Specific inhibition of mature fungal serine proteinases and metalloproteinases by their propeptides

Extracellular proteases from halophiles: diversity and application challenges

Halophilic extracellular proteases offer promising application in various fields. Information on these prominent proteins including the synthesizing organisms, biochemical properties, domain organisation, purification, and application challenges has never been covered in recent reviews. Although extracellular proteases from bacteria pioneered the study of proteases in halophiles, progress is being made in proteases from halophilic archaea. Recent advances in extracellular proteases from archaea revealed that archaeal proteases are more robust and applicable. Extracellular proteases are composed of domains that determine their mechanisms of action. The intriguing domain structure of halophilic extracellular proteases consists of N-terminal domain, catalytic domain, and C-terminal extension. The role of C-terminal domains varies among different organisms. A high diversity of C-terminal domains would endow the proteases with diverse functions. With the development of genomics, culture-independent methods involving heterologous expression, affinity chromatography, and in vitro refolding are deployed with few challenges on purification and presenting novel research opportunities. Halophilic extracellular proteases have demonstrated remarkable potentials in industries such as detergent, leather, peptide synthesis, and biodegradation, with desirable properties and ability to withstand harsh industrial processes. KEY POINTS: • Halophilic extracellular proteases have robust properties suitable for applications. • A high diversity of C-terminal domains may endow proteases with diverse properties. • Novel protease extraction methods present novel application opportunities.

Effector proteins of Rhizophagus proliferus: conserved protein domains may play a role in host-specific interaction with different plant species

Arbuscular mycorrhizal (AM) fungi show high promiscuity in terms of host. Effector proteins expressed by AM fungi are found important in establishing interaction with host. However, the mechanistic underlying host-specific interactions of the fungi remain unknown. The present study aimed (i) to identify effectors encoded by Rhizophagus proliferus and (ii) to understand molecular specificity encoded in effectors for interaction with specific plant species. The effectors predicted from the whole genome sequence were annotated by homology search in NCBI non-redundant protein, Interproscan, and pathogen-host interaction (PHI) databases. In total, 416 small secreted peptides (SSPs) were predicted, which were effector peptides with presence of nuclear localization signal, small cysteine-rich, and repeat-containing proteins domains. Similar to the functionally validated SP7 effectors in Rhizophagus irregularis, two proteins (RP8598 and RP23081) were identified in R. proliferus. To understand whether interaction between SP7 and the plant target protein, ERF19, is specific in nature, we examined protein-peptide interaction using in silico molecular docking. Pairwise interaction of RP8598 and RP23081 with the ethylene-responsive factors (ERF19) coded by five different plant species (Lotus japonicus, Solanum lycopersicum, Ocimum tenuiflorum, Medicago truncatula, Diospyros kaki) was investigated. Prediction of high-quality interaction of SP7 effector with ERF19 protein expressed only by specific plant species was observed in in silico molecular docking, which may reiterate the role of effectors in host specificity. The outcomes from our study indicated that sequence precision encoded in the effector peptides of AM fungi and immunomodulatory proteins of host may regulate host specificity in these fungi.

The structure-function analysis of the Mpr1 metalloprotease determinants of activity during migration of fungal cells across the blood-brain barrier

Cryptococcal meningoencephalitis, the most common form of cryptococcosis, is caused by the opportunistic fungal pathogen, Cryptococcus neoformans. Molecular strategies used by C. neoformans to invade the central nervous system (CNS) have been the focus of several studies. Recently, the role of a novel secreted metalloprotease (Mpr1) in the pathogenicity of C. neoformans was confirmed by studies demonstrating that Mpr1 mediated the migration of fungal cells into the CNS. Given this central function, the aim here was to identify the molecular determinants of Mpr1 activity and resolve their role in the migration of cryptococci across the blood-brain barrier (BBB). The Mpr1 protein belongs to an understudied group of metalloproteases of the M36 class of fungalysins unique to fungi. They are generally synthesized as propeptides with fairly long prodomains and highly conserved regions within their catalytic core. Through structure-function analysis of Mpr1, our study identified the prodomain cleavage sites of Mpr1 and demonstrated that when mutated, the prodomain appears to remain attached to the catalytic C-terminus of Mpr1 rendering a nonfunctional Mpr1 protein and an inability for cryptococci to cross the BBB. We found that proteolytic activity of Mpr1 was dependent on the coordination of zinc with two histidine residues in the active site of Mpr1, since amino acid substitutions in the HExxH motif abolished Mpr1 proteolytic activity and prevented the migration of cryptococci across the BBB. A phylogenetic analysis of Mpr1 revealed a distinct pattern likely reflecting the neurotropic nature of C. neoformans and the specific function of Mpr1 in breaching the BBB. This study contributes to a deeper understanding of the molecular regulation of Mpr1 activity and may lead to the development of specific inhibitors that could be used to restrict fungal penetration of the CNS and thus prevent cryptococcal meningoencephalitis-related deaths.

