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Structural basis of RasGRP binding to high-affinity PKC ligands
Suo-Bao Rong1, Istvan J Enyedy, Lixin Qiao
1Drug Discovery Program, Department of Neurology, Georgetown University Medical Center, 3970 Reservoir Road, Washington, D.C. 20007, USA.
Journal of Medicinal Chemistry
|February 8, 2002
Summary
Ras guanyl releasing protein (RasGRP) acts as a novel phorbol ester receptor. This study reveals the structural basis for how specific lactam compounds bind to RasGRP, offering insights into signaling pathway regulation.
Area of Science:
- Molecular Biology
- Biochemistry
- Structural Biology
Background:
- Ras guanyl releasing protein (RasGRP) is a CDC25 class guanine nucleotide exchange factor regulating Ras-related GTPases, critical for signal transduction.
- RasGRP possesses a C-terminal C1 domain homologous to protein kinase C (PKC) C1 domains, known to bind diacylglycerol and phorbol esters.
- This homology suggests RasGRP functions as a non-kinase phorbol ester receptor, mediating cellular responses through Ras GTPases.
Purpose of the Study:
- To investigate the binding interactions of novel lactam compounds (ILV, 7-(n-octyl)-ILV, benzolactam, and methoxylated benzolactam) with the RasGRP C1 domain.
- To elucidate the structural basis of these interactions using experimental binding assays and molecular modeling.
- To compare the binding characteristics of RasGRP with those of PKC C1 domains.
Main Methods:
- Experimental binding assays were conducted to determine the binding affinities of lactam compounds to RasGRP.
- Homology modeling was employed to generate a structural model of the RasGRP C1 domain (C1-RasGRP).
- Computational docking methods were used to model the complexes of C1-RasGRP with phorbol 13-acetate and the tested lactam ligands.
Main Results:
- The tested lactam compounds exhibited nanomolar binding affinities to RasGRP.
- The structural model of C1-RasGRP showed high similarity to C1b-PKCdelta, featuring antiparallel beta-sheets and an alpha-helix.
- Ligand binding involved hydrogen bonds with residues in loops A and B of C1-RasGRP, with specific interactions varying per ligand and a shallower ligand insertion compared to PKCdelta.
Conclusions:
- The study provides a detailed structural understanding of how phorbol ester-like molecules bind to the RasGRP C1 domain.
- Identified key hydrogen bonding interactions and structural differences (e.g., Phe20 in RasGRP) that dictate ligand binding specificity.
- These findings enhance our comprehension of RasGRP as a phorbol ester receptor and its role in regulating Ras signaling pathways.