# Systematic analysis of the RGS2 degron reveals characteristics of substrate recognition by the F-box protein FBXO44

## TL;DR

This study identifies key features of how RGS2 protein is recognized by FBXO44, offering insights for drug development to increase RGS2 levels in diseases.

## Contribution

The study systematically defines the RGS2 degron and its interaction with FBXO44, providing a structural framework for drug design and substrate discovery.

## Key findings

- Peptide array and computational modeling identified amino acid changes affecting FBXO44 binding to RGS2.
- Experimental validation confirmed the role of specific residues in RGS2–FBXO44 interaction.
- Results offer structural insights for designing drugs and predicting additional FBXO44 substrates.

## Abstract

Regulator of G protein signaling 2 (RGS2) negatively modulates signaling downstream of G protein–coupled receptors by accelerating GTP hydrolysis at Gα subunits of heterotrimeric G proteins. Decreased RGS2 levels are implicated in numerous diseases, including cardiovascular disease and asthma. Thus, identifying selective means of enhancing RGS2 protein levels would be a viable therapeutic strategy. RGS2 is rapidly degraded through the ubiquitin–proteasomal pathway, and we previously identified F-box only protein 44 (FBXO44) as the substrate recognition component of the E3 ligase responsible for facilitating RGS2 degradation. As such, the RGS2–FBXO44 interaction is a potential target for pharmacological intervention. Detailed information on the FBXO44 recognition site (degron) in RGS2 will aid in structure-based small-molecule inhibitor design, as well as in identifying additional FBXO44 targets, which would help predict possible side effects of targeting this interaction. Thus, the goal of this study was to dissect the molecular properties for FBXO44 binding of the RGS2 degron. We used a peptide array utilizing systematic residue substitution, combined with AlphaFold modeling and molecular dynamics simulations, to identify several amino acid changes that altered binding both positively and negatively. Finally, we experimentally confirmed our results in cells through coimmunoprecipitation and proteasomal inhibition, using full-length RGS2. Altogether, these results provide structural insights into RGS2–FBXO44 binding, which will aid in structure-guided drug discovery efforts. It also provides a framework for building a consensus recognition motif for FBXO44, which could aid in identifying more substrates for this understudied F-box protein.