Papain Inhibitor

Papain Inhibitor peptide,(C19H29N7O6),a peptide with the sequence H-Gly-Gly-Tyr-Arg-OH,MW= 451.4,this peptide Inhibits the peptidase activity of Papain. Papain,also known as papaya proteinase I,is a cysteine protease enzyme present in papaya and mountain papaya. The mechanism by which it breaks peptide bonds involves deprotonation of Cys-25 by His-159. Asparagine-175 helps to orient the imidazole ring of His-159 to allow this deprotonation to take place. Cys-25 then performs a nucleophilic attack on the carbonyl carbon of a peptide backbone. This frees the amino terminal of the peptide,and forms a covalent acyl-enzyme intermediate. The enzyme is then deacylated by a water molecule,and releases the carboxy terminal portion of the peptide. In immunology,papain is known to cleave the Fc (crystallisable) portion of immunoglobulins (antibodies) from the Fab (antigen-binding) portion⁽¹⁾. Papain prefers to cleave at: (hydrophobic) -(Arg or Lys)- cleaves here -(not Val). Hydrophobic is Ala,Val,Leu,Ile,Phe,Trp,or Tyr⁽²⁾. Papain can be used to dissociate cells in the first step of cell culture preparations. It 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 can also be found as an ingredient in some toothpastes or mints as teeth-whitener.

Figure1  Formula of Papain Inhibitor peptide

Figure2  Structure of Papain

Ref:

1. Rawlings ND,Barrett AJ (1994). "Families of cysteine peptidases". Meth. Enzymol. 244: 461–486.

2. Lopes MC,Mascarini RC,da Silva BM,Flório FM,Basting RT (2007). "Effect of a papain-based gel for chemomechanical caries removal on dentin shear bond strength". J Dent Child (Chic) 74 (2): 93–7.

Inhibitor recognition specificity of MERS-CoV papain-like protease may differ from that of SARS-CoV.[Pubmed:25746232]

ACS Chem Biol. 2015 Jun 19;10(6):1456-65.

The Middle East Respiratory Syndrome coronavirus (MERS-CoV) papain-like protease (PLpro) blocking loop 2 (BL2) structure differs significantly from that of SARS-CoV PLpro, where it has been proven to play a crucial role in SARS-CoV PLpro inhibitor binding. Four SARS-CoV PLpro lead inhibitors were tested against MERS-CoV PLpro, none of which were effective against MERS-CoV PLpro. Structure and sequence alignments revealed that two residues, Y269 and Q270, responsible for inhibitor binding to SARS-CoV PLpro, were replaced by T274 and A275 in MERS-CoV PLpro, making critical binding interactions difficult to form for similar types of inhibitors. High-throughput screening (HTS) of 25000 compounds against both PLpro enzymes identified a small fragment-like noncovalent dual inhibitor. Mode of inhibition studies by enzyme kinetics and competition surface plasmon resonance (SPR) analyses suggested that this compound acts as a competitive inhibitor with an IC50 of 6 muM against MERS-CoV PLpro, indicating that it binds to the active site, whereas it acts as an allosteric inhibitor against SARS-CoV PLpro with an IC50 of 11 muM. These results raised the possibility that inhibitor recognition specificity of MERS-CoV PLpro may differ from that of SARS-CoV PLpro. In addition, inhibitory activity of this compound was selective for SARS-CoV and MERS-CoV PLpro enzymes over two human homologues, the ubiquitin C-terminal hydrolases 1 and 3 (hUCH-L1 and hUCH-L3).

Isolation and purification of a papain inhibitor from Egyptian genotypes of barley seeds and its in vitro and in vivo effects on the cowpea bruchid, Callosobruchus maculatus (F.).[Pubmed:25752426]

Pestic Biochem Physiol. 2015 Feb;118:26-32.