Different patterns of extracellular proteolytic activity in W303a and BY4742 Saccharomyces cerevisiae strains

Protease secretion in Saccharomyces cerevisiae cultures is a complex process, important for the application of this organism in the food industry and biotechnology. Previous studies provide rather quantitative data, yielding no information about the number of enzymes involved in proteolysis and their individual biochemical properties. Here we demonstrate that W303a and BY4742 S. cerevisiae strains reveal different patterns of spontaneous and gelatin-induced extracellular proteolytic activity. We applied the gelatin zymography assay to track changes of the proteolytic profile in time, finding the protease secretion dependent on the growth phase and the presence of the protein inducer. Detected enzymes were characterized regarding their substrate specificity, pH tolerance, and susceptibility to inhibitors. In case of the W303a strain, only one type of gelatin-degrading secretory protease (presumably metalloproteinase) was observed. However, the BY4742 strain secreted different proteases of the various catalytic types, depending on the substrate availability. Our study brings the evidence that S. cerevisiae strains secrete several kinds of proteases depending on the presence and type of the substrate. Protein induction may cause not only quantitative but also qualitative changes in the extracellular proteolytic patterns.

Propeptides as modulators of functional activity of proteases

Most proteases are synthesized in the cell as precursor-containing propeptides. These structural elements can determine the folding of the cognate protein, function as an inhibitor/activator peptide, mediate enzyme sorting, and mediate the protease interaction with other molecules and supramolecular structures. The data presented in this review demonstrate modulatory activity of propeptides irrespective of the specific mechanism of action. Changes in propeptide structure, sometimes minor, can crucially alter protein function in the living organism. Modulatory activity coupled with high variation allows us to consider propeptides as specific evolutionary modules that can transform biological properties of proteases without significant changes in the highly conserved catalytic domains. As the considered properties of propeptides are not unique to proteases, propeptide-mediated evolution seems to be a universal biological mechanism.

Fungal inhibitors of proteolytic enzymes: classification, properties, possible biological roles, and perspectives for practical use

Peptidase inhibitors are ubiquitous regulatory proteins controlling catalytic activity of proteolytic enzymes. Interest in these proteins increased substantially after it became clear that they can be used for therapy of various important diseases including cancer, malaria, and autoimmune and neurodegenerative diseases. In this review we summarize available data on peptidase inhibitors from fungi, emphasizing their properties, biological role, and possible practical applications of these proteins in the future. A number of fungal peptidase inhibitors with unique structure and specificity of action have no sequence homology with other classes of peptidase inhibitors, thus representing new and specific candidates for therapeutic use. The main classifications of inhibitors in current use are considered. Available data on structure, mechanisms and conditions of action, and diversity of functions of peptidase inhibitors of fungi are analyzed. It is mentioned that on one side the unique properties of some inhibitors can be used for selective inhibition of peptidases responsible for initiation and development of pathogenic processes. On the other side, general inhibitory activity of other inhibitors towards peptidases of various catalytic classes might be able to provide efficient defense of transgenic plants against insect pests by overcoming compensatory synthesis of new peptidases by these pests in response to introduction of a fungal inhibitor. Together, the data analyzed in this review reveal that fungal inhibitors extend the spectrum of known peptidase inhibitors potentially suitable for use in medicine and agriculture.

