Co-Translational Protein Folding in Prokaryotic and Eukaryotic Cell-Free Translation Systems

Abstract

Native structure formation of newly synthesized proteins is a key problem relating to the cell-free translation technology that is aimed at the synthesis of biologically active products. At the same time, a lot of experimental data indicate that the folding of newly synthesized proteins differs significantly from the in vitro process observed by Anfinsen in his classical experiments on the refolding of ribonuclease (Anfinsen 1973) and studied in detail by many other workers. The difference results mainly from (i) the contribution of multiple cellular components, such as protein disulphide isomerase, peptidylprolyl isomerase, and molecular chaperones that catalyze or assist the folding of synthesized proteins (Gething and Sambrook 1992; Georgopoulos and Welch 1993; Ellis 1994; Hartl 1996; Fink 1999), and (ii) the co-translational mode of the folding, implying that the N-terminal part of a nascent peptide starts its folding as soon as it is synthesized and emerges from the ribosome prior to the formation of the entire polypeptide chain (see refs below). The existence of stepwise protein folding starting from the N-terminal section of a growing polypeptide and progressively proceeding towards the C-terminus was first proposed by Phillips et al. (1967) from theoretical analysis of the folding pattern of hen egg lysozyme. Later, several experimental approaches demonstrated co-translational formation of native or native-like structure of nascent polypeptides, both in vitro and in vivo. It was shown that growing polypeptides are able to interact with free sub-units of the same protein, thus being involved in the assembly of quaternary structures on ribosomes (Kiho and Rich 1964; Gilmore et al. 1996).