938G R792G R560T R555G L1339F D1305E P574H V1240G T1053I D58G G551D L1335P I918M F994C S945L L558S F1337V R810G D1152H G1247R P574S R766M D579G W1098R H949R F200I R352Q L1077P K1351E M244K L206W M1101K D1154G L375F N1303K R1066C E528D D110Y R347H R1070Q A800G P1021S S549K A1364V V392A damaging` (is supposed to affect protein function or structure) and 'probably damaging` (high confidence of affecting protein function or structure). Login to comment

[hide] Spectrum of CFTR mutations in cystic fibrosis and ... Hum Mutat. 2000;16(2):143-56. Claustres M, Guittard C, Bozon D, Chevalier F, Verlingue C, Ferec C, Girodon E, Cazeneuve C, Bienvenu T, Lalau G, Dumur V, Feldmann D, Bieth E, Blayau M, Clavel C, Creveaux I, Malinge MC, Monnier N, Malzac P, Mittre H, Chomel JC, Bonnefont JP, Iron A, Chery M, Georges MD
Spectrum of CFTR mutations in cystic fibrosis and in congenital absence of the vas deferens in France.
Hum Mutat. 2000;16(2):143-56., [PMID:10923036]

Abstract [show]
We have collated the results of cystic fibrosis (CF) mutation analysis conducted in 19 laboratories in France. We have analyzed 7, 420 CF alleles, demonstrating a total of 310 different mutations including 24 not reported previously, accounting for 93.56% of CF genes. The most common were F508del (67.18%; range 61-80), G542X (2.86%; range 1-6.7%), N1303K (2.10%; range 0.75-4.6%), and 1717-1G>A (1.31%; range 0-2.8%). Only 11 mutations had relative frequencies >0. 4%, 140 mutations were found on a small number of CF alleles (from 29 to two), and 154 were unique. These data show a clear geographical and/or ethnic variation in the distribution of the most common CF mutations. This spectrum of CF mutations, the largest ever reported in one country, has generated 481 different genotypes. We also investigated a cohort of 800 French men with congenital bilateral absence of the vas deferens (CBAVD) and identified a total of 137 different CFTR mutations. Screening for the most common CF defects in addition to assessment for IVS8-5T allowed us to detect two mutations in 47.63% and one in 24.63% of CBAVD patients. In a subset of 327 CBAVD men who were more extensively investigated through the scanning of coding/flanking sequences, 516 of 654 (78. 90%) alleles were identified, with 15.90% and 70.95% of patients carrying one or two mutations, respectively, and only 13.15% without any detectable CFTR abnormality. The distribution of genotypes, classified according to the expected effect of their mutations on CFTR protein, clearly differed between both populations. CF patients had two severe mutations (87.77%) or one severe and one mild/variable mutation (11.33%), whereas CBAVD men had either a severe and a mild/variable (87.89%) or two mild/variable (11.57%) mutations.

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152 Twenty-four non F508del mutations were found associated with the 9T allele: 394delTT, L90S, D110H, R117G, 621+1G>T, V232D, A455E, G542X, R851L, T908N, 2789+5G>A, 2896insAG, H939R, 3007delG, I980K, I1027T, R1066H, A1067T, D1154G, 3737delA, R74W+D1270N, N1303I, N1303K, D1377H. Login to comment

[hide] Mechanisms of CFTR Folding at the Endoplasmic Reti... Front Pharmacol. 2012 Dec 13;3:201. doi: 10.3389/fphar.2012.00201. eCollection 2012. Kim SJ, Skach WR
Mechanisms of CFTR Folding at the Endoplasmic Reticulum.
Front Pharmacol. 2012 Dec 13;3:201. doi: 10.3389/fphar.2012.00201. eCollection 2012., [PMID:23248597]

Abstract [show]
In the past decade much has been learned about how Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) folds and misfolds as the etiologic cause of cystic fibrosis (CF). CFTR folding is complex and hierarchical, takes place in multiple cellular compartments and physical environments, and involves several large networks of folding machineries. Insertion of transmembrane (TM) segments into the endoplasmic reticulum (ER) membrane and tertiary folding of cytosolic domains begin cotranslationally as the nascent polypeptide emerges from the ribosome, whereas posttranslational folding establishes critical domain-domain contacts needed to form a physiologically stable structure. Within the membrane, N- and C-terminal TM helices are sorted into bundles that project from the cytosol to form docking sites for nucleotide binding domains, NBD1 and NBD2, which in turn form a sandwich dimer for ATP binding. While tertiary folding is required for domain assembly, proper domain assembly also reciprocally affects folding of individual domains analogous to a jig-saw puzzle wherein the structure of each interlocking piece influences its neighbors. Superimposed on this process is an elaborate proteostatic network of cellular chaperones and folding machineries that facilitate the timing and coordination of specific folding steps in and across the ER membrane. While the details of this process require further refinement, we finally have a useful framework to understand key folding defect(s) caused by DeltaF508 that provides a molecular target(s) for the next generation of CFTR small molecule correctors aimed at the specific defect present in the majority of CF patients.

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No. Sentence Comment
96 The CF mutation T908N, however, creates a glycosylation site that is recognized by OST even though it is only four-residues from the predicted N-terminus of TM8. Login to comment