Structure of a Bacterial ABC Transporter Involved in the Import of an Acidic Polysaccharide Alginate.
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Maruyama Y, Itoh T, Kaneko A, Nishitani Y, Mikami B, Hashimoto W, Murata K
Structure of a Bacterial ABC Transporter Involved in the Import of an Acidic Polysaccharide Alginate.
Structure. 2015 Sep 1;23(9):1643-54. doi: 10.1016/j.str.2015.06.021. Epub 2015 Jul 30.
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- 26235029 [ View in PubMed]
- Abstract
The acidic polysaccharide alginate represents a promising marine biomass for the microbial production of biofuels, although the molecular and structural characteristics of alginate transporters remain to be clarified. In Sphingomonas sp. A1, the ATP-binding cassette transporter AlgM1M2SS is responsible for the import of alginate across the cytoplasmic membrane. Here, we present the substrate-transport characteristics and quaternary structure of AlgM1M2SS. The addition of poly- or oligoalginate enhanced the ATPase activity of reconstituted AlgM1M2SS coupled with one of the periplasmic solute-binding proteins, AlgQ1 or AlgQ2. External fluorescence-labeled oligoalginates were specifically imported into AlgM1M2SS-containing proteoliposomes in the presence of AlgQ2, ATP, and Mg(2+). The crystal structure of AlgQ2-bound AlgM1M2SS adopts an inward-facing conformation. The interaction between AlgQ2 and AlgM1M2SS induces the formation of an alginate-binding tunnel-like structure accessible to the solvent. The translocation route inside the transmembrane domains contains charged residues suitable for the import of acidic saccharides.