Oligopeptidase B from L. amazonensis: molecular cloning, gene expression analysis and molecular model

Molecular dynamics complemented by site-directed mutagenesis reveals significant difference between the interdomain salt bridge networks stabilizing oligopeptidases B from bacteria and protozoa in their active conformations

Oligopeptidases B (OpdBs) are trypsin-like peptidases from protozoa and bacteria that belong to the prolyl oligopeptidase (POP) family. All POPs consist of C-terminal catalytic domain and N-terminal β-propeller domain and exist in two major conformations: closed (active), where the domains and residues of the catalytic triad are positioned close to each other, and open (non-active), where two domains and residues of the catalytic triad are separated. The interdomain interface, particularly, one of its salt bridges (SB1), plays a role in the transition between these two conformations. However, due to double amino acid substitution (E/R and R/Q), this functionally important SB1 is absent in γ-proteobacterial OpdBs including peptidase from Serratia proteamaculans (PSP). In this study, molecular dynamics was used to analyze inter- and intradomain interactions stabilizing PSP in the closed conformation, in which catalytic H652 is located close to other residues of the catalytic triad. The 3D models of either wild-type PSP or of mutant PSPs carrying activating mutations E125A and D649A in complexes with peptide-substrates were subjected to the analysis. The mechanism that regulates transition of H652 from active to non-active conformation upon domain separation in PSP and other γ-proteobacterial OpdB was proposed. The complex network of polar interactions within H652-loop/C-terminal α-helix and between these areas and β-propeller domain, established in silico, was in a good agreement with both previously published results on the effects of single-residue mutations and new data on the effects of the activating mutations on each other and on the low active mutant PSP-K655A.Communicated by Ramaswamy H. Sarma.

Leishmanicidal therapy targeted to parasite proteases

Leishmaniasis is considered a serious public health problem and the current available therapy has several disadvantages, which makes the search for new therapeutic targets and alternative treatments extremely necessary. In this context, this review focuses on the importance of parasite proteases as target drugs against Leishmania parasites, as a chemotherapy approach. Initially, we discuss about the current scenario for the treatment of leishmaniasis, highlighting the main drugs used and the problems related to their use. Subsequently, we describe the inhibitors of major proteases of Leishmania already discovered, such as Compound s9 (aziridine-2,3-dicarboxylate), Compound 1c (benzophenone derivative), Au2Phen (gold complex), AubipyC (gold complex), MDL 28170 (dipeptidyl aldehyde), K11777, Hirudin, diazo-acetyl norleucine methyl ester, Nelfinavir, Saquinavir, Nelfinavir, Saquinavir, Indinavir, Saquinavir, GNF5343 (azabenzoxazole), GNF6702 (azabenzoxazole), Benzamidine and TPCK. Next, we discuss the importance of the protease gene to parasite survival and the aspects of the validation of proteases as target drugs, with emphasis on gene disruption. Then, we describe novel important strategies that can be used to support the research of new antiparasitic drugs, such as molecular modeling and nanotechnology, whose main targets are parasitic proteases. And finally, we discuss possible perspectives to improve drug development. Based on all findings, proteases could be considered potential targets against leishmaniasis.

Oligopeptidase B and B2: comparative modelling and virtual screening as searching tools for new antileishmanial compounds

Leishmaniasis are diseases caused by parasites of the genus Leishmania and transmitted to humans by the bite of infected insects of the subfamily Phlebotominae. Current drug therapy shows high toxicity and severe adverse effects. Recently, two oligopeptidases (OPBs) were identified in Leishmania amazonensis, namely oligopeptidase B (OPB) and oligopeptidase B2 (OPB2). These OPBs could be ideal targets, since both enzymes are expressed in all parasite lifecycle and were not identified in human. This work aimed to identify possible dual inhibitors of OPB and OPB2 from L. amazonensis. The three-dimensional structures of both enzymes were built by comparative modelling and used to perform a virtual screening of ZINC database by DOCK Blaster server. It is the first time that OPB models from L. amazonensis are used to virtual screening approach. Four hundred compounds were identified as possible inhibitors to each enzyme. The top scored compounds were submitted to refinement by AutoDock program. The best results suggest that compounds interact with important residues, as Tyr490, Glu612 and Arg655 (OPB numbers). The identified compounds showed better results than antipain and drugs currently used against leishmaniasis when ADMET in silico were performed. These compounds could be explored in order to find dual inhibitors of OPB and OPB2 from L. amazonensis.