The cysteine inhibitors that are known as cystatin have been identified and characterized from several plant species. In the current study, 44 barley (Hordeum vulgare) genotypes including 3 varieties and 41 promising lines were screened for their potential as protease inhibitors. The barley genotypes showed low inhibitory activity against trypsin and chymotrypsin enzymes with a mean of 4.15 TIU/mg protein and 4.40 CIU/mg protein. The barley variety, Giza 123, showed strong Papain Inhibitory activity of 97.09 PIU/mg proteins and was subjected for further purification studies using ammonium sulfate fractionation and DEAE-Sephadex A-25 column. Barley purified proteins showed two bands on SDS-PAGE corresponding to a molecular mass of 12.4-54.8 kDa. The purified barley PI was found to be stable at a temperature below 80 degrees C and at a wide range of pH from 2 to 12. Barley PI was found to have higher potential inhibitory activity against papain enzyme compared to the standard Papain Inhibitor, E-64 with an IC50 value of 21.04 microg/ml and 25.62 microg/ml for barley PI and E-64, respectively. The kinetic analysis revealed a non-competitive type of inhibition with a Ki value of 1.95 x 10(-3 )microM. The antimetabolic effect of barley PI was evaluated against C. maculatus by incorporating the F30-60 protein of the purified inhibitor into the artificial diet using artificial seeds. Barley PI significantly prolonged the development of C. maculatus in proportion to PI concentration. Barley PI significantly increased the mortality of C. maculatus and caused a significant reduction in its fecundity. On the other hand, barley PI seemed to have non-significant effects on the adult longevity and the adult dry weight. The in vitro and in vivo results proved the efficiency of the Papain Inhibitory protein isolated from barley as a tool for managing the cowpea bruchid, C. maculatus.

An Unusual Member of the Papain Superfamily: Mapping the Catalytic Cleft of the Marasmius oreades agglutinin (MOA) with a Caspase Inhibitor.[Pubmed:26901797]

PLoS One. 2016 Feb 22;11(2):e0149407.

Papain-like cysteine proteases (PLCPs) constitute the largest group of thiol-based protein degrading enzymes and are characterized by a highly conserved fold. They are found in bacteria, viruses, plants and animals and involved in a number of physiological and pathological processes, parasitic infections and host defense, making them interesting targets for drug design. The Marasmius oreades agglutinin (MOA) is a blood group B-specific fungal chimerolectin with calcium-dependent proteolytic activity. The proteolytic domain of MOA presents a unique structural arrangement, yet mimicking the main structural elements in known PLCPs. Here we present the X-ray crystal structure of MOA in complex with Z-VAD-fmk, an irreversible caspase inhibitor known to cross-react with PLCPs. The structural data allow modeling of the substrate binding geometry and mapping of the fundamental enzyme-substrate interactions. The new information consolidates MOA as a new, yet strongly atypical member of the papain superfamily. The reported complex is the first published structure of a PLCP in complex with the well characterized caspase inhibitor Z-VAD-fmk.

Papain and its inhibitor E-64 reduce camelid semen viscosity without impairing sperm function and improve post-thaw motility rates.[Pubmed:27156102]

Reprod Fertil Dev. 2017 Jun;29(6):1107-1114.

In camelids, the development of assisted reproductive technologies is impaired by the viscous nature of the semen. The protease papain has shown promise in reducing viscosity, although its effect on sperm integrity is unknown. The present study determined the optimal papain concentration and exposure time to reduce seminal plasma viscosity and investigated the effect of papain and its inhibitor E-64 on sperm function and cryopreservation in alpacas. Papain (0.1mg mL(-1), 20min, 37 degrees C) eliminated alpaca semen viscosity while maintaining sperm motility, viability, acrosome integrity and DNA integrity. Furthermore E-64 (10 microM at 37 degrees C for 5min after 20min papain) inhibited the papain without impairing sperm function. Cryopreserved, papain-treated alpaca spermatozoa exhibited higher total motility rates after chilling and 0 and 1h after thawing compared with control (untreated) samples. Papain treatment, followed by inhibition of papain with E-64, is effective in reducing alpaca seminal plasma viscosity without impairing sperm integrity and improves post-thaw motility rates of cryopreserved alpaca spermatozoa. The use of the combination of papain and E-64 to eliminate the viscous component of camelid semen may aid the development of assisted reproductive technologies in camelids.