Protein Chemistry. Structure, Properties, Research Methods - Shendryk A.N. 2022

Protein Structure
Protein Structure
Fragmentation of Protein Chains

Edman Degradation, the chemical Cleavage of short Peptides or protein chain fragments, remains the only direct method for peptide sequencing today. It involves the successive cleavage and identification (as a thiohydantoin derivative) of one amino acid residue at a time from the N-terminus of the chain. However, even with an automated Sequencer, the maximum number of consecutive Edman degradation cycles is currently limited to 20–40 amino acid residues. There are reports of successful sequencing operations for peptide fragments containing 40–60 Amino Acids in the chain. The polypeptide chains of many Proteins are substantially longer. For example, the human Hemoglobin α-chain contains 141 residues, Growth Hormone contains 181, and the enzyme glyceraldehyde dehydrogenase contains 332. Such long chains cannot be directly analyzed by the Edman method. Therefore, the following strategy is employed: large peptide chains are cleaved into relatively short fragments, each of which is isolated and sequenced via Edman degradation. The primary challenge with this approach lies in ensuring the Selective Cleavage of the peptide chain at specific peptide bonds. Such Specificity is achieved through The Use of Enzymes or specialized chemical agents.