Purification of a novel type of SDS-dependent protease in maize using a monoclonal antibody

The lysosomal function of progranulin, a guardian against neurodegeneration

Progranulin (PGRN), encoded by the GRN gene in humans, is a secreted growth factor implicated in a multitude of processes ranging from regulation of inflammation to wound healing and tumorigenesis. The clinical importance of PGRN became especially evident in 2006, when heterozygous mutations in the GRN gene, resulting in haploinsufficiency, were found to be one of the main causes of frontotemporal lobar degeneration (FTLD). FTLD is a clinically heterogenous disease that results in the progressive atrophy of the frontal and temporal lobes of the brain. Despite significant research, the exact function of PGRN and its mechanistic relationship to FTLD remain unclear. However, growing evidence suggests a role for PGRN in the lysosome-most striking being that homozygous GRN mutation leads to neuronal ceroid lipofuscinosis, a lysosomal storage disease. Since this discovery, several links between PGRN and the lysosome have been established, including the existence of two independent lysosomal trafficking pathways, intralysosomal processing of PGRN into discrete functional peptides, and direct and indirect regulation of lysosomal hydrolases. Here, we summarize the cellular functions of PGRN, its roles in the nervous system, and its link to multiple neurodegenerative diseases, with a particular focus dedicated to recent lysosome-related mechanistic developments.

C1A cysteine protease-cystatin interactions in leaf senescence

Senescence-associated proteolysis in plants is a crucial process to relocalize nutrients from leaves to growing or storage tissues. The massive net degradation of proteins involves broad metabolic networks, different subcellular compartments, and several types of proteases and regulators. C1A cysteine proteases, grouped as cathepsin L-, B-, H-, and F-like according to their gene structures and phylogenetic relationships, are the most abundant enzymes responsible for the proteolytic activity during leaf senescence. Besides, cystatins as specific modulators of C1A peptidase activities exert a complex regulatory role in this physiological process. This overview article covers the most recent information on C1A proteases in leaf senescence in different plant species. Particularly, it is focussed on barley, as the unique species where the whole gene family members of C1A cysteine proteases and cystatins have been analysed.

A structural biology approach to understand human lymphatic filarial infection

The presence of aspartic protease inhibitor in filarial parasite Brugia malayi (Bm-Aspin) makes it interesting to study because of the fact that the filarial parasite never encounters the host digestive system. Here, the aspartic protease inhibition kinetics of Bm-Aspin and its NMR structural characteristics have been investigated. The overall aim of this study is to explain the inhibition and binding properties of Bm-Aspin from its structural point of view. UV-spectroscopy and multi-dimensional NMR are the experiments that have been performed to understand the kinetic and structural properties of Bm-Aspin respectively. The human aspartic proteases that are considered for this study are pepsin, renin, cathepsin-E and cathepsin-D. The results of this analysis performed with the specific substrate [Phe-Ala-Ala-Phe (4-NO2)-Phe-Val-Leu (4-pyridylmethyl) ester] against aspartic proteases suggest that Bm-Aspin inhibits the activities of all four human aspartic proteases. The kinetics studies indicate that Bm-Aspin follows a competitive mode of inhibition for pepsin and cathepsin-E, non-competitive for renin and mixed mode for cathepsin-D. The triple resonance NMR experiments on Bm-Aspin suggested the feasibility of carrying out NMR studies to obtain its solution structure. The NMR titration studies on the interactions of Bm-Aspin with the proteases indicate that it undergoes fast-exchange phenomena among themselves. In addition to this, the chemical shift perturbations for some of the residues of Bm-Aspin observed from (15)N-HSQC spectra upon the addition of saturated amounts of aspartic proteases suggest the binding between Bm-Aspin and human aspartic proteases. They also provide information on the variations in the intensities and mode of binding between the proteases duly corroborating with the results from the protease inhibition assay method.

Apoplastic immunity and its suppression by filamentous plant pathogens

Microbial plant pathogens have evolved a variety of strategies to enter plant hosts and cause disease. In particular, biotrophic pathogens, which parasitize living plant tissue, establish sophisticated interactions in which they modulate the plant's metabolism to their own good. The prime decision, whether or not a pathogen can accommodate itself in its host tissue, is made during the initial phase of infection. At this stage, the plant immune system recognizes conserved molecular patterns of the invading microbe, which initiate a set of basal immune responses. Induced plant defense proteins, toxic compounds and antimicrobial proteins encounter a broad arsenal of pathogen-derived virulence factors that aim to disarm host immunity. Crucial regulatory processes and protein-protein interactions take place in the apoplast, that is, intercellular spaces, plant cell walls and defined host-pathogen interfaces which are formed between the plant cytoplasm and the specialized infection structures of many biotrophic pathogens. This article aims to provide an insight into the most important principles and components of apoplastic plant immunity and its modulation by filamentous microbial pathogens.

