3. Results and Discussion
Docking of small molecule compounds into the binding site of a receptor and estimating the binding affinity of
the complex is an important part of the structure based drug design process. AutoDock Vina is a open-source
program for drug discovery, molecular docking and virtual screening, offering multicore capability, high
performance and enhanced accuracy and ease tof use. The parameters chosen for the docking can be judged by the
docking tool’s ability to reproduce the binding mode of a ligand to protein, when the structure of the ligand–protein
complex is known. The criterion usually used is the all atom root mean square deviation (RMSD) between the
docked position and the crystallographically observed binding position of the ligand, and success is typically
regarded as being less than 2Å9
.
In this study, the native ligand was CP320626 (5-chloro-1H-indole-2-carboxylic acid [1-(4-fluorbenzyl)-2-(4-
hydroxypiperidin-1yl)-2-oxoethyl] amide). This compound has been identified as a potent inhibitor of human liver
glycogen phosphorylase. CP320626 is also a potent inhibitor of human muscle glycogen phosphorylase.
Oikonomakos et al. elucidated the structural basis of the inhibition mechanism of CP320626, by determination the
complex of rabbit muscle glycogen phosphorylase with CP3206261
. Figure 2 showed the model of interaction
between CP320626 and binding site of glycogen phosphorylase. Amino acids residues of glycogen phosphorylase
which involved in interaction with CP320626 were Glu190A, Arg60A and Lys191A. A hydrogen bond was occured
between carbonyl group of Glu190A as hydrogen bond acceptor and –NH of indole ring as hydrogen bond donor.
Between cationic center of Arg60A and anionic center of CP320626, an electrostatic interaction was formed.
Prathipati et al. reported that the mayor interaction between CP320626 and the enzyme are hydrophobic interactions
between the indole-aromatic ring and hydrophobic residues such as Pro229, Trp189, and Trp67 which is represented
by a hydrophobic feature on the indole-ring1
.