Journal
STRUCTURE
Volume 23, Issue 9, Pages 1643-1654Publisher
CELL PRESS
DOI: 10.1016/j.str.2015.06.021
Keywords
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Funding
- Japanese Society for the Promotion of Science
- Ministry of Education, Culture, Sports, Science, and Technology in Japan
- Grants-in-Aid for Scientific Research [15H04629, 26660062] Funding Source: KAKEN
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The acidic polysaccharide alginate represents a promising marine biomass for the microbial production of biofuels, although themolecular 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 Mg2+. 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.
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