A functional and structural study of the major metalloprotease secreted by the pathogenic fungusAspergillus fumigatus

Fungalysins are secreted fungal peptidases with the ability to degrade the extracellular matrix proteins elastin and collagen and are thought to act as virulence factors in diseases caused by fungi. Fungalysins constitute a unique family among zinc-dependent peptidases that bears low sequence similarity to known bacterial peptidases of the thermolysin family. The crystal structure of the archetype of the fungalysin family,Aspergillus fumigatusmetalloprotease (AfuMep), has been obtained for the first time. The 1.8 Å resolution structure of AfuMep corresponds to that of an autoproteolyzed proenzyme with separate polypeptide chains corresponding to the N-terminal prodomain in a binary complex with the C-terminal zinc-bound catalytic domain. The prodomain consists of a tandem of cystatin-like folds whose C-terminal end is buried into the active-site cleft of the catalytic domain. The catalytic domain harbouring the key catalytic zinc ion and its ligands, two histidines and one glutamic acid, undergoes a conspicuous rearrangement of its N-terminal end during maturation. One key positively charged amino-acid residue and the C-terminal disulfide bridge appear to contribute to its structural–functional properties. Thus, structural, biophysical and biochemical analysis were combined to provide a deeper comprehension of the underlying properties ofA. fumigatusfungalysin, serving as a framework for the as yet poorly known metallopeptidases from pathogenic fungi.

Identification of a chitinase-modifying protein from Fusarium verticillioides: truncation of a host resistance protein by a fungalysin metalloprotease

Chitinase-modifying proteins (cmps) are proteases secreted by fungal pathogens that truncate the plant class IV chitinases ChitA and ChitB during maize ear rot. cmp activity has been characterized for Bipolaris zeicola and Stenocarpella maydis, but the identities of the proteases are not known. Here, we report that cmps are secreted by multiple species from the genus Fusarium, that cmp from Fusarium verticillioides (Fv-cmp) is a fungalysin metalloprotease, and that it cleaves within a sequence that is conserved in class IV chitinases. Protein extracts from Fusarium cultures were found to truncate ChitA and ChitB in vitro. Based on this activity, Fv-cmp was purified from F. verticillioides. N-terminal sequencing of truncated ChitA and MALDI-TOF-MS analysis of reaction products showed that Fv-cmp is an endoprotease that cleaves a peptide bond on the C-terminal side of the lectin domain. The N-terminal sequence of purified Fv-cmp was determined and compared with a set of predicted proteins, resulting in its identification as a zinc metalloprotease of the fungalysin family. Recombinant Fv-cmp also truncated ChitA, confirming its identity, but had reduced activity, suggesting that the recombinant protease did not mature efficiently from its propeptide-containing precursor. This is the first report of a fungalysin that targets a nonstructural host protein and the first to implicate this class of virulence-related proteases in plant disease.

Fungal proteases and their pathophysiological effects

Proteolytic enzymes play an important role in fungal physiology and development. External digestion of protein substrates by secreted proteases is required for survival and growth of both saprophytic and pathogenic species. Extracellular serine, aspartic, and metalloproteases are considered virulence factors of many pathogenic species. New findings focus on novel membrane-associated proteases such as yapsins and ADAMs and their role in pathology. Proteases from fungi induce inflammatory responses by altering the permeability of epithelial barrier and by induction of proinflammatory cytokines through protease-activated receptors. Many fungal allergens possess proteolytic activity that appears to be essential in eliciting Th2 responses. Allergenic fungal proteases can act as adjuvants, potentiating responses to other allergens. Proteolytic enzymes from fungi contribute to inflammation through interactions with the kinin system as well as the coagulation and fibrinolytic cascades. Their effect on the host protease-antiprotease balance results from activation of endogenous proteases and degradation of protease inhibitors. Recent studies of the role of fungi in human health point to the growing importance of proteases not only as pathogenic agents in fungal infections but also in asthma, allergy, and damp building related illnesses. Proteolytic enzymes from fungi are widely used in biotechnology, mainly in food, leather, and detergent industries, in ecological bioremediation processes and to produce therapeutic peptides. The involvement of fungal proteases in diverse pathological mechanisms makes them potential targets of therapeutic intervention and candidates for biomarkers of disease and exposure.

