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A Novel Saturation Mutagenesis Approach: Single Step Characterization of Regulatory Protein Binding Sites in RNA Using Phosphorothioates
Published on: August 21, 2018
Characterization of vanadium-binding sites of the vanadium-binding protein Vanabin2 by site-directed mutagenesis
Tatsuya Ueki1, Norifumi Kawakami, Masaaki Toshishige
1Molecular Physiology Laboratory, Department of Biological Science, Graduate School of Science, Hiroshima University, 1-3-1 Kagamiyama, Higashi-Hiroshima 739-8526, Japan. ueki@hiroshima-u.ac.jp
Background:
Vanabins are a unique protein family of vanadium-binding proteins with nine disulfide bonds. Possible binding sites for VO2+ in Vanabin2 from a vanadium-rich ascidian Ascidia sydneiensis samea have been detected by nuclear magnetic resonance study, but the metal selectivity and metal-binding ability of each site was not examined.
Methods:
In order to reveal functional contribution of each binding site, we prepared several mutants of Vanabin2 by in vitro site-directed mutagenesis and analyzed their metal selectivity and affinity by immobilized metal-ion affinity chromatography and Hummel Dreyer method.
Results:
Mutation at K10/R60 (site 1) markedly reduced the affinity for VO2+. Mutation at K24/K38/R41/R42 (site 2) decreased the maximum binding number, but only slightly increased the overall affinity for VO2+. Secondary structure of both mutants was the same as that of the wild type as assessed by circular dichroism spectroscopy. Mutation in disulfide bonds near the site 1 did not affect its high affinity binding capacity, while those near the site 2 decreased the overall affinity for VO2+.
General Significance:
These results suggested that the site 1 is a high affinity binding site for VO2+, while the site 2 composes a moderate affinity site for multiple VO2+.
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