Falcipain 2 and 3 as malarial drug targets: deciphering the effects of missense mutations and identification of allosteric modulators via computational approaches
- Authors: Okeke, Chiamaka Jessica
- Date: 2023-10-13
- Subjects: Antimalarials , Cysteine proteinases , Missense mutation , Allostery , Cysteine proteinase falcipain 2a , Cysteine proteinase falcipain 3
- Language: English
- Type: Academic theses , Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/432170 , vital:72848 , DOI 10.21504/10962/432170
- Description: Malaria, caused by an obligate unicellular protozoan parasite of the genus Plasmodium, is a disease of global health importance that remains a major cause of morbidity and mortality in developing countries. The World Health Organization (WHO) reported nearly 247 million malaria cases in 2021, causing 619,000 deaths, the vast majority ascribed to pregnant women and young children in sub-Saharan Africa. A critical component of malaria mitigation and elimination efforts worldwide is antimalarial drugs. However, resistance to available antimalarial drugs jeopardizes the treatment, prevention, and eradication of the disease. The recent emergence and spread of resistance to artemisinin (ART), the currently recommended first-line antimalarial drug, emphasizes the need to understand the resistance mechanism and apply this knowledge in developing new drugs that are effective against malaria. An insight into ART's mechanism of action indicates that ferrous iron (Fe2+) or heme, released when hemoglobin is degraded, cleaves the endoperoxide bridge. As a result, free radicals are formed, which alkylate many intracellular targets and result in plasmodial proteopathy. Aside from the existing evidence that mutations in the Kelch 13 protein propeller domain affect ART sensitivity and clearance rate by Plasmodium falciparum (Pf) parasites, recent investigations raise the possibility that additional target loci may be involved, and these include a nonsense (S69stop) and four missense variants (K255R, N257E, T343P, and D345G) in falcipain 2 (FP-2) protein. FP-2 and falcipain 3 (FP-3) are cysteine proteases responsible for hydrolyzing hemoglobin in the host erythrocytic cycle, a key virulence factor for malaria parasite growth and metabolism. Due to the obligatory nature of the hemoglobin degradation process, both proteases have become potential antimalarial drug targets attracting attention in recent years for the development of blood-stage antimalarial drugs. The alteration of the expression profile of FP-2 and FP-3 through gene manipulation approaches (knockout) or compound inhibition assays, respectively, induced parasites with swollen food vacuoles due to the accumulation of undegraded hemoglobin. Furthermore, missense mutations in FP-2 confer parasites with decreased ART sensitivity, probably due to altered enzyme efficiency and momentary decreased hemoglobin degradation. Hence, understanding how these mutations affect FP-2 (including those implicated in ART resistance) and FP-3 is imperative to finding potentially effective inhibitors. The first aim of this thesis is to characterize the effects of missense mutations on the partial zymogen complex and the catalytic domain of FP-2 and FP-3 using a range of computational approaches and tools such as homology modeling, molecular dynamics (MD) simulations, comparative essential dynamics, dynamic residue network (DRN) analysis, weighted residue contact map analysis, amongst others. The Pf genomic resource database (PlasmoDB) identified 41 missense mutations located in the partial zymogen and catalytic domains of FP-2 and FP-3. Using structure-based tools, six putative allosteric pockets were identified in FP-2 and FP-3. The effect of mutations on the whole protein, the central core, binding pocket residues and allosteric pockets was evaluated. The accurate 3D homology models of the WT and mutants were calculated. MD simulations were performed on the various systems as a quick starting point. MD simulations have provided a cornerstone for establishing numerous computational tools for describing changes arising from mutations, ligand binding, and environmental changes such as pH and temperature. Post-MD analysis was performed in two stages viz global and local analysis. Global analysis via radius of gyration (Rg) and comparative essential dynamic analysis revealed the conformational variability associated with all mutations. In the catalytic domain of FP-2, the presence of M245I mutation triggered the formation of a cryptic pocket via an exclusive mechanism involving the fusion of pockets 2 and 6. This striking observation was also detected in the partial zymogen complex of FP-2 and induced by A159V, M245I and E249A mutations. A similar observation was uncovered in the presence of A422T mutation in the catalytic domain of FP-3. Local DRN and contact map analyses identified conserved inter-residue interaction changes on important communication networks. This study brings a novel understanding of the effects of missense mutations in FP-2 and FP-3 and provides important insight which may help discover new anti-hemoglobinase drugs. The second aim is the identification of potential allosteric ligands against the WT and mutant systems of FP-2 and FP-3 using various computational tools. Of the six potential allosteric pockets identified in FP-2 and FP-3, pocket 1 was evaluated by SiteMap as the most druggable in both proteins. This pipeline was implemented to screen pocket 1 of FP-2 and FP-3 against 2089 repositionable compounds obtained from the DrugBank database. In order to ensure selectivity and specificity to the Plasmodium protein, the human homologs (Cat K and Cat L) were screened, and compounds binding to these proteins were exempted from further analysis. Subsequently, eight compounds (DB00128, DB00312, DB00766, DB00951, DB02893, DB03754, DB13972, and DB14159) were identified as potential allosteric hits for FP-2 and five (DB00853, DB00951, DB01613, DB04173 and DB09419) for FP-3. These compounds were subjected to MD simulation and post-MD trajectory analysis to ascertain their stability in their respective protein structures. The effects of the stable compounds on the WT and mutant systems of FP-2 and FP-3 were then evaluated using DRN analysis. Attention has recently been drawn towards identifying novel allosteric compounds targeting FP-2 and FP-3; hence this study explores the potential allosteric inhibitory mechanisms in the presence and absence of mutations in FP-2 and FP-3. Overall, the results presented in this thesis provide (i) an understanding of the role mutations in the partial zymogen complex play in the activation of the active enzyme, (ii) an insight into the possible allosteric mechanisms induced by mutations on the active enzymes, and (iii) a computational pipeline for the development of novel allosteric modulators for malaria inhibition studies. , Thesis (PhD) -- Faculty of Science, Biochemistry and Microbiology, 2023
