Effects of mechanical wounding on Carica papaya cysteine endopeptidases accumulation and activity

The front line of defence: a meta-analysis of apoplastic proteases in plant immunity

Secreted proteases act at the front line of defence and play pivotal roles in disease resistance. However, the criteria for apoplastic immune proteases are not always defined and followed. Here, we critically reviewed 46 apoplastic proteases that function in plant defence. We found that most apoplastic immune proteases are induced upon infection, and 17 proteases are genetically required for the immune response. Proteolytic activity has been confirmed for most of the proteases but is rarely shown to be required for biological function, and the apoplastic location of proteases can be subjective and dynamic. Pathogen-derived inhibitors have only been described for cysteine and serine proteases, and the selection pressure acting on immune proteases is rarely investigated. We discuss six different mechanisms by which these proteases mediate plant immunity and summarize the challenges for future research.

An Aphid-Secreted Salivary Protease Activates Plant Defense in Phloem

Recent studies have reported that aphids facilitate their colonization of host plants by secreting salivary proteins into host tissues during their initial probing and feeding. Some of these salivary proteins elicit plant defenses, but the molecular and biochemical mechanisms that underlie the activation of phloem-localized resistance remain poorly understood. The aphid Myzus persicae, which is a generalized phloem-sucking pest, encompasses a number of lineages that are associated with and adapted to specific host plant species. The current study found that a cysteine protease Cathepsin B3 (CathB3), and the associated gene CathB3, was upregulated in the salivary glands and saliva of aphids from a non-tobacco-adapted (NTA) aphid lineage, when compared to those of a tobacco-adapted lineage. Furthermore, the knockdown of CathB3 improved the performance of NTA lineages on tobacco, and the propeptide domain of CathB3 was found to bind to tobacco cytoplasmic kinase ENHANCED DISEASE RESISTANCE 1-like (EDR1-like), which triggers the accumulation of reactive oxygen species in tobacco phloem, thereby suppressing both phloem feeding and colonization by NTA lineages. These findings reveal a novel function for a cathepsin-type protease in aphid saliva that elicits effective host plant defenses and warranted the theory of host specialization for generalist aphids.

One-step recovery of latex papain from Carica papaya using three phase partitioning and its use as milk-clotting and meat-tenderizing agent

Three Phase Partitioning (TPP) system as an elegant non-chromatographic and bulk separation method was successfully applied for the extraction and recovery of papain from the latex of Carica papaya. The optimized parameters of TPP allowed achieving a purification fold of 11.45 and activity recovery of 134% with 40% (NH₄)₂SO₄, 1.0:0.75 ratio of crude extract: t-BuOH at pH and temperature of 6.0 and 25 °C, respectively. The recovered papain had a molecular weight of 23.2 kDa and revealed maximum activity at pH 6.0 and temperature of 50 °C. The maximum values of Km and Vmax parameters were 10.83 mg mL^-1 and 33.33 U mL^-1, respectively. The protease with 4 isoforms was stable at 40-80 °C and a pH range of 6.0-7.5 against numerous metal ions and none of them inactivated the recovered protease. Moreover, 10 mM Ca²⁺ improved 2-folds the activity and half-life of the protease at temperatures from 30 to 50 °C. The milk-clotting activity tests revealed high stability of latex papain at storage, namely at -20 °C compared to 4 °C and 25 °C for up than 5 weeks. As a meat tenderizing agent, it showed promising role under different treatments by improving the texture of tough meat. The findings indicated that one-step TPP system is a simple, quick, economical and very attractive process for fast recovery of latex papain compared to other proposed protocols.

A Conserved Microbial Motif 'Traps' Protease Activation in Host Immunity

A recent study (Misas-Villamil et al., Nat. Commun., 2019) reveals that Pit2, an apoplastic effector of the corn smut fungus Ustilago maydis, contains an embedded motif of 14 amino acids that binds to and inhibits plant cysteine proteases, thereby modulating host immunity. Intriguingly, the inhibitory motif acts by mimicking the protease substrate and is conserved across microbial kingdoms.

Papain-like cysteine proteases as hubs in plant immunity

902 I. 902 II. 903 III. 903 IV. 903 V. 905 VI. 905 VII. 905 906 References 906 SUMMARY: Plants deploy a sophisticated immune system to cope with different microbial pathogens and other invaders. Recent research provides an increasing body of evidence for papain-like cysteine proteases (PLCPs) being central hubs in plant immunity. PLCPs are required for full resistance of plants to various pathogens. At the same time, PLCPs are targeted by secreted pathogen effectors to suppress immune responses. Consequently, they are subject to a co-evolutionary host-pathogen arms race. When activated, PLCPs induce a broad spectrum of defense responses including plant cell death. While the important role of PLCPs in plant immunity has become more evident, it remains largely elusive how these enzymes are activated and which signaling pathways are triggered to orchestrate different downstream responses.

