Solute-binding protein that binds D-mannuronate and D-taluronate (in vitro) (PubMed:25540822). Probably part of a tripartite ATP-independent periplasmic (TRAP) transport system that mediates solute transport into the cytoplasm. The complex is comprised of an extracytoplasmic solute-binding protein and a heteromeric permease formed by two transmembrane proteins. Belongs to the bacterial solute-binding protein 7 family.