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35-492: It has wide ranging commercial applications in the leather, cosmetic, textiles, detergents, food and pharmaceutical industries. In the food industry, papain is used as an active ingredient in many commercial meat tenderizers. Papain belongs to a family of related proteins, known as the papain-like protease family, with a wide variety of activities, including endopeptidases , aminopeptidases , dipeptidyl peptidases and enzymes with both exo- and endopeptidase activity. Members of

70-1039: A cathepsin L -like enzyme. Cysteine cathepsins are also part of the normal life cycle of the unicellular parasite Leishmania , where they function as virulence factors . The enzyme and potential drug target cruzipain is important for the life cycle of the parasite Trypanosoma cruzi , which causes Chagas' disease . Members of the papain-like protease family play a number of important roles in plant development , including seed germination , leaf senescence , and responding to abiotic stress . Papain-like proteases are involved in regulation of programmed cell death in plants, for example in tapetum during development of pollen . They are also important in plant immunity providing defense against pests and pathogens . The relationship between plant papain-like proteases and pathogen responses—such as cystatin inhibitors —have been described as an evolutionary arms race . Some PLP family members in plants have culinary and commercial applications. The family's namesake member, papain ,

105-675: A common catalytic dyad active site featuring a cysteine amino acid residue that acts as a nucleophile . The human genome encodes eleven cysteine cathepsins which have a broad range of physiological functions. In some parasites papain-like proteases have roles in host invasion, such as cruzipain from Trypanosoma cruzi . In plants, they are involved in host defense and in development. Studies of papain-like proteases from prokaryotes have lagged their eukaryotic counterparts. In cellular organisms they are synthesized as preproenzymes that are not enzymatically active until mature, and their activities are tightly regulated, often by

140-477: A degenerated disc disease model to assess various types of injectable therapies. An antibody digested by papain yields three fragments: two 50 kDa Fab fragments and one 50 kDa Fc fragment . The papain-digested antibody is unable to promote agglutination , precipitation , opsonization , and lysis , however, the Fab fragment is still able to bind to and neutralize appropriate antigens, most commonly seen in

175-475: A large protein family of cysteine protease enzymes that share structural and enzymatic properties with the group's namesake member, papain . They are found in all domains of life . In animals, the group is often known as cysteine cathepsins or, in older literature, lysosomal peptidases . In the MEROPS protease enzyme classification system, papain-like proteases form Clan CA . Papain-like proteases share

210-507: A large polyprotein into viral nonstructural proteins , although they perform fewer cleavages than the 3C-like protease (also known as the main protease). Coronavirus PLPs are multifunctional enzymes that can also act as deubiquitinases (cleaving the isopeptide bond to ubiquitin ) and "deISGylating enzymes" with analogous activity against the ubiquitin-like protein ISG15 . In human pathogens including SARS-CoV , MERS-CoV , and SARS-CoV-2 ,

245-524: A noticeable effect. Papain is the main ingredient of Papacarie, a gel used for chemomechanical dental caries removal. It does not require drilling and does not interfere in the bond strength of restorative materials to dentin . Papain has been known to interfere with urine drug tests for cannabinoids . It is found in some drug detox products. Recently, it has been demonstrated that papain can be used to assemble thin films of titania used in photovoltaic cells . Papain has also been used to create

280-500: A number of physiological processes and disease states. As part of normal physiological processes, they are involved in key steps of antigen presentation as part of the adaptive immune system , remodeling of the extracellular matrix , differentiation of keratinocytes , and processing of peptide hormones . Cysteine cathepsins have been associated with cancer and tumor progression , cardiovascular disease , autoimmune disease , and other human health conditions. Cathepsin K has

315-475: A role in bone resorption and has been studied as a drug target for osteoporosis . A number of parasites , including helminths (parasitic worms), use papain-like proteases as mechanisms for invasion of their hosts . Examples include Toxoplasma gondii and Giardia lamblia . In many flatworms, there are very high levels of expression of cysteine cathepsins; in the liver fluke Fasciola hepatica , gene duplications have produced over 20 paralogs of

350-592: A serious drop in blood pressure and increased heart rate from the topical papain products," said Janet Woodcock , director for the Center for Drug Evaluation and Research . Topical drug ointments containing papain are used to remove dead or contaminated tissue in acute and chronic lesions, such as diabetic ulcers, pressure ulcers, varicose ulcers, and traumatic infected wounds. Trade names for these products include Accuzyme, Allanfil, Allanzyme, Ethezyme, Gladase, Kovia, Panafil, Pap Urea, and Ziox. Other products are marketed under

