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  • Title: The role of calcium binding to the EF-hand-like motif in bacterial solute-binding protein for alginate import.
    Author: Okumura K, Maruyama Y, Takase R, Mikami B, Murata K, Hashimoto W.
    Journal: Biosci Biotechnol Biochem; 2021 Nov 24; 85(12):2410-2419. PubMed ID: 34610097.
    Abstract:
    Gram-negative Sphingomonas sp. A1 incorporates acidic polysaccharide alginate into the cytoplasm via a cell-surface alginate-binding protein (AlgQ2)-dependent ATP-binding cassette transporter (AlgM1M2SS). We investigated the function of calcium bound to the EF-hand-like motif in AlgQ2 by introducing mutations at the calcium-binding site. The X-ray crystallography of the AlgQ2 mutant (D179A/E180A) demonstrated the absence of calcium binding and significant disorder of the EF-hand-like motif. Distinct from the wild-type AlgQ2, the mutant was quite unstable at temperature of strain A1 growth, although unsaturated alginate oligosaccharides stabilized the mutant by formation of substrate/protein complex. In the assay of ATPase and alginate transport by AlgM1M2SS reconstructed in the liposome, the wild-type and mutant AlgQ2 induced AlgM1M2SS ATPase activity in the presence of unsaturated alginate tetrasaccharide. These results indicate that the calcium bound to EF-hand-like motif stabilizes the substrate-unbound AlgQ2 but is not required for the complexation of substrate-bound AlgQ2 and AlgM1M2SS.
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