ABCMdb

ABCC7 p.Ser1248Phe

Predicted by SNAP2:	A: N (66%), C: D (66%), D: D (95%), E: D (95%), F: D (91%), G: D (85%), H: D (91%), I: D (91%), K: D (95%), L: D (91%), M: D (91%), N: D (91%), P: D (95%), Q: D (91%), R: D (95%), T: D (85%), V: D (91%), W: D (95%), Y: D (91%),
Predicted by PROVEAN:	A: N, C: N, D: D, E: N, F: D, G: N, H: D, I: D, K: N, L: D, M: D, N: D, P: D, Q: N, R: D, T: N, V: N, W: D, Y: D,

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[hide] Normal gating of CFTR requires ATP binding to both... Proc Natl Acad Sci U S A. 2005 Jan 11;102(2):455-60. Epub 2004 Dec 27. Berger AL, Ikuma M, Welsh MJ
Normal gating of CFTR requires ATP binding to both nucleotide-binding domains and hydrolysis at the second nucleotide-binding domain.
Proc Natl Acad Sci U S A. 2005 Jan 11;102(2):455-60. Epub 2004 Dec 27., 2005-01-11 [PMID:15623556]

Abstract [show]
ATP interacts with the two nucleotide-binding domains (NBDs) of CFTR to control gating. However, it is unclear whether gating involves ATP binding alone, or also involves hydrolysis at each NBD. We introduced phenylalanine residues into nonconserved positions of each NBD Walker A motif to sterically prevent ATP binding. These mutations blocked [alpha-(32)P]8-N(3)-ATP labeling of the mutated NBD and reduced channel opening rate without changing burst duration. Introducing cysteine residues at these positions and modifying with N-ethylmaleimide produced the same gating behavior. These results indicate that normal gating requires ATP binding to both NBDs, but ATP interaction with one NBD is sufficient to support some activity. We also studied mutations of the conserved Walker A lysine residues (K464A and K1250A) that prevent hydrolysis. By combining substitutions that block ATP binding with Walker A lysine mutations, we could differentiate the role of ATP binding vs. hydrolysis at each NBD. The K1250A mutation prolonged burst duration; however, blocking ATP binding prevented the long bursts. These data indicate that ATP binding to NBD2 allowed channel opening and that closing was delayed in the absence of hydrolysis. The corresponding NBD1 mutations showed relatively little effect of preventing ATP hydrolysis but a large inhibition of blocking ATP binding. These data suggest that ATP binding to NBD1 is required for normal activity but that hydrolysis has little effect. Our results suggest that both NBDs contribute to channel gating, NBD1 binds ATP but supports little hydrolysis, and ATP binding and hydrolysis at NBD2 are key for normal gating.

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No. Sentence Comment
103 The A462F mutation prevented labeling of NBD1; S1248F blocked NBD2 labeling; and the double mutant A462F͞S1248F abolished labeling at both NBDs. Login to comment
110 The S1248F mutation reduced Po by prolonging the interburst interval without altering burst duration (Fig. 2 A and C). Login to comment
113 In addition, correspondence of the S1248F and NEM-modified S1248C data indicate that the gating effects of the S1248F substitution were not due to misfolding that might have occurred during channel biosynthesis. Login to comment
127 (A) Examples of single-channel recordings for WT and S1248F CFTR. Login to comment
140 The finding that channels unable to bind nucleotide at NBD2 (S1248F and NEM-modified S1248C) had a normal burst duration suggested that the prolonged burst duration of K1250A (16-18, 20, 21) arose when ATP bound NBD2 but then did not undergo hydrolysis. Login to comment
143 However, when we modified NBD2 with NEM to prevent nucleotide binding, burst duration fell into the range of WT or S1248F channels (compare Figs. Login to comment
172 The S1248F mutation will block NBD2 ATP binding, thereby limiting ATP interactions to NBD1, and the K464A mutation will prevent NBD1 ATP hydrolysis. Login to comment
174 However with ATP, the Po, interburst interval, and burst duration were similar to those obtained with the S1248F mutation alone (Figs. Login to comment
203 Second, the K464A͞S1248F mutant behaved similarly to the S1248F single mutation. Login to comment
221 Our results argue against this explanation because blocking NBD2 ATP binding (with either the S1248F mutation or NEM-modification of S1248C) did not prolong burst duration. Login to comment
233 However, it seems surprising that blocking ATP binding to NBD2 (with the S1248F mutation or the NEM-modified S1248C mutation) did not change the rate of channel closure compared to WT. Login to comment
250 However, that is not what we observed; the A462F mutation completely blocked NBD1 labeling, and S1248F blocked NBD2 labeling. Login to comment
253 Nevertheless, we did find that the A462F mutation in NBD1 diminished labeling of NBD2 and that S1248F slightly reduced NBD1 labeling. Login to comment

