Rhodopsin Phosphorylation and Arrestin Activation

Purpose: GPCRs (G-protein coupled-receptors) are the largest class of human membrane protein receptors, and arrestins are critical intracellular modulators of GPCR signaling events. Rhodopsin, the light-sensitive receptor pigment activated by photons within rod cells of the retina, is a class A GPCR which binds to and activates arrestin. Phosphorylation of key residues within rhodopsin introduce a new negative charge density within the C-terminal tail region of rhodopsin, which permits docking of arrestin to rhodopsin and subsequent activation of the bound arrestin. The negatively-charged phosphorylated rhodopsin residues, phosphothreonine (PT336) and phosphoserine (PS338), can undergo favorable charge-based interactions with a set of positively charged arginine (R) and lysine (K) residues that form arrestin's phosphate binding pocket, shown as individual residues in the lower right inset. Lower middle inset visualizes the distribution of electrostatic charge across arrestin's molecular surface as an electrostatic surface potential, the blue surface indicating a region of strong positive charge in the phosphate binding pocket. As shown in the left inset. phosphorylation of the C-terminal tail residues within rhodopsin disrupts the positive and negative charges of the finger loop lock of beta-arrestin-1, causing the finger loop to unlock and arrestin to be activated.

Audience: Academic, with knowledge of GPCRs and phosphorylation 

Medium: Image created using VMD (Visual Molecular Dynamics; Humphrey et al., J. Molec. Graphics, 14:33-38, 1996), Autodesk 3dsMax and Adobe Photoshop.  Structural data for the arrestin-rhodopsin complex was obtained from Protein Databank (PDB file 5WOP; Zhou et al., Cell. 2017 170:457-469, 2017). Distribution of electostratic charge was visualized using APBS (Adaptive Poisson-Boltzmann Solver)-PDBtoPQR software (www.poisson-boltzmann.org; Jurrus et al., Protein Science, 27, 112-128, 2018).

Process Work