An expanded family of fungalysin extracellular metallopeptidases of Coprinopsis cinerea

Proteolytic enzymes, particularly secreted proteases of fungal origin, are among the most important of industrial enzymes, yet the biochemical properties and substrate specificities of these proteins have been difficult to characterize. Genomic sequencing offers a powerful tool to identify potentially novel proteases. The genome of the model basidiomycete Coprinopsis cinereus was found to have an unusually high number of metalloproteases that closely match the M36 peptidase family known as fungalysins. The eight predicted C. cinereus fungalysins divide into two groups upon comparison with fungalysins from other fungi. One member, CcMEP1, is most similar to the single representative fungalysins from the basidiomycetes Phanerochaete chrysosporium, Cryptococcus neoformans, and Ustilago maydis, and to the fungalysin type-protein from Aspergillus fumigatus. The remaining seven C. cinereus predicted fungalysins form a group with similarity to three predicted M36 peptidases of Laccaria bicolor. All eight of the C. cinereus enzymes contain both the signature M36 Pfam domain and the FTP propeptide domain. All contain large propeptides with considerable sequence conservation near a proposed cleavage site. The predicted mature enzymes range in size from 37-46 kDa and have isoelectric points that are mildly acidic to neutral. The proximity of these genes to telomeres and/or to transposable elements may have contributed to the expansion of this gene family in C. cinereus.

The N-terminal propeptide of Vibrio vulnificus extracellular metalloprotease is both an inhibitor of and a substrate for the enzyme

Vibrio vulnificus, a marine bacterium capable of causing wound infection and septicemia, secretes a 45-kDa metalloprotease (vEP) with many biological activities. The precursor of vEP consists of four regions: a signal peptide, an N-terminal propeptide (nPP), a C-terminal propeptide, and the mature protease. Two forms of vEP-vEP-45, which contains the mature protease plus the C-terminal propeptide, and vEP-34, which contains only the mature protease-were expressed in Escherichia coli and purified. vEP-45 and vEP-34 had similar activities with azocasein as a substrate, but vEP-34 had reduced activity toward insoluble proteins. The nPP of vEP was expressed as a His tag fusion protein, and its effect on vEP activity was investigated. nPP inhibited the activities of both vEP-45 and vEP-34 but not that of thermolysin, a different but related zinc-dependent protease. The inhibition of vEP by nPP was further examined using vEP-34 as a representative enzyme. The inhibition could be completely reversed under conditions of low enzyme and propeptide concentrations and with prolonged incubation, which resulted from the degradation of nPP by vEP. However, even at high nPP and vEP concentrations, inhibition of vEP by nPP at high temperatures was not effective, resulting in the degradation of both nPP and vEP. These results demonstrate that the nPP of vEP could bind to vEP and inhibit its activity, resulting in the degradation of the propeptide.

Activity-based identification of secreted serine proteases of the filamentous fungus, Ophiostoma

A general activity probe was synthesized and applied to the supernatant of a filamentous fungus, Ophiostoma, culture to identify directly the secreted serine proteases by covalent enzyme labeling. The activity probe contained a chemically reactive group that reacted with, and thus covalently labeled, the serine residues of only active proteases and not heat-inactivated proteases. The activity probe also contained a fluorescent group that allowed for the subsequent visualization of the captured proteases in 1-D gels and their identification by N-terminal sequencing. This use of a chemical probe led to the rapid discovery of subtilisin-like serine protease of Ophiostoma. Two hypothetical proteins were also captured, with one being a probable endopeptidase K type of protease.

Tvbgn3, a beta-1,6-glucanase from the biocontrol fungus Trichoderma virens, is involved in mycoparasitism and control of Pythium ultimum

Even though beta-1,6-glucanases have been purified from several filamentous fungi, the physiological function has not been conclusively established for any species. In the present study, the role of Tvbgn3, a beta-1,6-glucanase from Trichoderma virens, was examined by comparison of wild-type (WT) and transformant strains in which Tvbgn3 was disrupted (GKO) or constitutively overexpressed (GOE). Gene expression analysis revealed induction of Tvbgn3 in the presence of host fungal cell walls, indicating regulation during mycoparasitism. Indeed, while deletion or overexpression of Tvbgn3 had no evident effect on growth and development, GOE and GKO strains showed an enhanced or reduced ability, respectively, to inhibit the growth of the plant pathogen Pythium ultimum compared to results with the WT. The relevance of this activity in the biocontrol ability of T. virens was confirmed in plant bioassays. Deletion of the gene resulted in levels of disease protection that were significantly reduced from WT levels, while GOE strains showed a significantly increased biocontrol capability. These results demonstrate the involvement of beta-1,6-glucanase in mycoparasitism and its relevance in the biocontrol activity of T. virens, opening a new avenue for biotechnological applications.

