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Kleizen B, van Willigen M, Mijnders M, Peters F, Grudniewska M, Hillenaar T, Thomas A, Kooijman L, Peters KW, Frizzell R, van der Sluijs P, Braakman I. Co-Translational Folding of the First Transmembrane Domain of ABC-Transporter CFTR is Supported by Assembly with the First Cytosolic Domain. J Mol Biol 2021; 433:166955. [PMID: 33771570 DOI: 10.1016/j.jmb.2021.166955] [Citation(s) in RCA: 25] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2020] [Revised: 03/16/2021] [Accepted: 03/16/2021] [Indexed: 11/29/2022]
Abstract
ABC transporters transport a wealth of molecules across membranes and consist of transmembrane and cytosolic domains. Their activity cycle involves a tightly regulated and concerted domain choreography. Regulation is driven by the cytosolic domains and function by the transmembrane domains. Folding of these polytopic multidomain proteins to their functional state is a challenge for cells, which is mitigated by co-translational and sequential events. We here reveal the first stages of co-translational domain folding and assembly of CFTR, the ABC transporter defective in the most abundant rare inherited disease cystic fibrosis. We have combined biosynthetic radiolabeling with protease-susceptibility assays and domain-specific antibodies. The most N-terminal domain, TMD1 (transmembrane domain 1), folds both its hydrophobic and soluble helices during translation: the transmembrane helices pack tightly and the cytosolic N- and C-termini assemble with the first cytosolic helical loop ICL1, leaving only ICL2 exposed. This N-C-ICL1 assembly is strengthened by two independent events: (i) assembly of ICL1 with the N-terminal subdomain of the next domain, cytosolic NBD1 (nucleotide-binding domain 1); and (ii) in the presence of corrector drug VX-809, which rescues cell-surface expression of a range of disease-causing CFTR mutants. Both lead to increased shielding of the CFTR N-terminus, and their additivity implies different modes of action. Early assembly of NBD1 and TMD1 is essential for CFTR folding and positions both domains for the required assembly with TMD2. Altogether, we have gained insights into this first, nucleating, VX-809-enhanced domain-assembly event during and immediately after CFTR translation, involving structures conserved in type-I ABC exporters.
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Affiliation(s)
- Bertrand Kleizen
- Cellular Protein Chemistry, Bijvoet Centre for Biomolecular Research, Science for Life, Faculty of Science, Utrecht University, Utrecht, the Netherlands
| | - Marcel van Willigen
- Cellular Protein Chemistry, Bijvoet Centre for Biomolecular Research, Science for Life, Faculty of Science, Utrecht University, Utrecht, the Netherlands; Julius Clinical Ltd, Broederplein 41-43, 3703 CD Zeist, the Netherlands(‡)
| | - Marjolein Mijnders
- Cellular Protein Chemistry, Bijvoet Centre for Biomolecular Research, Science for Life, Faculty of Science, Utrecht University, Utrecht, the Netherlands; Division of Pediatrics, Wilhelmina Children's Hospital, University Medical Center Utrecht, Utrecht, the Netherlands‡
| | - Florence Peters
- Cellular Protein Chemistry, Bijvoet Centre for Biomolecular Research, Science for Life, Faculty of Science, Utrecht University, Utrecht, the Netherlands
| | - Magda Grudniewska
- Cellular Protein Chemistry, Bijvoet Centre for Biomolecular Research, Science for Life, Faculty of Science, Utrecht University, Utrecht, the Netherlands; GenomeScan B.V, Plesmanlaan 1d, 2333 BZ Leiden, the Netherlands‡
| | - Tamara Hillenaar
- Cellular Protein Chemistry, Bijvoet Centre for Biomolecular Research, Science for Life, Faculty of Science, Utrecht University, Utrecht, the Netherlands
| | - Ann Thomas
- Cellular Protein Chemistry, Bijvoet Centre for Biomolecular Research, Science for Life, Faculty of Science, Utrecht University, Utrecht, the Netherlands; UniQure, Paasheuvelweg 25a, 1105 BP Amsterdam, the Netherlands‡
| | - Laurens Kooijman
- Cellular Protein Chemistry, Bijvoet Centre for Biomolecular Research, Science for Life, Faculty of Science, Utrecht University, Utrecht, the Netherlands; Department of Chemistry, University of Zurich, Winterthurerstrasse 190, 8057 Zürich, Switzerland‡
| | - Kathryn W Peters
- Departments of Pediatrics and Cell Biology, School of Medicine, University of Pittsburgh, Pittsburgh, PA 15261, USA
| | - Raymond Frizzell
- Departments of Pediatrics and Cell Biology, School of Medicine, University of Pittsburgh, Pittsburgh, PA 15261, USA
| | - Peter van der Sluijs
- Cellular Protein Chemistry, Bijvoet Centre for Biomolecular Research, Science for Life, Faculty of Science, Utrecht University, Utrecht, the Netherlands
| | - Ineke Braakman
- Cellular Protein Chemistry, Bijvoet Centre for Biomolecular Research, Science for Life, Faculty of Science, Utrecht University, Utrecht, the Netherlands.
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Cai Z, Scott-Ward TS, Sheppard DN. Voltage-dependent gating of the cystic fibrosis transmembrane conductance regulator Cl- channel. J Gen Physiol 2003; 122:605-20. [PMID: 14581585 PMCID: PMC2229579 DOI: 10.1085/jgp.200308921] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2003] [Accepted: 10/02/2003] [Indexed: 11/30/2022] Open
Abstract
When excised inside-out membrane patches are bathed in symmetrical Cl--rich solutions, the current-voltage (I-V) relationship of macroscopic cystic fibrosis transmembrane conductance regulator (CFTR) Cl- currents inwardly rectifies at large positive voltages. To investigate the mechanism of inward rectification, we studied CFTR Cl- channels in excised inside-out membrane patches from cells expressing wild-type human and murine CFTR using voltage-ramp and -step protocols. Using a voltage-ramp protocol, the magnitude of human CFTR Cl- current at +100 mV was 74 +/- 2% (n = 10) of that at -100 mV. This rectification of macroscopic CFTR Cl- current was reproduced in full by ensemble currents generated by averaging single-channel currents elicited by an identical voltage-ramp protocol. However, using a voltage-step protocol the single-channel current amplitude (i) of human CFTR at +100 mV was 88 +/- 2% (n = 10) of that at -100 mV. Based on these data, we hypothesized that voltage might alter the gating behavior of human CFTR. Using linear three-state kinetic schemes, we demonstrated that voltage has marked effects on channel gating. Membrane depolarization decreased both the duration of bursts and the interburst interval, but increased the duration of gaps within bursts. However, because the voltage dependencies of the different rate constants were in opposite directions, voltage was without large effect on the open probability (Po) of human CFTR. In contrast, the Po of murine CFTR was decreased markedly at positive voltages, suggesting that the rectification of murine CFTR is stronger than that of human CFTR. We conclude that inward rectification of CFTR is caused by a reduction in i and changes in gating kinetics. We suggest that inward rectification is an intrinsic property of the CFTR Cl- channel and not the result of pore block.
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Affiliation(s)
- Zhiwei Cai
- Department of Physiology, School of Medical Sciences, University Walk, University of Bristol, Bristol BS8 1TD, UK.
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