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Papain, also known as papaya proteinase I, is a cysteine protease (EC 3.4.22.2) enzyme present in papaya ... Papain on Proteopedia (wiki with more protein specific info)
The structure of papain was among the earliest protein structures experimentally determined by X-ray crystallography. [3] [10] [9] Many papain-like protease enzymes function as monomers, though a few, such as cathepsin C (Dipeptidyl-peptidase I), are homotetramers.
Discovered by Gopal Chunder Roy in 1873, the first cysteine protease to be isolated and characterized was papain, obtained from Carica papaya. [1] Cysteine proteases are commonly encountered in fruits including the papaya, pineapple, fig and kiwifruit. The proportion of protease tends to be higher when the fruit is unripe.
The protein is 216 amino acids in length, and is 68% identical in sequence to papain, 65% to chymopapain and 81% to glycyl endopeptidase. The three disulfide bonds are conserved between all the papaya proteinases, and there is no evidence for glycosylation. Caricain is an extremely basic protein, with pI estimated to be 11.7.
Chymopapain (EC 3.4.22.6, chymopapain A, chymopapain B, chymopapain S, brand name Chymodiactin) is a proteolytic enzyme isolated from the latex of papaya (Carica papaya).It is a cysteine protease which belongs to the papain-like protease (PLCP) group. [1]
The nidoviral papain-like protease (PLPro or PLP) is a papain-like protease protein domain encoded in the genomes of nidoviruses.It is expressed as part of a large polyprotein from the ORF1a gene and has cysteine protease enzymatic activity responsible for proteolytic cleavage of some of the N-terminal viral nonstructural proteins within the polyprotein.
Actinidain is similar to papain in size, shape, active site location and conformation, as well as in kinetic studies, which is especially interesting as they only share 48% amino acid similarity. [ 2 ] [ 14 ] Electron density mapping shows similar α-helices and overall polypeptide folding.
An antibody digested by papain yields three fragments, two Fab fragments and one Fc fragment An antibody digested by pepsin yields two fragments: a F(ab') 2 fragment and a pFc' fragment The fragment crystallizable region ( Fc region ) is the tail region of an antibody that interacts with cell surface receptors called Fc receptors and some ...