Autolysis control and structural changes of purified ficin from Iranian fig latex with synthetic inhibitors

The fig's ficin is a cysteine endoproteolytic enzyme, which plays fundamental roles in many plant physiological processes, and has many applications in different industries such as pharmaceutical and food. In this work, we report the inhibition and activation of autolysis and structural changes associated with reaction of ficin with iodoacetamide and tetrathionate using high-performance liquid chromatography (HPLC), ultra filtration membrane, and dynamic light scattering (DLS) methods. The ficin structural changes were also determined using UV-absorption, circular dichroism (CD), fluorescence spectroscopy, and differential scanning calorimetry (DSC) techniques. These techniques demonstrated that iodoacetamide completely inhibited ficin autolysis, which was irreversible. However, tetrathionate partially and reversibility inhibited its autolysis. The ficin structural changes with two synthetic inhibitors were associated with secondary structural changes related to decreased alpha-helix and increased beta sheet and random coil conformations, contributing to its aggregation.

A novel form of ficin from Ficus carica latex: Purification and characterization

A novel ficin form, named ficin E, was purified from fig tree latex by a combination of cation-exchange chromatography on SP-Sepharose Fast Flow, Thiopropyl Sepharose 4B and fplc-gel filtration chromatography. The new ficin appeared not to be sensitive to thiol derivatization by a polyethylene glycol derivative, allowing its purification. The protease is homogeneous according to PAGE, SDS-PAGE, mass spectrometry, N-terminal micro-sequencing analyses and E-64 active site titration. N-terminal sequencing of the first ten residues has shown high identity with the other known ficin (iso)forms. The molecular weight was found to be (24,294±10)Da by mass spectrometry, a lower value than the apparent molecular weight observed on SDS-PAGE, around 27 kDa. Far-UV CD data revealed a secondary structure content of 22% α-helix and 26% β-sheet. The protein is not glycosylated as shown by carbohydrate analysis. pH and temperature measurements indicated maxima activity at pH 6.0 and 50 °C, respectively. Preliminary pH stability analyses have shown that the protease conserved its compact structure in slightly acidic, neutral and alkaline media but at acidic pH (<3), the formation of some relaxed or molten state was evidenced by 8-anilino-1-naphtalenesulfonic acid binding characteristics. Comparison with the known ficins A, B, C, D1 and D2 (iso)forms revealed that ficin E showed activity profile that looked like ficin A against two chromogenic substrates while it resembled ficins D1 and D2 against three fluorogenic substrates. Enzymatic activity of ficin E was not affected by Mg(2+), Ca(2+) and Mn(2+) at a concentration up to 10mM. However, the activity was completely suppressed by Zn(2+) at a concentration of 1mM. Inhibitory activity measurements clearly identified the enzyme as a cysteine protease, being unaffected by synthetic (Pefabloc SC, benzamidine) and by natural proteinaceous (aprotinin) serine proteases inhibitors, by aspartic proteases inhibitors (pepstatin A) and by metallo-proteases inhibitors (EDTA, EGTA). Surprisingly, it was well affected by the metallo-protease inhibitor o-phenanthroline. The enzymatic activity was however completely blocked by cysteine proteases inhibitors (E-64, iodoacetamide), by thiol-blocking compounds (HgCl2) and by cysteine/serine proteases inhibitors (TLCK and TPCK). This is a novel ficin form according to peptide mass fingerprint analysis, specific amidase activity, SDS-PAGE and PAGE electrophoretic mobility, N-terminal sequencing and unproneness to thiol pegylation.

