SIMPLEX Enriches Hydrophobic and Lipidated Proteins in Membrane Proteomics Experiments.

Synaptosomes (Syn) and synaptic junctions (SJ) are key neuronal compartments that have been widely characterized in omics studies to understand neurotransmitter- and signal transduction-related events. While synapses are lipid-rich, multiomics approaches integrating lipids and proteins remain largely underexplored. Liquid-liquid extraction (LLE), commonly used in lipidomics, offers significant potential for multiomics analyses by enabling the extraction of diverse molecular classes from a single sample. However, its impact on protein and phosphoprotein analysis in membrane-enriched samples has not been thoroughly investigated or compared to one-phase extraction methods. In this study, we assessed SIMPLEX (Simultaneous Metabolite, Protein, Lipid Extraction), an LLE-based method, against conventional acetone protein precipitation for mass spectrometry-based protein identification. SIMPLEX proved superior for proteomics and phosphoproteomics of SJ, achieving a 42% enrichment in membrane proteins compared to acetone precipitation. It enriched not only transmembrane proteins but also S-palmitoylated proteins. Enriched phosphoproteins included those with beta-transducin repeats (WD40), Armadillo repeats (ARM), and various transmembrane domains, highlighting the SIMPLEX potential and enhanced performance for multiomics analyses.