Arginine PTM analysis

Arginine plays a critical role in protein structure and function and often mediates key interactions between protein binding partners or between proteins and DNA. The two most common arginine PTMs are citrullination and dimethylation, which respectively alter arginine into citrulline or ADMA and SDMA.

ADMA and SDMA isomers share structural similarities and an identical mass, limiting their identification through traditional mass spectrometry. Likewise, determining arginine to citrulline results in a negligible mass increase. Another common method for PTM detection is antibody-based immunoassay ELISA, but only a few antibodies against arginine PTMs are commercially available, restricting its application.

Direct detection of arginine PTMs in proteins with Platinum

With Platinum’s single-molecule resolution and sensitivity, you can detect and differentiate arginine PTMs accurately. Peptide fragments are probed in real-time by fluorescently labeled recognizers, designed to bind on and off to their cognate N-terminal amino acid (NAA), while aminopeptidases in solution remove analyzed NAAs to expose subsequent amino acids for further recognition. Fluorescence lifetime, intensity, and kinetic data are collected in real-time and analyzed to determine amino acid sequence and PTM content. This novel single-molecule sequencing approach can overcome the challenges facing conventional methods through unparalleled amino acid detection.

Using Quantum-Si’s single-molecule protein sequencing, we demonstrated how to detect citrulline and how to differentiate between dimethylated arginine residues efficiently.