Proteins differ from each other in their size, molecular structure and physiochemical properties. These differences allow for protein analysis and characterization by separation and identification.
Proteins are typically separated by electrophoresis, where they are differentiated by size or mass, and isoelectric focusing, where proteins are separated by charge. Protein identification by mass spectrometry involves ionization of molecules to determine their mass-to-charge ratio. Identification can also be done via amino acid sequencing by Edman degradation, crystal imaging and surface plasmon resonance. With so many options available, laboratories typically use multiple strategies for protein analysis and characterization.
Protein expression, purification, labeling, characterization and identification are core methods that are used across a host of molecular biology applications including the development and characterization of biotherapeutic antibodies, and analysis of protein:protein and protein:drug interactions in vitro and in vivo. Molecular tools used for protein analysis are similarly varied, including in vitro protein expression systems, protein purification and pull-down systems, trypsin and other proteases for mass spectrometry, and specific molecular tags for monitoring and imaging proteins in cells.