Crystal structure of alginate lyase A1-III complexed with trisaccharide product at 2.0 Å resolution

The structure of Al-III from a Sphingonronas species Al complexed with trisaccharide product (4-deoxy-L-erythro-hex-4-enepyranosyluronate-mannuronate-mannuronic acid) was determined by X-ray crystallography at 2.0 Angstrom with an R-factor of 0.16. The final model of the complex form comprising 351 amino acid residues, 245 water molecules, one sulfate ion and one trisaccharide product exhibited a C-alpha r.m.s.d. value of 0.154 Angstrom with the reported apo form of the enzyme. The trisaccharide was bound in the active cleft at subsites -3 similar to - 1 from the non-reducing end by forming several hydrogen bonds and van der Waals interactions with protein atoms. The catalytic residue was estimated to be Tyr246, which existed between subsites -1 and +1 based on a mannuronic acid model oriented at subsite +1. (C) 2001 Academic Press.