Fatty-acylation in RAW264.7 - Bioorthogonal Chemical Reporters for Monitoring Unsaturated Fatty-Acylated Proteins

Dietary unsaturated fatty acids beneficially affect human health, in part by modulating the immune system, but the mechanism is not completely understood. Given that unsaturated fatty acids have been shown to be covalently incorporated into a small subset of proteins, we designed three alkyne-tagged chemical reporters of unsaturated fatty acids, alk-16:1, alk-17:1 and alk-18:1, to explore the generality and diversity of this protein modification. Following cell lysis, proteins labelled with the reporters could be captured by azido-functionalized reagents via CuAAC for fluorescence detection or enrichment for proteomics analysis. These reporters label many proteins in mammalian cells and can be incorporated site-specifically, notably on Cys residues. Quantitative proteomics analysis (n= 4 biological replicates) of LPS/IFN-gamma stimulated RAW264.7 labelled with oleic acid (control), alk-16 (palmitic acid chemical reporter), alk-16:1, alk-17:1 and alk-18:1, revealed that unsaturated fatty acids modify similar protein targets to saturated fatty acids, including several immune proteins. Interestingly, some proteins can be differentially labeled with unsaturated and saturated fatty acid.