1abb

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spinqualitylabelsall models 1abb, resolution 2.8Å Show:Asymmetric Unit Biological Assembly Drag the structure with the mouse to rotate   Export Animated Image

CONTROL OF PHOSPHORYLASE B CONFORMATION BY A MODIFIED COFACTOR: CRYSTALLOGRAPHIC STUDIES ON R-STATE GLYCOGEN PHOSPHORYLASE RECONSTITUTED WITH PYRIDOXAL 5'-DIPHOSPHATE

Overview

Previous crystallographic studies on glycogen phosphorylase have described, the different conformational states of the protein (T and R) that, represent the allosteric transition and have shown how the properties of, the 5'-phosphate group of the cofactor pyridoxal phosphate are influenced, by these conformational states. The present work reports a study on, glycogen phosphorylase b (GPb) complexed with a modified cofactor, pyridoxal 5'-diphosphate (PLPP), in place of the natural cofactor., Solution studies (Withers, S.G., Madsen, N.B., & Sykes, B.D., 1982, Biochemistry 21, 6716-6722) have shown that PLPP promotes R-state, properties of the enzyme indicating that the cofactor can influence the, conformational state of the protein. GPb complexed with pyridoxal, 5'-diphosphate (PLPP) has been crystallized in the presence of IMP and, ammonium sulfate in the monoclinic R-state crystal form and the structure, refined from X-ray data to 2.8 A resolution to a crystallographic R value, of 0.21. The global tertiary and quaternary structure in the vicinity of, the Ser 14 and the IMP sites are nearly identical to those observed for, the R-state GPb-AMP complex. At the catalytic site the second phosphate of, PLPP is accommodated with essentially no change in structure from the, R-state structure and is involved in interactions with the side chains of, two lysine residues (Lys 568 and Lys 574) and the main chain nitrogen of, Arg 569. Superposition of the T-state structure shows that were the PLPP, to be incorporated into the T-state structure there would be a close, contact with the 280s loop (residues 282-285) that would encourage the T, to R allosteric transition. The second phosphate of the PLPP occupies a, site that is distinct from other dianionic binding sites that have been, observed for glucose-1-phosphate and sulfate (in the R state) and for, heptulose-2-phosphate (in the T state). The results indicate mobility in, the dianion recognition site, and the precise position is dependent on, other linkages to the dianion. In the modified cofactor the second, phosphate site is constrained by the covalent link to the first phosphate, of PLPP. The observed position in the crystal suggests that it is too far, from the substrate site to represent a site for catalysis.

About this Structure

1ABB is a Single protein structure of sequence from Oryctolagus cuniculus with SO4, PDP and IMP as ligands. Active as Phosphorylase, with EC number 2.4.1.1 Full crystallographic information is available from OCA.

Reference

Control of phosphorylase b conformation by a modified cofactor: crystallographic studies on R-state glycogen phosphorylase reconstituted with pyridoxal 5'-diphosphate., Leonidas DD, Oikonomakos NG, Papageorgiou AC, Acharya KR, Barford D, Johnson LN, Protein Sci. 1992 Sep;1(9):1112-22. PMID:1304390

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