[hide] Demonstration of Phosphoryl Group Transfer Indicat... J Biol Chem. 2012 Oct 19;287(43):36105-10. doi: 10.1074/jbc.M112.408450. Epub 2012 Sep 4. Randak CO, Ver Heul AR, Welsh MJ
Demonstration of Phosphoryl Group Transfer Indicates That the ATP-binding Cassette (ABC) Transporter Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) Exhibits Adenylate Kinase Activity.
J Biol Chem. 2012 Oct 19;287(43):36105-10. doi: 10.1074/jbc.M112.408450. Epub 2012 Sep 4., [PMID:22948143]

Abstract [show]
Cystic fibrosis transmembrane conductance regulator (CFTR) is a membrane-spanning adenosine 5'-triphosphate (ATP)-binding cassette (ABC) transporter. ABC transporters and other nuclear and cytoplasmic ABC proteins have ATPase activity that is coupled to their biological function. Recent studies with CFTR and two nonmembrane-bound ABC proteins, the DNA repair enzyme Rad50 and a structural maintenance of chromosome (SMC) protein, challenge the model that the function of all ABC proteins depends solely on their associated ATPase activity. Patch clamp studies indicated that in the presence of physiologically relevant concentrations of adenosine 5'-monophosphate (AMP), CFTR Cl(-) channel function is coupled to adenylate kinase activity (ATP+AMP &lrarr2; 2 ADP). Work with Rad50 and SMC showed that these enzymes catalyze both ATPase and adenylate kinase reactions. However, despite the supportive electrophysiological results with CFTR, there are no biochemical data demonstrating intrinsic adenylate kinase activity of a membrane-bound ABC transporter. We developed a biochemical assay for adenylate kinase activity, in which the radioactive gamma-phosphate of a nucleotide triphosphate could transfer to a photoactivatable AMP analog. UV irradiation could then trap the (32)P on the adenylate kinase. With this assay, we discovered phosphoryl group transfer that labeled CFTR, thereby demonstrating its adenylate kinase activity. Our results also suggested that the interaction of nucleotide triphosphate with CFTR at ATP-binding site 2 is required for adenylate kinase activity. These biochemical data complement earlier biophysical studies of CFTR and indicate that the ABC transporter CFTR can function as an adenylate kinase.

