Sandbox Reserved 198: Difference between revisions

Peptide synthesis is the production of proteins in which multiple amino acids are linked together through peptide bonds. A general chemical requirement for peptide synthesis is the blockage of the carboxyl group of one amino acid and the amino group of the second amino acid. The carboxyl group of the free carboxyl group can be activated and the new peptide bond is formed (Merrifield, 1984). A common type of peptide synthesis is the solid-phase synthesis, in which the end of the peptide chain is attached to a solid support, as shown in Figure 1.  

The semi-synthetic RNase A comprises of residues 1-118 and the synthetic analog of residues 111-124. The RNase 1-118 was prepared by successive digestion of RNase A pepsin and carboxypeptidase A (Doscher, 1983). The synthetic component, RNase 111-124, was prepared by the use of solid-phase peptide synthetic methods, in which the peptide chain was assembled in the stepwise manner while it was attached at one end to a solid support. The peptide chain was extended by repetitive steps of de-protection, neutralization and coupling until the desired sequence was obtained (Lin, 1970). It was important that the synthesis proceeds rapidly and in high yields to prevent side reactions or by-products.

The peptide ligation chemistry in addition to solid-phase peptide synthesis is used to synthesize relatively longer peptide molecules with typical length of 125 residues (Boerema, 2007). The ligation methods overcome the length limitation of solid-phase synthesis, because the chemical ligation involves the joining of mutually reactive peptide segments created by solid-phase synthesis. The peptide bond in ligation is formed between an unprotected peptide and a peptide-thioester (Boerema, 2007). The shorter peptide segments are more rapidly prepared and are less susceptible to solubility issues in longer peptide chains.  

The <scene name='Sandbox_Reserved_198/Fully_synthetic/4'>Fully Synthetic RNase A</scene> (124 residues) is prepared by two consecutive sets of one-pot ligations and related chemical transformations of six peptide segments (residues 1-25, 26-39, 40-64, 65-83, 84-94, 95-124) (Boerema, 2007),which can prevent undesired byproduct formation. The six unprotected peptide segments were synthesized by highly optimized, stepwise solid-phase synthesis. This synthetic pathway is simple, has high overall yields, and it eliminate the need for the isolation of intermediate products.