期刊
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
卷 106, 期 14, 页码 5563-5568出版社
NATL ACAD SCIENCES
DOI: 10.1073/pnas.0811322106
关键词
crystal; molecular dynamics simulation; neurotransmitter:sodium symport; second substrate (S2)-binding site; scintillation proximity binding assay
资金
- National Institutes of Health [DA022413, DA017293, DA023694, DA012408]
- Novo Nordisk Foundaton
- Lundbeck Foundation
- Danish National Research Foundation
- Lundbeck Foundation [R34-2011-3868] Funding Source: researchfish
The first crystal structure of the neurotransmitter/sodium symporter homolog LeuT revealed an occluded binding pocket containing leucine and 2 Na+; later structures showed tricyclic antidepressants (TCAs) in an extracellular vestibule approximate to 11 angstrom above the bound leucine and 2 Na+. We recently found this region to be a second binding (S2) site and that binding of substrate to this site triggers Na+-coupled substrate symport. Here, we show a profound inhibitory effect of n-octyl-beta-D-glucopyranoside (OG), the detergent used for LeuT crystallization, on substrate binding to the S2 site. In parallel, we determined at 2.8 angstrom the structure of LeuT-E290S, a mutant that, like LeuT-WT, binds 2 substrate molecules. This structure was similar to that of WT and clearly revealed an OG molecule in the S2 site. We also observed electron density at the S2 site in LeuT-WT crystals, and this also was accounted for by an OG molecule in that site. Computational analyses, based on the available crystal structures of LeuT, indicated the nature of structural arrangements in the extracellular region of LeuT that differentiate the actions of substrates from inhibitors bound in the S2 site. We conclude that the current LeuT crystal structures, all of which have been solved in OG, represent functionally blocked forms of the transporter, whereas a substrate bound in the S2 site ill promote a different state that is essential for Na+-coupled symport.
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