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Malinauskaite L, Said S, Sahin C, Grouleff J, Shahsavar A, Bjerregaard H, Noer P, Severinsen K, Boesen T, Schiøtt B, Sinning S, Nissen P. A conserved leucine occupies the empty substrate site of LeuT in the Na(+)-free return state. Nat Commun 2016; 7:11673. [PMID: 27221344 PMCID: PMC4894957 DOI: 10.1038/ncomms11673] [Citation(s) in RCA: 45] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2016] [Accepted: 04/18/2016] [Indexed: 02/05/2023] Open
Abstract
Bacterial members of the neurotransmitter:sodium symporter (NSS) family perform Na(+)-dependent amino-acid uptake and extrude H(+) in return. Previous NSS structures represent intermediates of Na(+)/substrate binding or intracellular release, but not the inward-to-outward return transition. Here we report crystal structures of Aquifex aeolicus LeuT in an outward-oriented, Na(+)- and substrate-free state likely to be H(+)-occluded. We find a remarkable rotation of the conserved Leu25 into the empty substrate-binding pocket and rearrangements of the empty Na(+) sites. Mutational studies of the equivalent Leu99 in the human serotonin transporter show a critical role of this residue on the transport rate. Molecular dynamics simulations show that extracellular Na(+) is blocked unless Leu25 is rotated out of the substrate-binding pocket. We propose that Leu25 facilitates the inward-to-outward transition by compensating a Na(+)- and substrate-free state and acts as the gatekeeper for Na(+) binding that prevents leak in inward-outward return transitions.
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Affiliation(s)
- Lina Malinauskaite
- Danish Research Institute of Translational Neuroscience-DANDRITE, Nordic-EMBL Partnership for Molecular Medicine, Department of Molecular Biology and Genetics, Aarhus University, Gustav Wieds Vej 10C, Aarhus C DK-8000, Denmark
| | - Saida Said
- Translational Neuropsychiatry Unit, Department of Clinical Medicine, Aarhus University, Skovagervej 2, Risskov DK-8240, Denmark
| | - Caglanur Sahin
- Danish Research Institute of Translational Neuroscience-DANDRITE, Nordic-EMBL Partnership for Molecular Medicine, Department of Molecular Biology and Genetics, Aarhus University, Gustav Wieds Vej 10C, Aarhus C DK-8000, Denmark
| | - Julie Grouleff
- inSPIN and iNANO centers, Department of Chemistry, Aarhus University, Langelandsgade 140, Aarhus C DK-8000, Denmark
| | - Azadeh Shahsavar
- Danish Research Institute of Translational Neuroscience-DANDRITE, Nordic-EMBL Partnership for Molecular Medicine, Department of Molecular Biology and Genetics, Aarhus University, Gustav Wieds Vej 10C, Aarhus C DK-8000, Denmark
| | - Henriette Bjerregaard
- Translational Neuropsychiatry Unit, Department of Clinical Medicine, Aarhus University, Skovagervej 2, Risskov DK-8240, Denmark
| | - Pernille Noer
- Translational Neuropsychiatry Unit, Department of Clinical Medicine, Aarhus University, Skovagervej 2, Risskov DK-8240, Denmark
| | - Kasper Severinsen
- Translational Neuropsychiatry Unit, Department of Clinical Medicine, Aarhus University, Skovagervej 2, Risskov DK-8240, Denmark
| | - Thomas Boesen
- Danish Research Institute of Translational Neuroscience-DANDRITE, Nordic-EMBL Partnership for Molecular Medicine, Department of Molecular Biology and Genetics, Aarhus University, Gustav Wieds Vej 10C, Aarhus C DK-8000, Denmark
| | - Birgit Schiøtt
- inSPIN and iNANO centers, Department of Chemistry, Aarhus University, Langelandsgade 140, Aarhus C DK-8000, Denmark
| | - Steffen Sinning
- Translational Neuropsychiatry Unit, Department of Clinical Medicine, Aarhus University, Skovagervej 2, Risskov DK-8240, Denmark
| | - Poul Nissen
- Danish Research Institute of Translational Neuroscience-DANDRITE, Nordic-EMBL Partnership for Molecular Medicine, Department of Molecular Biology and Genetics, Aarhus University, Gustav Wieds Vej 10C, Aarhus C DK-8000, Denmark
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Koldsø H, Noer P, Grouleff J, Autzen HE, Sinning S, Schiøtt B. Unbiased simulations reveal the inward-facing conformation of the human serotonin transporter and Na(+) ion release. PLoS Comput Biol 2011; 7:e1002246. [PMID: 22046120 PMCID: PMC3203053 DOI: 10.1371/journal.pcbi.1002246] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2011] [Accepted: 09/12/2011] [Indexed: 11/19/2022] Open
Abstract
Monoamine transporters are responsible for termination of synaptic signaling and are involved in depression, control of appetite, and anxiety amongst other neurological processes. Despite extensive efforts, the structures of the monoamine transporters and the transport mechanism of ions and substrates are still largely unknown. Structural knowledge of the human serotonin transporter (hSERT) is much awaited for understanding the mechanistic details of substrate translocation and binding of antidepressants and drugs of abuse. The publication of the crystal structure of the homologous leucine transporter has resulted in homology models of the monoamine transporters. Here we present extended molecular dynamics simulations of an experimentally supported homology model of hSERT with and without the natural substrate yielding a total of more than 1.5 µs of simulation of the protein dimer. The simulations reveal a transition of hSERT from an outward-facing occluded conformation to an inward-facing conformation in a