385-532: Is a protease derived from papaya , used as a meat tenderizer . Similar but less widely used plant products include bromelain from pineapple and ficin from figs . Although papain-like proteases are found in all domains of life , they have been less well-studied in prokaryotes than in eukaryotes . Only a few prokaryotic PLP enzymes have been characterized by X-ray crystallography or enzymatic studies, mostly from pathogenic bacteria, including streptopain from Streptococcus pyogenes ; xylellain , from

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420-409: Is also used as an ingredient in various enzymatic debriding preparations, notably Accuzyme. These are used in the care of some chronic wounds to clean up dead tissue. Papain is added to some toothpastes and mint sweets as a tooth whitener. Its whitening effect is minimal, because the papain is present in low concentrations and is quickly diluted by saliva. It would take several months of use to have

455-624: Is characteristically divided into two lobes or subdomains, known as the L-domain ( N-terminal ) and the R-domain ( C-terminal ), where the active site is located between them. The L-domain is primarily helical while the R-domain contains beta-sheets in a beta-barrel -like shape, surrounded by a helix. The enzyme substrate interacts with both domains in an extended conformation. Papain-like proteases are often synthesized as preproenzymes , or enzymatically inactive precursors. A signal peptide at

490-408: Is made up of the amino acids cysteine-25 (from which it gets its classification) and histidine-159. Aspartate-158 was thought to play a role analogous to the role of aspartate in the serine protease catalytic triad, but that has since been disproved. The mechanism by which papain breaks peptide bonds involves the use of a catalytic dyad with a deprotonated cysteine. A nearby Asn-175 helps to orient

525-463: The N-terminus , which serves as a subcellular localization signal, is cleaved by signal peptidase to form a zymogen . Post-translational modification in the form of N-linked glycosylation also occurs in parallel. The zymogen is still inactive due to the presence of a propeptide which functions as an inhibitor blocking access to the active site. The propeptide is removed by proteolysis to form

560-414: The imidazole ring of His-159 to allow it to deprotonate the catalytic Cys-25. This cysteine then performs a nucleophilic attack on the carbonyl carbon of a peptide backbone. This forms a covalent acyl-enzyme intermediate and frees the amino terminus of the peptide. The enzyme is deacylated by a water molecule and releases the carboxy terminal portion of the peptide. In immunology, papain is known to cleave

595-471: The Fc (crystallisable) portion of immunoglobulins (antibodies) from the Fab (antigen-binding) portion. Papain is a relatively heat-resistant enzyme, with an optimal temperature range of 60 to 70 °C. Papain prefers to cleave after an arginine or lysine preceded by a hydrophobic unit ( Ala , Val , Leu , Ile , Phe , Trp , Tyr ) and not followed by a valine . Papain breaks down tough meat fibres, and

630-524: The PLP domain is essential for viral replication and is therefore considered a drug target for the development of antiviral drugs . One such experimental antiviral medication, Jun12682 , is being studied as a potential treatment for COVID-19, and it is believed to work by inhibiting SARS-CoV-2 papain-like protease (PLpro). Trituration Trituration (Latin, grinding ) is the name of several different methods used to process materials. In one sense, it

665-590: The US Food and Drug Administration (FDA) warned companies to stop marketing ophthalmic balanced salt solutions and topical drug products containing papain by November 4, 2008. The FDA said, "Papain-containing drug products in topical form historically have been marketed without approval...". According to the FDA's statement on the subject, "These unapproved products have put consumers' health in jeopardy, from reports of permanent vision loss with unapproved balanced salt solutions to

700-413: The extracellular matrix molecules holding the cells together. After ten minutes, the tissue should be treated with a protease inhibitor solution to stop the protease action. Left untreated, papain activity will lead to complete lysis of the cells. The tissue must then be triturated (passed quickly up and down through a Pasteur pipette ) to break up the pieces of tissue into a single cell suspension . It

735-413: The fruit or drip into a container. This latex is then further dried. It is now classified as a dried, crude material. A purification step is necessary to remove contaminating substances. This purification consists of the solubilization and extraction of the active papain enzyme system through a government-registered process. This purified papain may be supplied as powder or as liquid. On September 23, 2008,

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770-405: The mature enzyme. Papain-like proteases have a catalytic dyad consisting of a cysteine and a histidine residue, which form an ion pair through their charged thiolate and imidazolium side chains. The negatively charged cysteine thiolate functions as a nucleophile . Additional neighboring residues— aspartate , asparagine , or glutamine —position the catalytic residues; in papain,

805-402: The mature peptide (134-345). The amino acid numbers are based on the mature peptide. The protein is stabilised by three disulfide bridges . Its three-dimensional structure consists of two distinct structural domains with a cleft between them. This cleft contains the active site , which contains a catalytic dyad that has been likened to the catalytic triad of chymotrypsin . The catalytic dyad