C1A cysteine-proteases and their inhibitors in plants

Plant cysteine-proteases (CysProt) represent a well-characterized type of proteolytic enzymes that fulfill tightly regulated physiological functions (senescence and seed germination among others) and defense roles. This article is focused on the group of papain-proteases C1A (family C1, clan CA) and their inhibitors, phytocystatins (PhyCys). In particular, the protease-inhibitor interaction and their mutual participation in specific pathways throughout the plant's life are reviewed. C1A CysProt and PhyCys have been molecularly characterized, and comparative sequence analyses have identified consensus functional motifs. A correlation can be established between the number of identified CysProt and PhyCys in angiosperms. Thus, evolutionary forces may have determined a control role of cystatins on both endogenous and pest-exogenous proteases in these species. Tagging the proteases and inhibitors with fluorescence proteins revealed common patterns of subcellular localization in the endoplasmic reticulum-Golgi network in transiently transformed onion epidermal cells. Further in vivo interactions were demonstrated by bimolecular fluorescent complementation, suggesting their participation in the same physiological processes.

Post-translational regulation and trafficking of the granulin-containing protease RD21 of Arabidopsis thaliana

RD21-like proteases are ubiquitous, plant-specific papain-like proteases typified by carrying a C-terminal granulin domain. RD21-like proteases are involved in immunity and associated with senescence and various types of biotic and abiotic stresses. Here, we interrogated Arabidopsis RD21 regulation and trafficking by site-directed mutagenesis, agroinfiltration, western blotting, protease activity profiling and protein degradation. Using an introduced N-glycan sensor, deglycosylation experiments and glyco-engineered N. benthamiana plants, we show that RD21 passes through the Golgi where it becomes fucosylated. Our studies demonstrate that RD21 is regulated at three post-translational levels. Prodomain removal is not blocked in the catalytic Cys mutant, indicating that RD21 is activated by a proteolytic cascade. However, RD21 activation in Arabidopsis does not require vacuolar processing enzymes (VPEs) or aleurain-like protease AALP. In contrast, granulin domain removal requires the catalytic Cys and His residues and is therefore autocatalytic. Furthermore, SDS can (re-)activate latent RD21 in Arabidopsis leaf extracts, indicating the existence of a third layer of post-translational regulation, possibly mediated by endogenous inhibitors. RD21 causes a dominant protease activity in Arabidopsis leaf extracts, responsible for SDS-induced proteome degradation.

Partial purification and characterisation of cysteine protease in wheat germ

BACKGROUND

Proteases have become an essential part of the modern food and feed industry, being incorporated in a large and diversified range of products for human and animal consumption. The objective of this study was to purify and characterise a protease from wheat germ.

RESULTS

After purification a single protease of molecular weight 61-63 kDa (determined by sodium dodecyl sulfate polyacrylamide gel electrophoresis) was obtained. The purified protease had optimal activity at 50 °C and maintained its activity completely after incubation at 30 °C for 30 min, while over 47% of the activity was lost after incubation at 80 °C for 30 min. The purified protease had optimal activity and maintained maximum stability at pH 5.5, while the activity decreased after incubation for 30 min at other pH values. The protease was inhibited by Mg(2+), Mn(2+), Ba(2+) and iodoacetic acid and stimulated by Li(+), Ca(2+), Cu(2+), β-mercaptoethanol and dithiothreitol, while Zn(2+), L-cysteine and glutathione had no significant effect on its activity. At pH 5.5 the enzyme had a K(m) of 0.562 mg mL(-1) with casein as substrate and showed higher affinity to casein than to bovine serum albumin, ovalbumin and gelatin.

CONCLUSION

The purified enzyme from wheat germ was identified as a cysteine protease.

SDS-dependent proteases induced by ABA and its relation to Rubisco and Rubisco activase contents in rice leaves

Protease activities and its relation to the contents of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) and Rubisco activase were investigated in detached leaves of rice (Oryza sativa L.) floated on the solutions containing abscisic acid (ABA) or benzyladenine (BA). Rubisco and Rubisco activase contents were decreased during the time course and the decreases were enhanced by ABA and suppressed by BA. The decrease in Rubisco activase was faster than that in Rubisco. SDS-dependent protease activities at 50-70 kDa (rice SDS-dependent protease: RSP) analyzed by the gelatin containing PAGE were significantly enhanced by ABA. RSPs were also increased in attached leaves during senescence. RSPs had the pH optimum of 5.5, suggesting that RSPs are vacuolar protease. Both decrease in Rubisco and Rubisco activase contents and increase in RSPs activities were suppressed by cycloheximide. These findings indicate that the activities of RSPs are well correlated with the decrease in these protein contents. Immunoblotting analysis showed that Rubisco in the leaf extracts was completely degraded by 5h at pH 5.5 with SDS where it was optimal condition for RSPs. However, the degradation of Rubisco did not proceed at pH 7.5 without SDS where it is near physiological condition for stromal proteins. Rubisco activase was degraded at similar rate under both conditions. These results suggest that RSPs can functions in a senescence related degradation system of chloroplast protein in rice leaves. Rubisco activase would be more susceptible to proteolysis than Rubisco under physiological condition and this could affect the contents of these proteins in leaves.

