An arrestin-1 surface opposite of its interface with photo-activated rhodopsin engages with enolase-1.

Arrestin-1 is the arrestin-family member responsible for inactivation of the G protein-coupled receptor rhodopsin in photoreceptors. Arrestin-1 is also well known to interact with additional protein partners and to affect other signaling cascades beyond phototransduction. In this study, we investigated one of these alternative arrestin-1 binding partners, the glycolysis enzyme enolase-1, to map the molecular contact sites between these two proteins and investigate how the binding of arrestin-1 affects the catalytic activity of enolase-1. Using fluorescence quench protection of strategically placed fluorophores on the arrestin-1 surface, we observed that arrestin-1 primarily engages enolase-1 along a surface that is opposite of the side of arrestin-1 that binds photo-activated rhodopsin. Using this information, we developed a molecular model of the arrestin-1 - enolase-1 complex, which was validated by targeted substitutions of charged-pair interactions. Finally, we identified the likely source of arrestin's modulation of enolase-1 catalysis, showing that selective substitution of two amino acids in arrestin-1 can completely remove its effect on enolase-1 activity while still remaining bound to enolase-1. These findings open up opportunities for examining the functional effects of arrestin-1 on enolase-1 activity in photoreceptors and their surrounding cells.