Structure and function of complex of substrate-binding protein and macromolecule-specific ABC transpoter

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The structure and function relationship of macromolecule(alginate)-specific ABC transporter (importer:AlgM1-AlgM2/AlgS-AlgS) of Sphingomonas sp, A1 was analyzed.The substrate-binding proteins (AlgQ) bind/reliese alginate by opening/closing the N-domein and C-domein. The subsite 1 in the AlgQ specifically binds mannuronate. Through the contact with alginate-bound AlgQ, the permeases (AlgM1 and AlgM2) constituting importer open, receive alginate from AlgQ, and then alginate is introduced into cytosol by using ATP-hydrolyzing energy, which is generated by the action of AlgS (ATPase). This ATP transporter was different from the ABC transporters responsible for the transport of low-molecular weight substrates in that the substrate-binding protein (AlgQ) forms the tunnel that allows the passage of alginate, a long chain acid polysaccharide.