A current overview of the Papaya meleira virus, an unusual plant virus

Papaya meleira virus (PMeV) is the causal agent of papaya sticky disease, which is characterized by a spontaneous exudation of fluid and aqueous latex from the papaya fruit and leaves. The latex oxidizes after atmospheric exposure, resulting in a sticky feature on the fruit from which the name of the disease originates. PMeV is an isometric virus particle with a double-stranded RNA (dsRNA) genome of approximately 12 Kb. Unusual for a plant virus, PMeV particles are localized on and linked to the polymers present in the latex. The ability of the PMeV to inhabit such a hostile environment demonstrates an intriguing interaction of the virus with the papaya. A hypersensitivity response is triggered against PMeV infection, and there is a reduction in the proteolytic activity of papaya latex during sticky disease. In papaya leaf tissues, stress responsive proteins, mostly calreticulin and proteasome-related proteins, are up regulated and proteins related to metabolism are down-regulated. Additionally, PMeV modifies the transcription of several miRNAs involved in the modulation of genes related to the ubiquitin-proteasome system. Until now, no PMeV resistant papaya genotype has been identified and roguing is the only viral control strategy available. However, a single inoculation of papaya plants with PMeV dsRNA delayed the progress of viral infection.

Relationship between fermented papaya preparation supplementation, erythrocyte integrity and antioxidant status in pre-diabetics

Erythrocytes and their membranes are favorable models to study the relationship between diabetes and susceptibility of erythrocytes to oxidative stress damage. The recommendation for the use of fermented papaya preparation (FPP) as a functional food for dietary management of type 2 diabetes was evaluated by assessing its effect on the human antioxidant status and erythrocyte integrity on a multi-ethnical pre-diabetic population. The in vivo effect of FPP was compared with its in vitro free radical scavenging potentials. FPP exhibited potent in vitro free radical scavenging activities thought to be attributed to residual phenolic or flavonoid compounds. Low doses of FPP significantly reduced the susceptibility of human erythrocytes to undergo free radical-induced hemolysis. The intake of 6g FPP/day for a period of 14weeks was observed to significantly reduce the rate of hemolysis and accumulation of protein carbonyls in the blood plasma of pre-diabetics. That FPP consumption on a daily basis can strengthen the antioxidant defense system in vivo was clearly demonstrated by the marked increase of total antioxidant status in the FPP-supplemented pre-diabetics. That FPP maintains the integrity of erythrocytes could benefit the strategies to improve the quality of future blood products.

Label-free quantitative proteomics reveals differentially regulated proteins in the latex of sticky diseased Carica papaya L. plants

Papaya meleira virus (PMeV) is so far the only described laticifer-infecting virus, the causal agent of papaya (Carica papaya L.) sticky disease. The effects of PMeV on the laticifers' regulatory network were addressed here through the proteomic analysis of papaya latex. Using both 1-DE- and 1D-LC-ESI-MS/MS, 160 unique papaya latex proteins were identified, representing 122 new proteins in the latex of this plant. Quantitative analysis by normalized spectral counting revealed 10 down-regulated proteins in the latex of diseased plants, 9 cysteine proteases (chymopapain) and 1 latex serine proteinase inhibitor. A repression of papaya latex proteolytic activity during PMeV infection was hypothesized. This was further confirmed by enzymatic assays that showed a reduction of cysteine-protease-associated proteolytic activity in the diseased papaya latex. These findings are discussed in the context of plant responses against pathogens and may greatly contribute to understand the roles of laticifers in plant stress responses.

Selective and reversible thiol-pegylation, an effective approach for purification and characterization of five fully active ficin (iso)forms from Ficus carica latex

The latex of Ficus carica constitutes an important source of many proteolytic components known under the general term of ficin (EC 3.4.22.3) which belongs to the cysteine proteases of the papain family. So far, no data on the purification and characterization of individual forms of these proteases are available. An effective strategy was used to fractionate and purify to homogeneity five ficin forms, designated A, B, C, D1 and D2 according to their sequence of elution from a cation-exchange chromatographic support. Following rapid fractionation on a SP-Sepharose Fast Flow column, the different ficin forms were chemically modified by a specific and reversible monomethoxypolyethylene glycol (mPEG) reagent. In comparison with their un-derivatized counterparts, the mPEG-protein derivatives behaved differently on the ion-exchanger, allowing us for the first time to obtain five highly purified ficin molecular species titrating 1mol of thiol group per mole of enzyme. The purified ficins were characterized by de novo peptide sequencing and peptide mass fingerprinting analyzes, using mass spectrometry. Circular dichroism measurements indicated that all five ficins were highly structured, both in term of secondary and tertiary structure. Furthermore, analysis of far-UV CD spectra allowed calculation of their secondary structural content. Both these data and the molecular masses determined by MS reinforce the view that the enzymes belong to the family of papain-like proteases. The five ficin forms also displayed different specific amidase activities against small synthetic substrates like dl-BAPNA and Boc-Ala-Ala-Gly-pNA, suggesting some differences in their active site organization. Enzymatic activity of the five ficin forms was completely inhibited by specific cysteine and cysteine/serine proteases inhibitors but was unaffected by specific serine, aspartic and metallo proteases inhibitors.