Direct activation of gelatinase B (MMP-9) by hay dust suspension and different components of organic dust

Matrix metalloproteinases (MMPs) are involved in tissue destruction in allergic airway diseases. We studied the ability of various allergenic substances to directly activate recombinant 92kDa proMMP-9. The substances included hay dust suspension (HDS) and its components (supernatant, particulate matter and wash fluid of particulate matter), storage mite extract and two Aspergillus fumigatus extracts. The allergen suspensions were incubated in vitro with proMMP-9. After incubation the conversion of proMMP-9 to 10kDa lower active forms were studied using gelatin zymography and Western immunoblot quantified by computerized densitometry. All studied allergens except HDS significantly and efficiently activated proMMP-9 as compared to a negative control. At the concentrations employed, the most potent activators were A. fumigatus extracts and mite suspension. The greater potency of mite and fungi as proMMP-9 activators suggests that these allergens may be more damaging to airways even at low concentrations.

Function of the signal peptide and N- and C-terminal propeptides in the leucine aminopeptidase from Aeromonas proteolytica

The leucine aminopeptidase from Aeromonas proteolytica (also known as Vibrio proteolyticus) (AAP) is a metalloenzyme with broad substrate specificity. The open reading frame (ORF) for AAP encodes a 54 kDa enzyme, however, the extracellular enzyme has a molecular weight of 43 kDa. This form of AAP is further processed to a mature, thermostable 32 kDa form but the exact nature of this process is unknown. Over-expression of different forms of AAP in Escherichia coli (with AAP's native leader sequence, with and without the N- and/or C-terminal propeptides, and as fusion protein) has allowed a model for the processing of wild-type AAP to be proposed. The role of the A. proteolytica signal peptide in protein secretion as well as comparison to other known signal peptides reveals a close resemblance of the A. proteolytica signal peptide to the outer membrane protein (OmpA) signal peptide. Over-expression of the full 54 kDa AAP enzyme provides an enzyme that is significantly less active, due to a cooperative inhibitory interaction between both propeptides. Over-expression of AAP lacking its C-terminal propeptide provided an enzyme with an identical kcat value to wild-type AAP but exhibited a larger Km value, suggesting competitive inhibition of AAP by the N-terminal propeptide (Ki approximately 0.13 nM). The recombinant 32 kDa form of AAP was characterized by kinetic and spectroscopic methods and was shown to be identical to mature, wild-type AAP. Therefore, the ease of purification and processing of rAAP along with the fact that large quantities can be obtained now allow new detailed mechanistic studies to be performed on AAP through site-directed mutagenesis.

Functional analysis of tvsp1, a serine protease-encoding gene in the biocontrol agent Trichoderma virens

Serine proteases are highly conserved among fungi and considered to play a key role in different aspects of fungal biology. These proteases can be involved in development and have been related to pathogenesis or biocontrol processes. A gene (tvsp1) encoding an extracellular serine protease was cloned from Trichoderma virens, a biocontrol agent effective against soilborne fungal pathogens. The gene was expressed in Escherichia coli and a polyclonal antibody was raised against the recombinant protein. The expression pattern of tvsp1 was determined and its physiological role was addressed by mutational analysis. Strains of T. virens in which tvsp1 was deleted (PKO) or constitutively overexpressed (POE) were not affected in growth rate, conidiation, extracellular protein accumulation, antibiotic profiles nor in their ability to induce phytoalexins in cotton seedlings. Tvsp1 overexpression, however, significantly increased the ability of some strains to protect cotton seedlings against Rhizoctonia solani. Our data show that Tvsp1 is not necessary for the normal growth or development of T. virens, but plays a role in the biocontrol process.

The role of the Aspergillus niger furin-type protease gene in processing of fungal proproteins and fusion proteins

We have characterized growth and protein processing characteristics of Aspergillus niger strains carrying a disrupted allele of the previously cloned and characterized kexB gene [Appl. Environ. Microbiol. 66 (2000) 363] encoding a furin-type endoprotease. Deletion of the single-copy gene confirms it to be non-essential but disruptant strains exhibit a morphologically distinct phenotype characterized by hyperbranching. Processing of homologous pro-proteins and fusion proteins comprised of a heterologous protein fused down-stream of glucoamylase and separated at the fusion junction by an endoproteolytic cleavage site was compared in wildtype and mutant strains of A. niger. We show that maturation of the native glucoamylase requires KexB, whereas maturation of aspergillopepsin does not. The processing of fusion proteins carrying Lys-Arg requires KexB, although alternative endoproteases are capable of cleaving protein fusions at sites adjacent to Lys-Arg.

