Book of Abstracts: Albany 2003
June 17-21 2003
Interaction of a breast cancer growth inhibiting cyclopeptide with the G-protein-coupled receptor model GPR30
The procedure of molecular dynamics simulated annealing is applied to locate a probable receptor and binding site of a cyclocpeptide which inhibits estrogen-stimulated proliferation of breast cancer. The hydrophilic cyclopeptide EMTOVNOGQ (O = 4-hydroxyproline), derived from alpha-fetoprotein, is an inhibitor of estrogen-stimulated proliferation of human breast cancer. This peptide has been shown to act through a mechanism different from that of estrogen; however, its receptor is unknown. We report computer experiments that suggest that this peptide may execute its actions by interacting with GPR30, a G-protein-coupled receptor. The subject of this work is the simulation, by molecular dynamics simulated annealing, of the interaction of cyclopeptide EMTOVNOGQ with receptor GPR30 protein. A conformational analysis of the cyclopeptide was undertaken and the final structure was docked on several sites of the GPR30 3D model. Our results show that the cyclopeptide interacts on the pocket located between TM6 and TM7 transmembrane helices of the G-protein, triggering a slight conformational change in the secondary structure of the receptor in the complex.
The diagram shows the cyclopeptide (the green sticks) into the binding site of the GPR30 protein. DELPHI calculations of the electrostatic potential over the Connolly surface of the GPR30 receptor reveal a number of differences in the distribution of positive and negative regions. The binding site appears as a pocket with two large bays, one positive and one negative. Electrostatic surface potential contoured from ?3 (red) to +3 (blue) kT/e (± 0.077 volt). The figure was made using InsightII and DELPHI programs.
Based on differences in accessible surface areas between GPR30 and its ligand, the residues in the interaction zone were identified. The cyclopeptide is stabilized in the active site by forming a network of hydrogen bonds between Glu, Thr, 1Pro(OH) and GLn residues of the ligand and Arg-259, Cys-271, Asn-316, Asn-320 and Tyr-324 of the G-protein.
Overview of the final model of the cyclopeptide ligand/ GPR30 receptor complex. The Connolly surface (blue) was also displayed on the binding pocket of the GPR30 receptor. Hydrogen bonds between the residues of the GPR30 protein and the cyclopeptide were displayed in dashed lines.
Moreover, the study of the electrostatic surface potential on the GPR30 receptor shows that the active site is more positively charged than the other sites. Our modeling indicate a plausible interaction of the cyclopeptide with the seven transmembrane GPR30 protein. This may have profound implications for the treatment of breast cancer.
The authors thank Professor Gerrit Vriend, University of Nijmegen, Faculty of science, Nijmegen, The Netherlands, for giving permission to use the 3D model of GPR30 protein described in the GPCR database: http://www.gpcr.org/7tm/. We also thank World Health Organization of the UN for a fellowship to one of us (AH). We thank J. A. Bennett, H. I. Jacobson, and T. Andersen, of Albany Medical College for bringing attention to the cyclopeptide in this study.