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No. Sentence Comment
56 CFTR Adenylate Kinase Assay-Membranes containing either 30 ␮g of protein (from cells expressing wild-type CFTR) or 90 ␮g of protein (from cells expressing S1248F CFTR) were incubated gently shaking with nonradioactive 8- or 2-N3-AMP (at concentrations given in the figure legends), radioactive [␥-32 P]GTP (30 ␮Ci, 6000 Ci/mmol), 20 mM Hepes (pH 7.5), 50 mM NaCl, 3 mM MgCl2, and 1 mM Tricine (pH 7.6) for 5 min at 37 °C in a total volume of 30 ␮l followed by UV irradiation for 30 s (302 nm, 8-watt lamp) at a distance of 5 cm. Login to comment
137 We chose a phenylalanine substitution for serine at position 1248 (S1248F) in the phosphate-binding loop of ATP-binding site 2. Login to comment
151 In lane 6, membranes containing 90 ␮g of protein from S1248F CFTR-expressing HeLa cells were employed. Login to comment
161 30 ␮g (control membranes and membranes with wild-type CFTR, lanes 1-3) and 90 ␮g (membranes with S1248F CFTR, lane 4) of protein were used. Login to comment
163 When we incubated membranes containing S1248F CFTR with [␥-32 P]GTP and nonradioactive N3-AMP, followed by UV irradiation, we found very little labeling (Fig. 4A, lane 6). Login to comment
178 Substituting a phenylalanine into the phosphate-binding loop of NBD2 (the S1248F mutation) interfered with labeling. Login to comment
180 Previous observations support the interpretation that the S1248F mutation disrupted adenylate kinase activity. Login to comment
181 1) A study characterizing the gating characteristics and the interaction of ATP with S1248F CFTR found that this mutation interfered with the interaction of nucleotides at ATP-binding site 2. Login to comment
57 CFTR Adenylate Kinase Assay-Membranes containing either 30 òe;g of protein (from cells expressing wild-type CFTR) or 90 òe;g of protein (from cells expressing S1248F CFTR) were incubated gently shaking with nonradioactive 8- or 2-N3-AMP (at concentrations given in the figure legends), radioactive [ॹ-32 P]GTP (30 òe;Ci, 6000 Ci/mmol), 20 mM Hepes (pH 7.5), 50 mM NaCl, 3 mM MgCl2, and 1 mM Tricine (pH 7.6) for 5 min at 37 &#b0;C in a total volume of 30 òe;l followed by UV irradiation for 30 s (302 nm, 8-watt lamp) at a distance of 5 cm. Login to comment
136 We chose a phenylalanine substitution for serine at position 1248 (S1248F) in the phosphate-binding loop of ATP-binding site 2. Login to comment
150 In lane 6, membranes containing 90 òe;g of protein from S1248F CFTR-expressing HeLa cells were employed. Login to comment
160 30 òe;g (control membranes and membranes with wild-type CFTR, lanes 1-3) and 90 òe;g (membranes with S1248F CFTR, lane 4) of protein were used. Login to comment
162 When we incubated membranes containing S1248F CFTR with [ॹ-32 P]GTP and nonradioactive N3-AMP, followed by UV irradiation, we found very little labeling (Fig. 4A, lane 6). Login to comment

[hide] ATP and AMP mutually influence their interaction w... J Biol Chem. 2013 Sep 20;288(38):27692-701. doi: 10.1074/jbc.M113.479675. Epub 2013 Aug 6. Randak CO, Dong Q, Ver Heul AR, Elcock AH, Welsh MJ
ATP and AMP mutually influence their interaction with the ATP-binding cassette (ABC) adenylate kinase cystic fibrosis transmembrane conductance regulator (CFTR) at separate binding sites.
J Biol Chem. 2013 Sep 20;288(38):27692-701. doi: 10.1074/jbc.M113.479675. Epub 2013 Aug 6., [PMID:23921386]

Abstract [show]
Cystic fibrosis transmembrane conductance regulator (CFTR) is an anion channel in the ATP-binding cassette (ABC) transporter protein family. In the presence of ATP and physiologically relevant concentrations of AMP, CFTR exhibits adenylate kinase activity (ATP + AMP &lrarr2; 2 ADP). Previous studies suggested that the interaction of nucleotide triphosphate with CFTR at ATP-binding site 2 is required for this activity. Two other ABC proteins, Rad50 and a structural maintenance of chromosome protein, also have adenylate kinase activity. All three ABC adenylate kinases bind and hydrolyze ATP in the absence of other nucleotides. However, little is known about how an ABC adenylate kinase interacts with ATP and AMP when both are present. Based on data from non-ABC adenylate kinases, we hypothesized that ATP and AMP mutually influence their interaction with CFTR at separate binding sites. We further hypothesized that only one of the two CFTR ATP-binding sites is involved in the adenylate kinase reaction. We found that 8-azidoadenosine 5'-triphosphate (8-N3-ATP) and 8-azidoadenosine 5'-monophosphate (8-N3-AMP) photolabeled separate sites in CFTR. Labeling of the AMP-binding site with 8-N3-AMP required the presence of ATP. Conversely, AMP enhanced photolabeling with 8-N3-ATP at ATP-binding site 2. The adenylate kinase active center probe P(1),P(5)-di(adenosine-5') pentaphosphate interacted simultaneously with an AMP-binding site and ATP-binding site 2. These results show that ATP and AMP interact with separate binding sites but mutually influence their interaction with the ABC adenylate kinase CFTR. They further indicate that the active center of the adenylate kinase comprises ATP-binding site 2.

