1l5v

From Proteopedia

---

Revision as of 18:10, 20 November 2007

proteopedia linkproteopedia link

spinqualitylabelsall models 1l5v, resolution 2.0Å Show:Asymmetric Unit Biological Assembly Drag the structure with the mouse to rotate   Export Animated Image

Crystal Structure of the Maltodextrin Phosphorylase complexed with Glucose-1-phosphate

Overview

The bacterial enzyme maltodextrin phosphorylase (MalP) catalyses the, phosphorolysis of an alpha-1,4-glycosidic bond in maltodextrins, removing, the non-reducing glucosyl residues of linear oligosaccharides as, glucose-1-phosphate (Glc1P). In contrast to the well-studied muscle, glycogen phosphorylase (GP), MalP exhibits no allosteric properties and, has a higher affinity for linear oligosaccharides than GP. We have used, MalP as a model system to study catalysis in the crystal in the direction, of maltodextrin synthesis. The 2.0A crystal structure of the MalP/Glc1P, binary complex shows that the Glc1P substrate adopts a conformation seen, previously with both inactive and active forms of mammalian GP, with the, phosphate group not in close contact with the 5'-phosphate group of the, essential pyridoxal phosphate (PLP) cofactor. In the active MalP enzyme, the residue Arg569 stabilizes the negative-charged Glc1P, whereas in the, inactive form of GP this key residue is held away from the catalytic site, by loop 280s and an allosteric transition of the mammalian enzyme is, required for activation. The comparison between MalP structures shows that, His377, through a hydrogen bond with the 6-hydroxyl group of Glc1P, substrate, triggers a conformational change of the 380s loop. This mobile, region folds over the catalytic site and contributes to the specific, recognition of the oligosaccharide and to the synergism between substrates, in promoting the formation of the MalP ternary complex. The structures, solved after the diffusion of oligosaccharides (either maltotetraose, G4, or maltopentaose, G5) into MalP/Glc1P crystals show the formation of, phosphate and elongation of the oligosaccharide chain. These structures, refined at 1.8A and at 2.2A, confirm that only when an oligosaccharide is, bound to the catalytic site will Glc1P bend its phosphate group down so it, can contact the PLP 5' phosphate group and promote catalysis. The, relatively large oligosaccharide substrates can diffuse quickly into the, MalP/Glc1P crystals and the enzymatic reaction can occur without, significant crystal damage. These structures obtained before and after, catalysis have been used as frames of a molecular movie. This movie, reveals the relative positions of substrates in the catalytic channel and, shows a minimal movement of the protein, involving mainly Arg569, which, tracks the substrate phosphate group.

About this Structure

1L5V is a Single protein structure of sequence from Escherichia coli with G1P, TRS and PLP as ligands. Active as Phosphorylase, with EC number 2.4.1.1 Full crystallographic information is available from OCA.

Reference

Enzymatic catalysis in crystals of Escherichia coli maltodextrin phosphorylase., Geremia S, Campagnolo M, Schinzel R, Johnson LN, J Mol Biol. 2002 Sep 13;322(2):413-23. PMID:12217700

Page seeded by OCA on Tue Nov 20 20:17:41 2007