expressedprotein

Expressed protein is a protein product that is translated from a gene that is actively transcribed in a cell or organism. In molecular biology, the term commonly refers to a recombinant protein produced by a heterologous expression system, where a coding sequence is cloned into an expression vector and expressed in a host organism.

Common expression systems include prokaryotic hosts such as Escherichia coli, eukaryotic microbes like Saccharomyces cerevisiae and Pichia pastoris, insect cells using baculovirus, and mammalian cell lines such as HEK293 or CHO. Expression can be constitutive or inducible, controlled by promoters and inducers. Proteins are frequently fused to affinity tags to simplify purification.

Verification and quantification of expressed protein involve techniques such as SDS-PAGE, Western blotting, ELISA, and mass spectrometry, as well as functional assays. Yields are reported per culture volume or per cell, and may be enhanced by optimizing codon usage, promoter strength, induction conditions, and temperature.

Challenges include improper folding and formation of inclusion bodies in bacterial systems, differences in post-translational modifications (especially glycosylation) between hosts, proteolytic degradation, and purification of tagged versus native forms. Scale-up can introduce issues with stability, solubility, and endotoxin contamination in some hosts.

Applications of expressed proteins span basic research, enzymatic and therapeutic production, vaccine development, and structural biology. The choice of system depends on the required properties of the protein, cost, and regulatory considerations for clinical or industrial use.

See also gene expression, recombinant protein, expression vector, host organism.