Through the looking glass - a new world of proteins enabled by chemical synthesis

Chemical ligation the regioselective and chemoselective covalent condensation of unprotected peptide segments has enabled the synthesis of polypeptide chains of more than 200 amino acids. An efficient total chemical synthesis of the insulin molecule has been devised on the basis of a key ester-linked intermediate that is chemically converted to fully active human insulin. Enzyme molecules of defined covalent structure and with full enzymatic activity have been prepared and characterized by high-resolution X-ray crystallography. A glycoprotein mimetic of defined chemical structure and with a mass of 50,825?Da, has been prepared and shown to have full biological activity and improved pharmacokinetic properties. d-Protein molecules that are the mirror images of proteins found in the natural world have been prepared by total chemical synthesis. Racemic protein mixtures, consisting of the d-enantiomers and l-enantiomers of a protein molecule, form highly ordered centrosymmetric crystals with great ease; this has enabled the determination of the crystal structures of recalcitrant protein molecules. A protein with a novel linear-loop covalent topology of the peptide chain has been designed and synthesized and its structure determined by facile crystallization as the quasi-racemate with the d-form of the native protein molecule. We have developed an optimized total chemical synthesis of biologically active vascular endothelial growth factor-A; total synthesis of the mirror-image protein will be used to systematically develop d-protein antagonists of this important growth factor. The total chemical synthesis of proteins is now a practical reality and enables access to a new world of protein molecules. Copyright (C) 2012 European Peptide Society and John Wiley & Sons, Ltd.