Truncated Variants of Serratia proteamaculans Oligopeptidase B Having Different Activities

Treatment of native psychrophilic oligopeptidase B from Serratia proteamaculans (PSP, 78 kDa) with chymotrypsin (soluble or immobilized on modified porous glass MPG-PA) in the presence of 50% glycerol leads to production of a truncated enzyme form (PSP-Chtr, ~66 kDa), which retains activity toward the low molecular weight substrate of PSP, BAPNA, but in contrast to PSP, is active toward the protein substrate azocasein. It has been shown by MALDI-TOF mass-spectrometry that PSP-Chtr lacks the N-terminal region of the molecule that envelops the catalytic domain of PSP and supposedly prevents hydrolysis of high molecular weight substrates. It has also been established that the lacking fragment corresponds to the N-terminal highest rank element of the informational structure of PSP. This finding confirms the usefulness of the method of informational structure analysis for protein engineering of enzymes. A similar treatment of PSP with immobilized trypsin also led to production of a stable truncated enzyme form (PSP-Tr, ~75 kDa) which lacked 22 C-terminal amino acid residues and completely lost enzymatic activity, presumably because of changes in the nearest environment of His652 of the catalytic triad.

The oligopeptidase B of Leishmania regulates parasite enolase and immune evasion

Proteases are a ubiquitous group of enzymes that play key roles in the life cycle of parasites, in the host-parasite relationship, and in the pathogenesis of parasitic diseases. Furthermore, proteases are targets for the development of new anti-parasitic therapy. Protozoan parasites like Leishmania predominantly express Clan CA cysteine proteases for key life cycle functions. It was therefore unexpected to find a high level of serine protease activity expressed by Leishmania donovani. Purification of this activity followed by mass spectrometry identified oligopeptidase B (OPB; Clan SC, family S9A) as the responsible enzyme. This was confirmed by gene knock-out of OPB, which resulted in the disappearance of the detected serine protease activity of Leishmania extracts. To delineate the specific role of OPB in parasite physiology, proteomic analysis was carried out on OPB(-/-) versus wild type parasites. Four protein species were significantly elevated in OPB(-/-) parasites, and all four were identified by mass spectrometry as enolase. This increased enolase was enzymatically inactive and associated with the parasite membrane. Aside from its classic role in carbohydrate metabolism, enolase was recently found to localize to membranes, where it binds host plasminogen and functions as a virulence factor for several pathogens. As expected, there was a striking alteration in macrophage responses to Leishmania when OPB was deleted. Whereas wild type parasites elicited little, if any, response from infected macrophages, OPB(-/-) parasites induced a massive up-regulation in gene transcription. Additionally, these OPB(-/-) parasites displayed decreased virulence in the murine footpad infection model.

Oligopeptidase B deficient mutants of Leishmania major

Oligopeptidase B is a clan SC, family S9 serine peptidase found in gram positive bacteria, plants and trypanosomatids. Evidence suggests it is a virulence factor and thus therapeutic target in both Trypanosoma cruzi and T. brucei, but little is known about its function in Leishmania. In this study L. major OPB-deficient mutants (Δopb) were created. These grew normally as promastigotes, had a small deficiency in their ability to undergo differentiation to metacyclic promastigotes, were significantly less able to infect and survive within macrophages in vitro, but were virulent to mice. These data suggest that L. major OPB itself is not an important virulence factor, indicating functional differences between trypanosomes and Leishmania in their interaction with the mammalian host. The possibility that an OPB-like enzyme (designated OPB2) in L. major might compensate for the loss of OPB in Δopb was investigated via by mapping its sequence onto the 1.6Å structure of L. major OPB. This suggested that the residues involved in the S1 and S2 subsites of OPB2 are identical to OPB and hence the substrate specificity would be similar. Consequently there may be redundancy between the two enzymes.