one-substrate-bound state. Simulations with a second substrate in the proposed symport effector site did not lead to conformational changes associated with translocation. The central substrate binding site becomes fully exposed to the cytoplasm leaving both the Na+-ion in the Na2-site and the substrate in direct contact with the cytoplasm through water interactions. The simulations reveal how sodium is released and show indications of early events of substrate transport. The notion that ion dissociation from the Na2-site drives translocation is supported by experimental studies of a Na2-site mutant. Transmembrane helices (TMs) 1 and 6 are identified as the helices involved in the largest movements during transport. The human serotonin transporter belongs to the family of neurotransmitter transporters, which are located in the presynaptic nerve end, from where it is responsible for termination of synaptic serotonin signaling. Imbalance in serotonin concentration is related to various neuronal conditions such as depression, regulation of appetite etc. Very limited structural information of hSERT is available, but it is believed that the protein functions through an alternating access mechanism, where the central binding site is either exposed to the outside or the inside of the cell. We have previously published an experimentally validated outward-occluded homology model of hSERT, and here we reveal the inward-facing conformation of hSERT from molecular dynamics simulations, from which we can identify the main movements occurring during the translocation. From the inward-facing conformation we observe ion release, revealing important information on the sequence of events during transport. Following transport of the sodium ion, the substrate also shows early events of transport. The ion follows a cytoplasmic pathway as hinted at from experiments, and the ligand binding site becomes fully solvated by water through this same pathway. Experiments using an Asp437Asn mutant of hSERT confirm the prediction that Asp437 is a central residue in controlling ion transport.
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Affiliation(s)
- Heidi Koldsø
- Center for Insoluble Protein Structures (inSPIN) and Interdisciplinary Nanoscience Center (iNANO), Department of Chemistry, Aarhus University, Aarhus, Denmark
| | - Pernille Noer
- Laboratory of Molecular Neurobiology, Centre for Psychiatric Research, Aarhus University Hospital, Risskov, Denmark
| | - Julie Grouleff
- Center for Insoluble Protein Structures (inSPIN) and Interdisciplinary Nanoscience Center (iNANO), Department of Chemistry, Aarhus University, Aarhus, Denmark
| | - Henriette Elisabeth Autzen
- Center for Insoluble Protein Structures (inSPIN) and Interdisciplinary Nanoscience Center (iNANO), Department of Chemistry, Aarhus University, Aarhus, Denmark
| | - Steffen Sinning
- Laboratory of Molecular Neurobiology, Centre for Psychiatric Research, Aarhus University Hospital, Risskov, Denmark
| | - Birgit Schiøtt
- Center for Insoluble Protein Structures (inSPIN) and Interdisciplinary Nanoscience Center (iNANO), Department of Chemistry, Aarhus University, Aarhus, Denmark
- * E-mail:
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Jensen OC, Stage S, Noer P. Classification and coding of commercial fishing injuries by work processes: an experience in the Danish fresh market fishing industry. Am J Ind Med 2005; 47:528-37. [PMID: 15898090 DOI: 10.1002/ajim.20163] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
BACKGROUND Work-related injuries in commercial fishing are of concern internationally. To better identify the causes of injury, this study coded occupational injuries by working processes in commercial fishing for fresh market fish. METHODS A classification system of the work processes was developed by participation in fishing vessel trips where observations and video recordings of the work operations on board were collected. Subsequently the system was pilot tested using the Danish Maritime Authority injury reports. RESULTS The developed classification system contains 17 main categories and up to 13 sub-categories of the work processes for each of the five different types of fishing. A total of 620 injury reports were reviewed and coded. Five percent (n = 33) of these were fatal injuries. The working processes were identified and coded according to the developed classification system for 553 (89%) injury reports: Danish seiner (n = 83), gill-netter (n = 122), beam trawler (n = 71), twin-trawler 2-T (n = 96), single/pair trawler 1-T (n = 181). Sixty-seven (11%) of the reports were unclassifiable due to lack of information. Preparing, shooting, and hauling of the gear and nets accounted for 50% of the injuries; they were most serious type of injuries such as fractures and sprains. Walking about the ship, in particular embarking and disembarking, climbing and descending ladders accounted for nearly one-fifth of the injuries. CONCLUSION We found that the working processes related to working with the gear and nets vary greatly in the different fishing methods. Coding of the injuries to the specific working processes allows for targeted prevention efforts.
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Affiliation(s)
- O C Jensen
- Research Unit of Maritime Medicine, University of Southern Denmark, Denmark.
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