840-465: The names of the active ingredients, for instance, papain-urea ointment. In 2008 the FDA announced its intention to take action against these products because it had received reports of serious adverse events in patients using products containing papain. Reports included hypersensitivity (allergic) reactions that lead to hypotension (low blood pressure) and tachycardia (rapid heart rate). In addition, people allergic to latex can also be allergic to papaya,

875-510: The papain family are widespread, found in baculoviruses , eubacteria, yeast, and practically all protozoa, plants and mammals. The proteins are typically lysosomal or secreted, and proteolytic cleavage of the propeptide is required for enzyme activation, although bleomycin hydrolase is cytosolic in fungi and mammals. Papain-like cysteine proteinases are essentially synthesised as inactive proenzymes ( zymogens ) with N -terminal propeptide regions. The activation process of these enzymes includes

910-619: The papain-like protease family are usually referred to as cysteine cathepsins—that is, the cysteine protease members of the group of proteases known as cathepsins (which includes cysteine, serine , and aspartic proteases ). In humans, there are 11 cysteine cathepsins: B , C , F , H , K , L , O , S , V , X , and W . Most cathepsins are expressed throughout the body, but some have narrower tissue distribution. Although historically known as lysosomal proteases and studied mainly for their role in protein catabolism , cysteine cathepsins have since been identified playing major roles in

945-426: The papain-like proteases. They are thought to have a shared evolutionary origin. As of 2021, the clan contained 45 families. The structure of papain was among the earliest protein structures experimentally determined by X-ray crystallography . Many papain-like protease enzymes function as monomers , though a few, such as cathepsin C (Dipeptidyl-peptidase I), are homotetramers . The mature monomer structure

980-484: The plant pathogen Xylella fastidiosa ; Cwp84 from Clostridioides difficile ; and Lpg2622 from Legionella pneumophila . The papain-like protease family includes a number of protein domains that are found in large polyproteins expressed by RNA viruses . Among the best studied viral PLPs are nidoviral papain-like protease domains from nidoviruses , particularly those from coronaviruses . These PLPs are responsible for several cleavage events that process

1015-480: The presence of endogenous protease inhibitors such as cystatins . In many RNA viruses , including significant human pathogens such as the coronaviruses SARS-CoV and SARS-CoV-2 , papain-like protease protein domains often have roles in processing of polyproteins into mature viral nonstructural proteins . Many papain-like proteases are considered potential drug targets . The MEROPS system of protease enzyme classification defines clan CA as containing

1050-405: The removal of propeptide regions, which serve a variety of functions in vivo and in vitro . The pro-region is required for the proper folding of the newly synthesised enzyme, the inactivation of the peptidase domain and stabilisation of the enzyme against denaturing at neutral to alkaline pH conditions. Amino acid residues within the pro-region mediate their membrane association, and play a role in

1085-475: The required catalytic residues cysteine, histidine, and aspartate are sometimes called the catalytic triad (similar to serine proteases ). Papain-like proteases are usually endopeptidases , but some members of the group are also, or even exclusively, exopeptidases . Some viral papain-like proteases, including those of coronaviruses , can also cleave isopeptide bonds and can function as deubiquitinases . In animals, especially in mammalian biology, members of

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1120-435: The source of papain, implying that people with latex sensitivity may be at increased risk of suffering an adverse reaction to a topical papain drug product. FDA recommended that people with concerns about using topical papain preparations contact their health care provider about discontinuing use. Papain-like protease Papain-like proteases (or papain-like (cysteine) peptidases ; abbreviated PLP or PLCP ) are

1155-406: The transport of the proenzyme to lysosomes. Among the most notable features of propeptides is their ability to inhibit the activity of their cognate enzymes and that certain propeptides exhibit high selectivity for inhibition of the peptidases from which they originate. The papain precursor protein contains 345 amino acid residues, and consists of a signal sequence (1-18), a propeptide (19-133) and

1190-470: The use of sheep anti- Crotalid toxin antibody preparations, known as CroFab and in Digibind , a similar sheep antiserum fragment, used to neutralize the cardiac medication digoxin in acute overdose situations. Papain is usually produced as a crude, dried material by collecting the latex from the fruit of the papaya tree. The latex is collected after scoring the neck of the fruit, where it may either dry on

1225-432: Was used before European contact to tenderise meat eaten in its native South America. Meat tenderisers in powder form with papain as an active component are widely sold and the culinary use of papaya peel has featured in research papers. Papain can be used to dissociate cells in the first step of cell culture preparations. A ten-minute treatment of small tissue pieces (less than 1 mm) will allow papain to begin cleaving

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