Chemical modifications to enhance proteomics analysis
The high-throughput analysis of proteins, the field known as proteomics, has revolutionised modern biology by comparing protein content among cells or tissues. Given the fundamental functional importance of proteins in any living being, proteomics constitutes a valuable tool for the analysis of perturbed protein signalling encountered in disease. The EU-funded 'Detecting protease substrates using unnatural amino acids' (TAGGING PROTEOLYSIS) project proposed using the method of arginylation for proteomics. Arginylation is an enzymatic process that adds a basic amino acid to the N-terminus of a peptide. This is useful for proteomics analysis using electro spray mass spectrometry where a proton is attached to a peptide, usually to basic amino acids. Basic residues on the C-terminus of a peptide can be generated during trypsin digest, but the N-terminus typically lacks basic amino acids. Apart from increasing the charge state of the peptide, conjugation of an arginyl moiety to the N-terminus of a peptide could be used to detect shorter peptides. Additionally, by combining a charge on the N-terminus together with a basic residue on the C-terminus, scientists were able to perform bi-directional peptide sequencing. This led to the precise determination of phosphorylation sites in peptides that are critical for signalling cascades and may correlate with disease progression or prognosis. The method of arginylation offers advantages to peptide synthetic chemistry as it allows peptide synthesis with both N- and C-terminal basic amino acids. Furthermore, it could be used to enhance disease clinical diagnosis through specialised ELISA assays that detect perturbed phosphorylation sites.
