Location of Pyridoxal Phosphate in Glycogen Phosphorylase a

• Published in: Proceedings of the National Academy of Sciences - PNAS 1977-11, Vol.74 (11), p.4757-4761
• Main Authors: Sygusch, J., Madsen, N. B., Kasvinsky, P. J., Fletterick, R. J.
• Format: Article
• Language: English
• Subjects: Amino acids; Binding Sites; Biochemistry; Chemical Phenomena; Chemistry; Coenzymes; Crystals; Electron density; Enzymes; Glycogen; Ligands; Models, Molecular; Phosphates; Phosphites; Phosphorylases; Pyridoxal Phosphate - analysis; X-Ray Diffraction
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.74.11.4757

The pyridoxal 5′-phosphate cofactor of glycogen phosphorylase a (1,4-α -D-glucan:orthophosphate α -glucosyltransferase, EC 2.4.1.1) has been positioned on the protomer with x-ray diffraction data, chemical markers, and sequence information. The electron density was computed from 3.0- angstrom resolution phases calculated from four heavy-atom derivatives. The cofactor is buried inside the protomer adjacent to the glucose-binding site. The phosphoryl substrates Piand glucose-1-P each bind at two sites on the protomer. At low concentrations, Piand glucose-1-P bind in the same location as does the allosteric effector AMP, near the monomer-monomer interface and some 30 angstrom from the glucose site. At high concentrations glucose-1-P also binds strongly at the glucose site, with its phosphate only 7.2 angstrom from that of the cofactor. Inorganic phosphate can also bind at this site. Implications for the participation of the pyridoxal phosphate in the catalytic mechanism are discussed in the light of these structural findings as well as the wealth of indirect evidence in the literature.