# Discovery and Profiling of Protein Cysteine S-2-Carboxypropylation

## TL;DR

This paper discovers a new protein modification called S-2-carboxypropylation and shows it affects many cellular functions, offering new insights into valine metabolism and disease.

## Contribution

The study identifies and validates a novel protein post-translational modification, S-2-carboxypropylation, using a bioorthogonal probe and chemical proteomics.

## Key findings

- A bioorthogonal probe successfully detected and profiled S-2-carboxypropylated proteins in mammalian cells.
- 403 modified proteins and 120 cysteine sites were identified in HEK293T cells.
- C2cp-modified proteins are involved in translation, RNA splicing, and protein folding.

## Abstract

Methacrylyl-CoA is a key metabolic intermediate in the valine catabolic pathway. Its accumulation has been found to be cytotoxic and associated with pathological conditions. Nevertheless, detailed biological effects of methacrylyl-CoA and methacrylate in human physiology and pathology are poorly understood. We propose that the electrophilicity of the alkene bond in the methacrylyl group can react with the cysteine residues in proteins resulting in an unexplored protein post-translational modification (PTM), cysteine S-2-carboxypropylation (C2cp). To test and validate this mechanistic hypothesis, we experimentally detected and profiled S-2-carboxypropylated proteins from the complex cellular proteome with the design and application of a bioorthogonal chemical probe, N-propargyl methacrylamide. We tested the probe in different mammalian cell models and demonstrated its versatility and sensitivity to protein cysteine S-2-carboxypropylation. We established quantitative chemical proteomics for global and site-specific profiling of protein S-2-carboxypropylation, which successfully identified 403 S-2-carboxypropylated proteins and 120 cysteine modification sites from HEK293T cells. Through bioinformatic analysis, we found that C2cp-modified proteins were involved in a variety of critical cellular functions including translation, RNA splicing, and protein folding. Our chemoproteomic studies demonstrating the proteome-wide distribution of cysteine S-2-carboxypropylation provide a new biochemical mechanism for the functional investigation of methacrylyl-CoA and understanding valine-related metabolic disorders.