Protein expression refers to the process of synthesizing a protein in a living cell or in a laboratory setting. Protein expression is a critical step in many areas of biological research, including drug development, functional genomics, and structural biology.

This can be achieved using a variety of methods, including recombinant DNA technology, protein synthesis using cell-free systems, and in vivo expression in living cells. Recombinant DNA technology involves inserting a gene of interest into a vector, such as a plasmid, that can be introduced into a host cell, such as bacteria or mammalian cells. The host cell then uses its own machinery to synthesize the protein encoded by the inserted gene. Protein synthesis using cell-free systems involves synthesizing the protein in vitro, outside of a living cell, using purified components. In vivo expression in living cells involves introducing the gene of interest into a living organism, such as a plant or animal, and allowing the organism to produce the protein.

Once the protein is synthesized, it can be purified and characterized for further study. Purification methods may include chromatography, filtration, and electrophoresis. Characterization methods may include mass spectrometry, circular dichroism, and X-ray crystallography.

Protein expression has many applications in basic and applied research. It is used to study the function and structure of proteins, to produce therapeutic proteins for the treatment of diseases, and to develop vaccines and other biopharmaceuticals.