Purification and in situ immobilization of papain with aqueous two-phase system

Papain was purified from spray-dried Carica papaya latex using aqueous two-phase system (ATPS). Then it was recovered from PEG phase by in situ immobilization or preparing cross-linked enzyme aggregates (CLEAs). The Plackett-Burman design and the central composite design (CCD) together with the response surface methodology (RSM) were used to optimize the APTS processes. The highly purified papain (96–100%) was achieved under the optimized conditions: 40% (w/w) 15 mg/ml enzyme solution, 14.33–17.65% (w/w) PEG 6000, 14.27–14.42% (w/w) NaH₂PO₄/K₂HPO₄ and pH 5.77–6.30 at 20°C. An in situ enzyme immobilization approach, carried out by directly dispersing aminated supports and chitosan beads into the PEG phase, was investigated to recover papain, in which a high immobilization yield (>90%) and activity recovery (>40%) was obtained. Moreover, CLEAs were successfully used in recovering papain from PEG phase with a hydrolytic activity hundreds times higher than the carrier-bound immobilized papain.

Purification and characterization of a wound-inducible thaumatin-like protein from the latex of Carica papaya

A 22.137 kDa protein constituent of fresh latex was isolated both from the latex of regularly damaged papaya trees and from a commercially available papain preparation. The protein was purified up to apparent homogeneity and was shown to be absent in the latex of papaya trees that had never been previously mechanically injured. This suggests that the protein belongs to pathogenesis-related protein family, as expected for several other protein constituents of papaya latex. The protein was identified as a thaumatin-like protein (class 5 of the pathogenesis-related proteins) on the basis of its partial amino acid sequence. By sequence analysis of the Carica genome, three different forms of thaumatin-like protein were identified, where the latex constituent belongs to a well-known form, allowing the molecular modeling of its spatial structure. The papaya latex thaumatin-like protein was further characterized. The protein appears to be stable in the pH interval from 2 to 10 and resistant to chemical denaturation by guanidium chloride, with a DeltaG(water)(0) of 15.2 kcal/mol and to proteolysis by the four papaya cysteine proteinases. The physiological role of this protein is discussed.

Effects of the Papaya meleira virus on papaya latex structure and composition

Spontaneous latex exudation is the main symptom of papaya sticky (meleira) disease caused by the Papaya meleira virus (PMeV), a double-stranded RNA (dsRNA) virus. This paper describes different effects of PMeV on papaya latex. Latex samples were subjected to different histochemical tests to evaluate their chemical composition. Additionally, the integrity of the latex particles was assessed by transmission and scanning electron microscopy analysis. Biochemical and micro- and macro-element measurements were performed. PMeV dsRNA extraction was performed to evaluate the interaction of the virus with the latex particles. Sticky diseased latex was positive for alkaloid biosynthesis and showed an accumulation of calcium oxalate crystals. PMeV also increased H(2)O(2) synthesis within sticky diseased laticifers. The protein, sugar and water levels were altered, probably due to chemical changes. The morphology of the latex particles was further altered; PMeV particles seemed to be bound to the latex particles. The alkaloid and H(2)O(2) biosynthesis in the papaya laticifers indicate a papaya defense response against PMeV. However, such efforts failed, as the virus affected the plant latex. The effects described here suggest some advantages of the infection process, including facilitating the movement of the virus within the papaya plant.

Papain-like cysteine proteases: key players at molecular battlefields employed by both plants and their invaders

Papain-like cysteine proteases (PLCPs) play crucial roles in plant-pathogen/pest interactions. During these parasitic interactions, PLCPs act on non-self substrates, provoking the selection of counteracting inhibitors and other means to evade proteolysis. We review examples of PLCPs acting on molecular battlefields in the extracellular space, plant cytoplasm and herbivore gut. Examples are maize Mir1 (Maize inbred resistance 1), tomato Rcr3 (Required for Cladosporium resistance-3), Pseudomonas AvrRpt2 and AurPphB, insect DvCAL1 (Diabrotica virgifera cathepsin L-like protease-1) and nematode MiCpl1 (Meloidogyne incognita cathepsin L-like protease 1). The data suggest that PLCPs cleave specific proteins and that their translocation, activation and inhibition of PLCPs are tightly regulated.