The X-ray Crystallographic Structure ofEscherichia coli Branching Enzyme

• Published in: The Journal of biological chemistry Vol. 277; no. 44; pp. 42164 - 42170
• Main Authors: Marta C. Abad, Kim Binderup, Jorge Rios-Steiner, Raghuvir K. Arni, Jack Preiss, James H. Geiger
• Format: Journal Article
• Language: English
• Published: American Society for Biochemistry and Molecular Biology 01.11.2002
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M205746200

Branching enzyme catalyzes the formation of α-1,6 branch points in either glycogen or starch. We report the 2.3-Å crystal structure of glycogen branching enzyme from Escherichia coli . The enzyme consists of three major domains, an NH 2 -terminal seven-stranded β-sandwich domain, a COOH-terminal domain, and a central α/β-barrel domain containing the enzyme active site. While the central domain is similar to that of all the other amylase family enzymes, branching enzyme shares the structure of all three domains only with isoamylase. Oligosaccharide binding was modeled for branching enzyme using the enzyme-oligosaccharide complex structures of various α-amylases and cyclodextrin glucanotransferase and residues were implicated in oligosaccharide binding. While most of the oligosaccharides modeled well in the branching enzyme structure, an approximate 50° rotation between two of the glucose units was required to avoid steric clashes with Trp 298 of branching enzyme. A similar rotation was observed in the mammalian α-amylase structure caused by an equivalent tryptophan residue in this structure. It appears that there are two binding modes for oligosaccharides in these structures depending on the identity and location of this aromatic residue.