Protein concentration is determined using absorbance at 280nm, correcting for the extinction coefficient. LC mass spectrometry is used in two ways: to determine the intact mass of the protein to search for post-translational modifications if feasible and to peptide map after proteolytic digestion. The thermal stability of the protein can also be monitored using a thermal shift assay. This can be particularly useful to infer a folded state and to monitor compound binding if this shifts the melting point.
Post-translational modifications are very important to the folding and function of many proteins. We have significant experience of analysing these modifications using mass spectrometry and altering them as required. We have worked with proteins that are N and O-glycosylated, disulphide bonded, phosphorylated, lipid modified, proteolytically activated, poly-ADP ribosylated and many other modifications.