Oligosaccharide conformation and protein saccharide interactions in solution

The interaction between glycogen and the enzyme phosphorylase has been determined by x-ray diffraction of the protein, complexed to a low-molecular weight analogue of an A-chain of glycogen, maltoheptaose. All of the glucans of the saccharide are observed, even though only four of the residues are in direct contact with the enzyme. The saccharide has a helical secondary structure arising from an 02-03’ hydrogen bonding interaction. The saccharide helix binds in a shallow groove between two α-helices at the protein surface in small subdomainof 56 amino acids. This subdomain has an unusual βα3β2structure.The protein contacts include hydrogen bonding, hydrogen bond network formation, burial of protein salt bridges, and van der Waals interactions.