Glossary
Recombinant
Recombinant means made by an engineered host cell instead of by chemical synthesis. Where the switch-over from synthesis lies and how the impurities differ.
In recombinant production, the desired peptide or protein is made by a living host cell that has been engineered to contain its gene, instead of being built chemically. Common hosts include E. coli, the yeasts Pichia and Saccharomyces, and mammalian CHO cell lines; the product is subsequently extracted, refolded where required and purified chromatographically.
Chain length decides the route
Which route is used depends on length. Chemical solid-phase synthesis works well up to about 50 residues; past that, accumulated coupling losses push yields too low to be practical. Recombinant expression copes easily with long chains and complete proteins, can form disulfide bonds and, in eukaryotic hosts, add glycosylation. Insulin, growth hormone and full-length thymosin beta-4 are made recombinantly, whereas short signalling peptides and fragments are synthesised.
The two routes leave different impurities, which determines what a certificate of analysis ought to cover. Synthetic batches contain deletion sequences and solvent residues; recombinant batches contain host cell protein, host DNA and — with bacterial hosts — endotoxin, which needs its own test because HPLC purity cannot detect it. Recombinant products also tend to vary more between lots. See how to read a COA.
Related terms
native sequence · analog