Protein Enrichment

Protein enrichment is the purification of a protein or type of protein with a focus on maximizing the yield and the ratio of the desired protein to background in the final product. The generic steps for protein purification are: 1) extraction of proteins through breaking open cells (lysis), 2) precipitation of all proteins in a salt buffer, 3) collection of the precipitated proteins through ultracentrifugation, 4) purification of the desired protein, 5) removal of residual salts, and 6) refolding, if the proteins are denatured (unfolded) during purification. To achieve enrichment, lysis may be performed in several steps to fractionate the cells into membrane, cytoplasmic, nuclear, and cytoskeletal fractions. Furthermore, lysates are often depleted of common contaminating “housekeeping” proteins, such as Gap proteins, actin, and ribosomal proteins, with antibodies or other affinity methods prior to purification to increase the ratio of the desired protein or proteins in the final product. After lysis and precipitation, common methods for purification include size-exclusion chromatography, high performance liquid chromatography (HPLC), and affinity purification. Enrichment can be increased by following the initial purification with additional, alternative purification methods, such as size-exclusion followed by affinity purification. Protein enrichment is necessary to optimize sample collection for low abundance proteins to perform structural analyses and other research techniques, generate antibodies, and manufacture protein-based drugs. (Credit: Brooke Anderson-White)