Production of Soluble Recombinant Proteins in Bacteria

Abstract

Production of recombinant proteins in bacteria is limited by the formation of cytoplasmic aggregates (inclusion bodies or “IBs”). This review summarizes what is known about why IBs form and ways of increasing the production of soluble protein in bacterial systems. The easiest way to lower IB formation is to reduce the growth temperature of the bacteria. IB formation is not directly correlatable with the production rate, nor with the size of the produced protein. The primary sequences of a few proteins that do not form IBs at higher production temperatures contain either a low content of proline residues or stretches of acidic amino acids. Metal ion binding may also lower the tendency to form IBs at growth temperatures above 30°C. Three aspects of protein synthesis in mammalian cells, compartmentation, interprotein interactions (sortases, foldases, unfoldases, and chaperonins), and post-translational modifications, have significant effects on the solubility of the proteins produced. Possibilities for mimicking these mechanisms in bacteria via secretion, cloning of mammalian foldases, and mutation of the post-translational modification systems of the host bacteria are discussed.