Functional characterization of the propeptide of Plasmodium falciparum subtilisin-like protease-1

Erythrocyte invasion by the malaria merozoite is prevented by serine protease inhibitors. Various aspects of the biology of Plasmodium falciparum subtilisin-like protease-1 (PfSUB-1), including the timing of its expression and its apical location in the merozoite, suggest that this enzyme is involved in invasion. Recombinant PfSUB-1 expressed in a baculovirus system is secreted in the p54 form, noncovalently bound to its cognate propeptide, p31. To understand the role of p31 in PfSUB-1 maturation, we examined interactions between p31 and both recombinant and native enzymes. CD analyses revealed that recombinant p31 (rp31) possesses significant secondary structure on its own, comparable with that of folded propeptides of some bacterial subtilisins. Kinetic studies demonstrated that rp31 is a fast binding, high affinity inhibitor of PfSUB-1. Inhibition of two bacterial subtilisins by rp31 was much less effective, with inhibition constants 49-60-fold higher than that for PfSUB-1. Single (at the P4 or P1 position) or double (at P4 and P1 positions) point mutations of residues within the C-terminal region of rp31 had little effect on its inhibitory activity, and truncation of 11 residues from the rp31 C terminus substantially reduced, but did not abolish, inhibition. None of these modifications prevented binding to the PfSUB-1 catalytic domain or rendered the propeptide susceptible to proteolytic digestion by PfSUB-1. These studies provide new insights into the function of the propeptide in PfSUB-1 activation and shed light on the structural requirements for interaction with the catalytic domain.

Maturation of barley cysteine endopeptidase expressed in Trichoderma reesei is distorted by incomplete processing

Maturation of barley cysteine endopeptidase B (EPB) in Trichoderma reesei was studied with metabolic in hibitors, Western blotting, and immuno microscopy. The inactive 42-kDa recombinant EPB proprotein, first detected in apical cells, was sequentially processed in a time-dependent manner to a secreted polypeptide of 38.5 kDa, and thereafter, to polypeptides of 37.5, 35.5, and 32 kDa exhibiting enzyme activity both in the hyphae and culture medium. The sizes of the different forms of recombinant EPB were in accordance with molecular masses calculated from the deduced amino acid sequence, assuming cleavage at four putative Kex2p sites present in the 42-kDa proprotein. Both the liquid and the zymogram in-gel activity assays indicated that the 32-kDa enzyme produced in T. reesei in vivo was 2 kDa larger and four times less active than the endogenous EPB. Brefeldin A treatment prevented the last Kex2p processing step of EPB from a 35.5- to a 32-kDa protein. This coincided with a significant increase in the immuno-gold label for EPB and in modified Golgi-like bodies, which suggests that the processing step probably took place in medial Golgi. A 30.5-kDa EPB polypeptide was observed when glycosylation was inhibited by tunicamycin (TM) or when deglycosylation was carried out enzymatically. Deglycosylation increased the enzyme activity twofold, which was also indicated by an increased fluorescence by TM treatment in the zymogram in-gel activity assay. Simultaneous incubation with TM and monensin produced a peptide of 31.5 kDa. Therefore, monensin may inhibit the final processing step of an unglycosylated EPB by an unknown protease in the fungus. In any case, the final recombinant EPB product in Trichoderma differs from the mature endogenous 30-kDa enzyme produced in barley.

Propeptide of the metalloprotease of Brevibacillus brevis 7882 is a strong inhibitor of the mature enzyme

A metalloprotease gene of Brevibacillus brevis (npr) was expressed in Escherichia coli in a soluble form as native Npr precursor. A significant fraction of the precursor was spontaneously processed, producing the N-terminal propeptide and the mature enzyme. A strong inhibition of the mature Npr by its own propeptide in the crude lysate was observed even in the absence of the covalent linkage between them. Pure precursor, propeptide and the mature Npr were isolated and kinetic parameters of the mature enzyme inhibition by the propeptide were determined. The inhibition is of the tight-binding competitive type with Ki 0.17 nM. Inhibition of metalloproteases from Brevibacillus megaterium and thermolysine by the heterologous propeptide of the Npr from B. brevis was much weaker or none.

