Peptide bonds, selective cleavage

Chemical modification of amino acid side chain functionalities will also serve to cleave specific peptide bonds selectively. Chemical cleavage of a polypeptide chain exploits the unique reactivity of chemically modified side chains of particular amino acids in the labilization of adjacent peptide bonds by neighbouring group participation (68). The residues investigated so far for this purpose have been methionine, cysteine and the aromatic amino acids including tryptophan (438-440, 443). 

Selective hydrolysis can be accomplished by using enzymes to catalyze cleavage at specific peptide bonds... 

Chymotrypsin (Section 27 10) A digestive enzyme that cat alyzes the hydrolysis of proteins Chymotrypsin selectively catalyzes the cleavage of the peptide bond between the car boxyl group of phenylalanine tyrosine or tryptophan and some other ammo acid... 

Selective cleavage of peptides and proteins is an important procedure in biochemistry and molecular biology. The half-life for the uncatalyzed hydrolysis of amide bonds is 350 500 years at room temperature and pH 4 8. Clearly, efficient methods of cleavage are needed. Despite their great catalytic power and selectivity to sequence, proteinases have some disadvantages. Peptides 420,423,424,426 an(j proteins428 429 can be hydrolytically cleaved near histidine and methionine residues with several palladium(II) aqua complexes, often with catalytic turnover. 

T. Hashimoto, S. Saito, K. Ohki, N. Sakura, Highly Selective Cleavage of Pyroglutamyl-Peptide Bond in Concentrated Hydrochloric Acid , Chem. Pharm. Bull. 1996, 44, 877-879. 

Proteases, since their discovery, have played an important role in both basic and applied research because their sometimes exquisite selectivity of peptide bond cleavage can be extremely useful in the elucidation of other proteins structures and function. The following three sub-sections give several examples of how proteases are used in specific aspects of research. 

Picornain 2A [EC 3.4.22.29] catalyzes the hydrolysis of peptide bonds including the selective cleavage of a particular peptide bond in the picornavirus polyprotein. Picornain 3C [EC 3.4.22.28] catalyzes the selective hydrolysis of the Gin—Gly bond in the poliovirus polyprotein. 

Thrombin [EC 3.4.21.5], also known as fibrinogenase, catalyzes the hydrolysis of peptide bonds, exhibiting preferential cleavage for the Arg—Gly peptide bond. The enzyme, a member of the peptidase family SI, activates fibrinogen to fibrin and releases fibrinopeptide A and B. Thrombin, formed from prothrombin, is more selective in peptide hydrolysis than trypsin or plasmin. 

Zhu, J. X. and Aswad, D. W. (2007). Selective cleavage of isoaspartyl peptide bonds by hydroxylamine after methyltransferase priming. Anal. Biochem. 364,1-17. 

The porcine insulin is first subjected to digestion with chymotrypsin-free trypsin at pH 7.5 for in excess of 45 min. This results in the selective cleavage of the peptide bond linking arginine 22... 

Chemical cleavage at selective amino acid residues is an alternative method for scission of peptide bonds in target molecules. Cleavage at the Met-Xaa bond is achieved by CNBr, at the Trp-Xaa bond by the tryptophan-directed reagent 3-bromo-3-methyl-2-[(2-nitro-phenyl)sulfanyl]-3//-indole (BNPS-skatole) and at the Asp-Xaa bond by 2% formic acid.123 24 All these reactions are carried out at acidic pH under standard conditions for each reagent. 

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