A critical role for highly conserved Glu(610) residue of oligopeptidase B from Trypanosoma brucei in thermal stability

Oligopeptidase B from Trypanosoma brucei (Tb OPB) is a virulence factor and therapeutic target in African sleeping sickness. Three glutamic acid residues at positions 607, 609 and 610 of the catalytic domain are highly conserved in the OPB subfamily. In this study, the roles of Glu(607), Glu(609) and Glu(610) in Tb OPB were investigated by site-directed mutagenesis. A striking effect on k(cat)/K(m) was obtained following mutation of Glu(607) to glutamine. In contrast, the heat stability of Tb OPB decreased markedly following the single mutation of Glu(610) to glutamine, although this mutation had significantly less effect on catalytic properties compared with the Glu(607) mutation. Although no differences were found in the tertiary and secondary structures between wild-type (WT) OPB and the E610Q mutant prior to heat treatment, the E610Q mutant is inactivated more rapidly than WT OPB following heat treatment in a manner correlating with its attendant structural changes. Trypsin digestion showed that the boundary regions between the beta-propeller and catalytic domain of the E610Q mutant are unfolded with heat treatment. It is concluded that Glu(607) is essential for the catalytic activity of Tb OPB and that Glu(610) plays a critical role in stabilization rather than catalytic activity despite their close proximity.

Development of protease inhibitors for protozoan infections

PURPOSE OF REVIEW

To highlight the promise of parasite proteases as targets for development of new antiparasitic chemotherapy. Proteolytic enzymes play key roles in the life cycle of protozoan parasites or the pathogenesis of diseases they produce. These roles include processing of host or parasite surface proteins for invasion of host cells, digestion of host proteins for nutrition, and inactivation of host immune defense mediators.

RECENT FINDINGS

Drug development for other markets has shown that proteases are druggable targets, and protease inhibitors are now licensed or in clinical development to treat hypertension, diabetes, thrombosis, osteoporosis, infectious diseases, and cancer. Several protease targets have been validated by genetic or chemical knockout in protozoan parasites. Many other parasite proteases appear promising as targets, but require more work for validation, or to identify viable drug leads. Because homologous proteases function as key enzymes in several parasites, targeting these proteases may allow development of a single compound, or a set of similar compounds, that target multiple diseases including malaria, trypanosomiasis, leishmaniasis, toxoplasmosis, cryptosporidiosis, and amebiasis.

SUMMARY

Proteases have been validated as targets in a number of parasitic infections. Proteases are druggable targets as evidenced by effective antiprotease drugs for the treatment of many human diseases including hypertension and AIDS. Future drug development targeting parasite proteases will be aided by the strong foundation of biochemical, structural, and computational databases already published or available online.

Modulation of dendritic cell function by Leishmania parasites

The interactions between Leishmania parasites and dendritic cells (DCs) are complex and involve paradoxical functions that can stimulate or halt T cell responses, leading to the control of infection or progression of disease. The magnitude and profile of DC activation vary greatly, depending upon the Leishmania species/strains, developmental stages, DC subsets, serum opsonization, and exogenous DC stimuli involved in the study. In general, the uptake of Leishmania parasites alone can trigger relatively weak and transient DC activation; however, the intracellular parasites (amastigotes) are capable of down-modulating LPS/IFN-gamma-stimulated DC activation via multiple mechanisms. This review will highlight current data regarding the initial interaction of DC subsets with invading parasites, the alterations of DC signaling pathways and function by amastigotes, and the impact of DC functions on protective immunity and disease pathogenesis. Available information provides insight into the mechanisms by which DCs discriminate between the types of pathogens and regulate appropriate immune responses.