Distorted octahedral coordination of tungstate in a subfamily of specific binding proteins |
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Authors: | Kaspar Hollenstein Mireia Comellas-Bigler Loes E Bevers Martin C Feiters Wolfram Meyer-Klaucke Peter-Leon Hagedoorn Kaspar P Locher |
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Institution: | 1. Institute of Molecular Biology and Biophysics, ETH Zurich, Schafmattstrasse 20, 8093, Zurich, Switzerland 2. Department of Biotechnology, Delft University of Technology, Julianalaan 67, 2628 BC, Delft, The Netherlands 3. Department of Organic Chemistry, Faculty of Science, Institute for Molecules and Materials, Radboud University Nijmegen, Heyendaalseweg 135, 6525 AJ, Nijmegen, The Netherlands 4. European Molecular Biology Laboratory, Hamburg Unit, c/o Deutsches Elektronen Synchrotron, Notkestra?e 85, 22607, Hamburg, Germany
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Abstract: | Bacteria and archaea import molybdenum and tungsten from the environment in the form of the oxyanions molybdate (MoO4
2−) and tungstate (WO4
2−). These substrates are captured by an external, high-affinity binding protein, and delivered to ATP binding cassette transporters,
which move them across the cell membrane. We have recently reported a crystal structure of the molybdate/tungstate binding
protein ModA/WtpA from Archaeoglobus fulgidus, which revealed an octahedrally coordinated central metal atom. By contrast, the previously determined structures of three
bacterial homologs showed tetracoordinate molybdenum and tungsten atoms in their binding pockets. Until then, coordination
numbers above four had only been found for molybdenum/tungsten in metalloenzymes where these metal atoms are part of the catalytic
cofactors and coordinated by mostly non-oxygen ligands. We now report a high-resolution structure of A. fulgidus ModA/WtpA, as well as crystal structures of four additional homologs, all bound to tungstate. These crystal structures match
X-ray absorption spectroscopy measurements from soluble, tungstate-bound protein, and reveal the details of the distorted
octahedral coordination. Our results demonstrate that the distorted octahedral geometry is not an exclusive feature of the
A. fulgidus protein, and suggest distinct binding modes of the binding proteins from archaea and bacteria.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.
K. Hollenstein and M. Comellas-Bigler contributed equally to this work. |
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Keywords: | Tungsten Binding proteins Octahedral coordination Crystal structure Extended X-ray absorption fine structure |
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