Characterization of cysteine protease induced by oxidative stress in cells of Chlamydomonas sp. strain W80

Unlike known Chlamydomonas species, Chlamydomonas sp. strain W80, which was isolated from seawater, shows tolerance to salt and cadmium. In this study, we purified and characterized cysteine protease from Chlamydomonas sp. strain W80 cells and also investigated their response to oxidative stress. The protease was purified 2760-fold with a yield of 2.6% by five steps of successive chromatography. This protease had a pH optimum of 8.0 and was specific only for tert-butoxycarbonyl (Boc)-Leu-Arg-Arg-4-methylcoumaryl-7-amide (MCA) (Boc-LRR-MCA) and Boc-Val-Leu-Lys-MCA as substrates among eight fluorogenic peptides tested. The K(m) value was estimated to be 44.4 microM for Boc-LRR-MCA. The molecular weight of the protease was determined to be approximately 102 kDa by Superdex 200 gel filtration and 60 kDa by SDS-PAGE, suggesting that this enzyme is a dimer. This enzyme was inhibited by the cysteine protease inhibitors leupeptin and N-ethylmaleimide but neither inhibited by phenylmethylsulfonyl fluoride or ethylenediaminetetraacetic acid nor activated by metal cations. These findings indicate that this enzyme is likely a cysteine protease. When strain W80 was grown under oxidative stress in the presence of methyl viologen and cadmium chloride, cysteine protease activity was about 30-90% higher than normal, whereas no changes were observed in carbon enrichment or senescence. It is likely that this protease is upregulated in response to oxidative stress and plays a role in the maintenance of cell metabolism under oxidative stress conditions.

A slow maturation of a cysteine protease with a granulin domain in the vacuoles of senescing Arabidopsis leaves

Arabidopsis RD21 is a cysteine protease of the papain family. Unlike other members of the papain family, RD21 has a C-terminal extension sequence composed of two domains, a 2-kD proline-rich domain and a 10-kD domain homologous to animal epithelin/granulin family proteins. The RD21 protein was accumulated as 38- and 33-kD proteins in Arabidopsis leaves. An immunoblot showed that the 38-kD protein had the granulin domain, whereas the 33-kD protein did not. A pulse-chase experiment with Bright-Yellow 2 transformant cells expressing RD21 showed that RD21 was synthesized as a 57-kD precursor and was then slowly processed to make the 33-kD mature protein via the 38-kD intermediate. After a 12-h chase, the 38-kD intermediate was still detected in the cells. These results indicate that the N-terminal propeptide was first removed from the 57-kD precursor, and the C-terminal granulin domain was then slowly removed to yield the 33-kD mature protein. Subcellular fractionation of the Bright-Yellow 2 transformant showed that the intermediate and mature forms of RD21 were localized in the vacuoles. Under the acidic conditions of the vacuolar interior, the intermediate was found to be easily aggregated. The intermediate and the mature protein were accumulated in association with leaf senescence. Taken together, these results indicate that the intermediate of RD21 was accumulated in the vacuoles as an aggregate, and then slowly matured to make a soluble protease by removing the granulin domain during leaf senescence.

Isolation of the protease component of maize cysteine protease-cystatin complex: release of cystatin is not crucial for the activation of the cysteine protease

The maize cysteine protease complex, which required SDS for its activation in vitro, is a 179 kDa trimeric complex (P-I)3 of a cysteine protease (P) [EC 3.4.22] and a cysteine protease inhibitor (I), cystatin [Yamada et al. (1998) Plant Cell Physiol. 39: 106, Yamada et al. (2000) Plant Cell Physiol. 41: 185]. Here, we show the mechanism of the SDS-dependent activation of the trimeric (P-I) complex and stabilization of the activated protease by its specific substrates. The cystatin-free cysteine protease isolated by preparative SDS-PAGE was still specifically activated by SDS, and its profile of SDS-dependency was exactly the same as that of the trimeric (P-I) complex. It is, therefore, evident that an SDS-dependent conformational change of the protease itself, rather than the release of cystatin from the complex, is crucial for the activation. Pre-treatment analysis with SDS revealed that SDS was required for the initiation of the activation of the trimeric (P-I) complex. Furthermore, we found that once the protease was activated, if there was no substrate, it was rapidly inactivated under optimum conditions of proteolysis, and showed that such inactivation was not due to autolysis of the protease. In contrast, addition of specific substrates prevented the inactivation, and thus we presumed that the activity of the cysteine protease is regulated by both activation by conformational change and rapid inactivation after consumption of substrates.

Protease activity of CND41, a chloroplast nucleoid DNA-binding protein, isolated from cultured tobacco cells

CND41 is a 41 kDa DNA-binding protein isolated from chloroplast nucleoids of cultured tobacco cells. The presence of the active domain of aspartic protease in the deduced amino acid sequence of CND41 suggests that it has proteolytic activity. To confirm this, CND41 was highly purified from cultured tobacco cells and its proteolytic activity was characterized with fluorescein isothiocyanate-labeled hemoglobin as the substrate. The purified CND41 had strong proteolytic activity at an acidic pH (pH 2-4). This activity was inhibited by various chemicals, including the nucleoside triphosphates, NADPH, Fe(3+) and sodium dodecyl sulfate.