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Sentences [show]
No. Sentence Comment
239 Substituting serine at position 1248 in NBD2 with phenylalanine (S1248F mutation; Fig. 9C, left) abolished nucleotide interaction with ATP-binding site 2. Login to comment
241 The A462F, but not the S1248F mutation interfered with processing and trafficking to the cell membrane (supplemental Fig. S1), and hence, the number of channels in excised membrane patches was small; therefore, we quantified channel activity as NPo. Login to comment
243 On the other hand, Ap5A had no effect on ATP-dependent current of S1248F CFTR (Fig. 9C, middle and right). Login to comment
270 C, left, model of S1248F CFTR. Login to comment
272 Middle, current recording (100 ms averages) from an excised inside-out membrane patch containing multiple S1248F CFTR channels. ATP and Ap5A were present during the times and at the concentrations indicated by bars. Login to comment
273 ATP was added together with PKA catalytic subunit. Holding voltage was afa;80 mV. Right, S1248F CFTR Clafa; current before and after adding 1 mM Ap5A. Experiments were performed as shown in the middle panel with 0.3 mM ATP and PKA present. Login to comment
301 (a) The S1248F mutation, which interfered with the binding of ATP to site 2 (15) and abolished the inhibition of CFTR current in the presence of Ap5A in our study (Fig. 9C), also disrupted CFTR adenylate kinase activity (22). Login to comment

[hide] Mutating the Conserved Q-loop Glutamine 1291 Selec... J Biol Chem. 2015 May 29;290(22):14140-53. doi: 10.1074/jbc.M114.611616. Epub 2015 Apr 17. Dong Q, Ernst SE, Ostedgaard LS, Shah VS, Ver Heul AR, Welsh MJ, Randak CO
Mutating the Conserved Q-loop Glutamine 1291 Selectively Disrupts Adenylate Kinase-dependent Channel Gating of the ATP-binding Cassette (ABC) Adenylate Kinase Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) and Reduces Channel Function in Primary Human Airway Epithelia.
J Biol Chem. 2015 May 29;290(22):14140-53. doi: 10.1074/jbc.M114.611616. Epub 2015 Apr 17., [PMID:25887396]

Abstract [show]
The ATP-binding cassette (ABC) transporter cystic fibrosis transmembrane conductance regulator (CFTR) and two other non-membrane-bound ABC proteins, Rad50 and a structural maintenance of chromosome (SMC) protein, exhibit adenylate kinase activity in the presence of physiologic concentrations of ATP and AMP or ADP (ATP + AMP left arrow over right arrow 2 ADP). The crystal structure of the nucleotide-binding domain of an SMC protein in complex with the adenylate kinase bisubstrate inhibitor P(1),P(5)-di(adenosine-5') pentaphosphate (Ap5A) suggests that AMP binds to the conserved Q-loop glutamine during the adenylate kinase reaction. Therefore, we hypothesized that mutating the corresponding residue in CFTR, Gln-1291, selectively disrupts adenylate kinase-dependent channel gating at physiologic nucleotide concentrations. We found that substituting Gln-1291 with bulky side-chain amino acids abolished the effects of Ap5A, AMP, and adenosine 5'-monophosphoramidate on CFTR channel function. 8-Azidoadenosine 5'-monophosphate photolabeling of the AMP-binding site and adenylate kinase activity were disrupted in Q1291F CFTR. The Gln-1291 mutations did not alter the potency of ATP at stimulating current or ATP-dependent gating when ATP was the only nucleotide present. However, when physiologic concentrations of ADP and AMP were added, adenylate kinase-deficient Q1291F channels opened significantly less than wild type. Consistent with this result, we found that Q1291F CFTR displayed significantly reduced Cl(-) channel function in well differentiated primary human airway epithelia. These results indicate that a highly conserved residue of an ABC transporter plays an important role in adenylate kinase-dependent CFTR gating. Furthermore, the results suggest that adenylate kinase activity is important for normal CFTR channel function in airway epithelia.

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Sentences [show]
No. Sentence Comment
165 As a positive control, we mutated serine 1248 to phenylalanine (S1248F) in Q1291F CFTR.TheS1248FmutationpreventstheinteractionofATPwith ATP-bindingsite2(48).Asanticipated,theopenprobabilityofthe double mutant was markedly reduced, mainly due to interburst closed times that were significantly longer than those of wild-type andQ1291FCFTR(comparebar6withbars1and5inthetopand bottom panels of Fig. 5B). Login to comment
207 Holding voltage was afa;80 mV for wild-type, Q1291W, and Q1291Y CFTR and afa;60 mV for Q1291H, Q1291F, and Q1291F/S1248F CFTR. Login to comment