The inhibitory properties and primary structure of a novel serine proteinase inhibitor from the fruiting body of the basidiomycete, Lentinus edodes

A novel proteinase inhibitor, Lentinus proteinase inhibitor, has been purified from the fruiting bodies of the edible mushroom, Lentinus edodes, by buffer extraction and affinity chromatography on immobilized anhydrotrypsin. The protein simultaneously inhibits bovine beta-trypsin and alpha-chymotrypsin at independent sites, with apparent dissociation constants of 3.5 x 10(-10) M and 4 x 10(-8) M, respectively. The purified protein is eluted as two well-separated peaks on reversed-phase HPLC, one of which is inhibitory-active and the other inactive, and they are interconvertible under folding/unfolding conditions. Among the mammalian and microbial serine proteinases examined, including human enzymes of blood coagulation and fibrinolysis, activated factor XI was inhibited by the Lentinus proteinase inhibitor. Chemical modification studies suggest involvement of one or more arginine residues in the inhibition of trypsin. The complete primary structure composed of 142 amino acids with an acetylated N-terminus was determined by protein analysis. The theoretical molecular mass (15999.2) from the sequence is close to the experimental value of 15999.61 +/- 0.61 determined by mass spectrometry. Although there are no apparently homologous proteinase inhibitors in the protein database, there is a rather striking similarity to the propeptide segment of a microbial serine proteinase, as well as to the N-terminal region of the mature enzyme.

Aspergillus fumigatus and aspergillosis

Aspergillus fumigatus is one of the most ubiquitous of the airborne saprophytic fungi. Humans and animals constantly inhale numerous conidia of this fungus. The conidia are normally eliminated in the immunocompetent host by innate immune mechanisms, and aspergilloma and allergic bronchopulmonary aspergillosis, uncommon clinical syndromes, are the only infections observed in such hosts. Thus, A. fumigatus was considered for years to be a weak pathogen. With increases in the number of immunosuppressed patients, however, there has been a dramatic increase in severe and usually fatal invasive aspergillosis, now the most common mold infection worldwide. In this review, the focus is on the biology of A. fumigatus and the diseases it causes. Included are discussions of (i) genomic and molecular characterization of the organism, (ii) clinical and laboratory methods available for the diagnosis of aspergillosis in immunocompetent and immunocompromised hosts, (iii) identification of host and fungal factors that play a role in the establishment of the fungus in vivo, and (iv) problems associated with antifungal therapy.

The inhibition of cathepsin S by its propeptide--specificity and mechanism of action

The interaction of human recombinant full-length cathepsin S propeptide (amino acids 16-114) with mature cysteine proteinases was studied with respect to selectivity and pH dependence. The inhibitory capacity was tested towards mature human recombinant cathepsin S, purified cathepsin L from rat and Paramecium tetraurelia, rat cathepsin B, human cathepsin H, and papain. The propeptide of cathepsin S strongly inhibited cathepsin S (Ki = 0.27 nM) and the two cathepsin L species (Ki = 0.36 nM) at neutral pH. Papain, and to a minor extent cathepsin H, hydrolyzed the propeptide of cathepsin S, leading to competition with the hydrolysis of the fluorogenic substrates in the respective assays. Cathepsin B activity was nearly unaffected up to micromolar propeptide concentrations in the assay. The inhibition of cathepsin-L-like peptidases was diminished with decreasing pH, probably due to dramatic changes in the conformation of the propeptide. This assumption was supported by far-ultraviolet CD spectroscopy and by the finding of rapid hydrolysis of the cathepsin S propeptide by cathepsin L at pH values less than 5.5.

Most of the propeptide is dispensable for stability and autoprocessing of the zymogen of the germination protease of spores of Bacillus species

Loss of 3, 7, or 10 of the amino-terminal 15 residues removed upon autoactivation of the zymogen of the germination protease (GPR), which initiates protein degradation during germination of spores of Bacillus species, did not result in significant changes in (i) the lack of enzymatic activity of the zymogen, (ii) the rate of zymogen autoactivation, or (iii) the unreactivity of the zymogen's single SH group. Removal of 13 amino-terminal residues resulted in a partially active enzyme whose SH group was as reactive as the fully active enzyme. These findings suggest that at least a part of the propeptide blocks access to the enzyme's active site. However, the free propeptide did not inhibit the enzyme.