d-Cysteine Ligands Control Metal Geometries within De Novo Designed Three-Stranded Coiled Coils
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Author list: Ruckthong L., Peacock A.F.A., Pascoe C.E., Hemmingsen L., Stuckey J.A., Pecoraro V.L.
Publisher: Wiley
Publication year: 2017
Journal: Chemistry - A European Journal (0947-6539)
Volume number: 23
Issue number: 34
Start page: 8232
End page: 8243
Number of pages: 12
ISSN: 0947-6539
eISSN: 1521-3765
Languages: English-Great Britain (EN-GB)
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Abstract
Although metal ion binding to naturally occurring l-amino acid proteins is well documented, understanding the impact of the opposite chirality (d-)amino acids on the structure and stereochemistry of metals is in its infancy. We examine the effect of a d-configuration cysteine within a designed l-amino acid three-stranded coiled coil in order to enforce a precise coordination number on a metal center. The d chirality does not alter the native fold, but the side-chain re-orientation modifies the sterics of the metal binding pocket. l-Cys side chains within the coiled-coil structure have previously been shown to rotate substantially from their preferred positions in the apo structure to create a binding site for a tetra-coordinate metal ion. However, here we show by X-ray crystallography that d-Cys side chains are preorganized within a suitable geometry to bind such a ligand. This is confirmed by comparison of the structure of ZnIICl(CSL16DC)3 2− to the published structure of ZnII(H2O)(GRAND-CSL12AL16LC)3 −. Moreover, spectroscopic analysis indicates that the CdII geometry observed by using l-Cys ligands (a mixture of three- and four-coordinate CdII) is altered to a single four-coordinate species when d-Cys is present. This work opens a new avenue for the control of the metal site environment in man-made proteins, by simply altering the binding ligand with its mirror-imaged d configuration. Thus, the use of non-coded amino acids in the coordination sphere of a metal promises to be a powerful tool for controlling the properties of future metalloproteins. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Keywords
d-amino acids, protein design, X-ray Crystallography
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