2h39

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spinqualitylabelsall models 2h39, resolution 2.230Å Show:Asymmetric Unit Biological Assembly Drag the structure with the mouse to rotate   Export Animated Image

Crystal Structure of an ADP-Glucose Phosphorylase from Arabidopsis thaliana with bound ADP-Glucose

Overview

The X-ray crystal structure of the At5g18200.1 protein has been determined, to a nominal resolution of 2.30 A. The structure has a histidine triad, (HIT)-like fold containing two distinct HIT-like motifs. The sequence of, At5g18200.1 indicates a distant family relationship to the Escherichia, coli galactose-1-P uridylyltransferase (GalT): the determined structure of, the At5g18200.1 protein confirms this relationship. The At5g18200.1, protein does not demonstrate GalT activity but instead catalyzes adenylyl, transfer in the reaction of ADP-glucose with various phosphates. The best, acceptor among those evaluated is phosphate itself; thus, the At5g18200.1, enzyme appears to be an ADP-glucose phosphorylase. The enzyme catalyzes, the exchange of (14)C between ADP-[(14)C]glucose and glucose-1-P in the, absence of phosphate. The steady state kinetics of exchange follows the, ping-pong bi-bi kinetic mechanism, with a k(cat) of 4.1 s(-)(1) and K(m), values of 1.4 and 83 microM for ADP-[(14)C]glucose and glucose-1-P, respectively, at pH 8.5 and 25 degrees C. The overall reaction of, ADP-glucose with phosphate to produce ADP and glucose-1-P follows, ping-pong bi-bi steady state kinetics, with a k(cat) of 2.7 s(-)(1) and, K(m) values of 6.9 and 90 microM for ADP-glucose and phosphate, respectively, at pH 8.5 and 25 degrees C. The kinetics are consistent with, a double-displacement mechanism that involves a covalent adenylyl-enzyme, intermediate. The X-ray crystal structure of this intermediate was, determined to 1.83 A resolution and shows the AMP group bonded to, His(186). The value of K(eq) in the direction of ADP and glucose-1-P, formation is 5.0 at pH 7.0 and 25 degrees C in the absence of a divalent, metal ion, and it is 40 in the presence of 1 mM MgCl(2).

About this Structure

2H39 is a Single protein structure of sequence from Arabidopsis thaliana with ZN, CL and ADQ as ligands. This structure superseeds the now removed PDB entry 2GDK. Active as UDP-glucose--hexose-1-phosphate uridylyltransferase, with EC number 2.7.7.12 Full crystallographic information is available from OCA.

Reference

Structure and mechanism of an ADP-glucose phosphorylase from Arabidopsis thaliana., McCoy JG, Arabshahi A, Bitto E, Bingman CA, Ruzicka FJ, Frey PA, Phillips GN Jr, Biochemistry. 2006 Mar 14;45(10):3154-62. PMID:16519510

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