Title

An investigation of the structural elements that underlie the arrestin mediated desensitization and internalization of cannabinoid receptor 1

Date of Completion

January 2009

Keywords

Chemistry, Pharmaceutical

Degree

Ph.D.

Abstract

Arrestins are cytosolic proteins that mediate the desensitization and internalization of G-Protein Coupled Receptors (GPCRs). Ligands bind and stabilize conformations of GPCR cytosolic loops that can couple to and activate G-Proteins. Following activation, the GPCR C-terminus is phosphorylated by G-Protein Coupled Receptor Kinases (GRK) and subsequently interacts with arrestin leading to desensitization and internalization of GPCRs. Internalization is followed by trafficking of the receptor to pathways that couple to alternate signaling pathways, recycle it to the cell surface or degrade it. An emerging concept in the literature is that arrestins display more than one conformation when bound, leading to alternate complexes that have different functional outcomes. The precise detail of these events is not known. Concomitantly there is no direct structural information on the bound state of the GPCR C-terminus and conflicting evidence as to the importance of phosphorylation in directing the formation of the bound arrestin conformations. Recent biological evidence suggests that the disposition of the cytosolic face of the GPCR holds sway in the adoption of a specific conformation. ^ The aims of this research are to study conformations of synthetic peptides derived from segments of CB1 shown to be responsible for desensitization and internalization, effect of the phosphorylation pattern on the conformations of the peptides and binding of these peptides to arrestin-2.^ To shed further light on the interaction between these peptides and arrestin, we investigated their effects on the HSQC spectra of arrestin. In our study, we observed that phosphorylation of the peptide was necessary for binding and the formation of short helical segments in bound peptides was a common structural element. By comparing the binding of these different segments we conclude that while phosphorylation is necessary for affinity, the primary amino acid sequence of the peptides can affect the final bound conformation. The NOE data of the bound peptides and mutational studies of arrestin taken from the literature were used to predict models describing the interaction interface between arrestin and peptides using the docking program. This study will expand our knowledge of signal transduction and may provide avenues for novel methods of modulating GPCR function. ^