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出典:『Wikipedia』 (2011/04/14 11:43 UTC 版)

英語による解説

引用

The term Oligopeptidase was coined by Camargo in 1979 to designate a sub-group of the endopeptidases that are specialized in the hydrolysis of peptides, and do not act on proteins. The selection of substrates by size is not the only feature that turns the oligopeptidase peculiar among the digestive (pancreatic enzymes, proteasomes, cathepsins) or processing (pro-hormone convertases, calpains, caspases) endopeptidases. The oligopetidases have a less accessible pocket harboring their active sites. Moreover, both, enzymatic and crystallographic studies have shown that the susceptibility of the peptide bond cannot be described according to Berger and Schechter, which is the guide frame for the understanding of endopeptidase specificities in general. This peculiar mechanism of action sets the oligopeptidases at the end of the protein processing pathway, acting on specific oligopeptides, allowing them to play essential physiological and pathological roles, from microorganisms to man. The prolyl-oligopeptidase (POP), a post-proline cleaving enzyme, is a good example of how an oligopeptidase interacts with and metabolizes an oligopeptide. The peptide has first to penetrate into a 4 Å hole on the surface of the enzyme in order to reach an 8,500Å3 internal cavity, where the active site is located. Li et al. presented a convincing example of substrate size restriction for catalysis using a peptide of 35 amino acid residues containing a single proline at position 10. This peptide, with 35 amino acid residues, is small enough to get inside POP while the enzyme is opened. However, it is resistant to digestion, whereas its fragment of 22 amino acid is completely digested. As it has been suggested by enzymatic kinetic studies the physical step involving conformational change of the peptide is the rate-limiting step leading to chemical catalysis. The enzyme acts by facilitating an induced fit. On the other hand, the induced fit mechanism may be beneficial to the fidelity of the molecular recognition in the presence of a huge competition by other peptides via the conformational proofreading mechanism.