Shotgun Protein Analysis by Liquid Chromatography-Tandem Mass Spectrometry

Two-dimensional electrophoresis (2DE) is an excellent technology for the analysis of complex protein mixtures, but it has drawbacks, such as hardly detecting very hydrophobic proteins. Shotgun protein analysis is one of the major technologies used to compensate for the weaknesses of 2DE. In this approach, total proteins are digested as a mixture and the digested peptides are separated by one-dimensional or multidimensional chromatography and introduced into a tandem mass spectrometer. Since the shotgun approach is the primary strategy in proteomics besides 2DE, a great number of related methodologies have been developed. In this chapter, we would like to introduce the simplest protocol, in which proteins are digested in solution and the digested peptides are analyzed by one-dimensional reversed-phase liquid chromatography coupled with tandem mass spectrometry (LC–MS/MS), as a starting point for shotgun protein analysis.