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- Date Issued: 2023-10-13
Comparative study of clan CA cysteine proteases: an insight into the protozoan parasites
- Authors: Moyo, Sipho Dugunye
- Date: 2015
- Subjects: Cysteine proteinases , Proteolytic enzymes , Protozoan diseases , Parasites , Protozoan diseases -- Chemotherapy , Bioinformatics , Plasmodium , Antiprotozoal agents
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4165 , http://hdl.handle.net/10962/d1020309
- Description: Protozoan infections such as Malaria, Leishmaniasis, Toxoplasmosis, Chaga’s disease and African trypanosomiasis caused by the Plasmodium, Leishmania, Toxoplasma and Trypanosoma genuses respectively; inflict a huge economic, health and social impact in endemic regions particularly tropical and sub-tropical regions. The combined infections are estimated at over a billion annually and approximately 1.1 million deaths annually. The global burden of the protozoan infections is worsened by the increased drug resistance, toxicity and the relatively high cost of treatment and prophylaxis. Therefore there has been a high demand for new drugs and drug targets that play a role in parasite virulence. Cysteine proteases have been validated as viable drug targets due to their role in the infectivity stage of the parasites within the human host. There is a variety of cysteine proteases hence they are subdivided into families and in this study we focus on the clan CA, papain family C1 proteases. The current inhibitors for the protozoan cysteine proteases lack selectivity and specificity which contributes to drug toxicity. Therefore there is a need to identify the differences and similarities between the host, vector and protozoan proteases. This study uses a variety of bioinformatics tools to assess these differences and similarities. The Plasmodium cysteine protease FP-2 is the most characterized protease hence it was used as a reference to all the other proteases and its homologs were retrieved, aligned and the evolutionary relationships established. The homologs were also analysed for common motifs and the physicochemical properties determined which were validated using the Kruskal-Wallis test. These analyses revealed that the host and vector cathepsins share similar properties while the parasite cathepsins differ. At sub-site level sub-site 2 showed greater variations suggesting diverse ligand specificity within the proteases, a revelation that is vital in the design of antiprotozoan inhibitors.
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- Date Issued: 2015
Malarial drug targets cysteine proteases as hemoglobinases
- Authors: Mokoena, Fortunate
- Date: 2012
- Subjects: Malaria -- Chemotherapy , Antimalarials , Hemoglobin , Proteolytic enzymes , Cysteine proteinases , Plasmodium falciparum , Plasmodium vivax , Papain
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4005 , http://hdl.handle.net/10962/d1004065 , Malaria -- Chemotherapy , Antimalarials , Hemoglobin , Proteolytic enzymes , Cysteine proteinases , Plasmodium falciparum , Plasmodium vivax , Papain
- Description: Malaria has consistently been rated as the worst parasitic disease in the world. This disease affects an estimated 5 billion households annually. Malaria has a high mortality rate leading to distorted socio-economic development of the world at large. The major challenge pertaining to malaria is its continuous and rapid spread together with the emergence of drug resistance in Plasmodium species (vector agent of the disease). For this reason, researchers throughout the world are following new leads for possible drug targets and therefore, investigating ways of curbing the spread of the disease. Cysteine proteases have emerged as potential antimalarial chemotherapeutic targets. These particular proteases are found in all living organisms, Plasmodium cysteine proteases are known to degrade host hemoglobin during the life cycle of the parasite within the human host. The main objective of this study was to use various in silico methods to analyze the hemoglobinase function of cysteine proteases in P. falciparum and P. vivax. Falcipain-2 (FP2) of P. falciparum is the best characterized of these enzymes, it is a validated drug target. Both the three-dimensional structures of FP2 and its close homologue falcipain-3 (FP3) have been solved by the experimental technique X-ray crystallography. However, the homologue falcipain-2 (FP2’)’ and orthologues from P.vivax vivapain-2 (VP2) and vivapain-3 (VP3) have yet to be elucidated by experimental techniques. In an effort to achieve the principal goal of the study, homology models of the protein structures not already elucidated by experimental methods (FP2’, VP2 and VP3) were calculated using the well known spatial restraint program MODELLER. The derived models, FP2 and FP3 were docked to hemoglobin (their natural substrate). The protein-protein docking was done using the unbound docking program ZDOCK. The substrate-enzyme interactions were analyzed and amino acids involved in binding were observed. It is anticipated that the results obtained from the study will help focus inhibitor design for potential drugs against malaria. The residues found in both the P. falciparum and P. vivax cysteine proteases involved in hemoglobin binding have been identified and some of these are proposed to be the main focus for the design of a peptidomimetric inhibitor.
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- Date Issued: 2012
Structural analysis of prodomain inhibition of cysteine proteases in plasmodium species
- Authors: Njuguna, Joyce Njoki
- Date: 2012
- Subjects: Plasmodium , Cysteine proteinases , Proteolytic enzymes , Malaria -- Chemotherapy , Antimalarials , Plasmodium falciparum
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4021 , http://hdl.handle.net/10962/d1004081 , Plasmodium , Cysteine proteinases , Proteolytic enzymes , Malaria -- Chemotherapy , Antimalarials , Plasmodium falciparum
- Description: Plasmodium is a genus of parasites causing malaria, a virulent protozoan infection in humans resulting in over a million deaths annually. Treatment of malaria is increasingly limited by parasite resistance to available drugs. Hence, there is a need to identify new drug targets and authenticate antimalarial compounds that act on these targets. A relatively new therapeutic approach targets proteolytic enzymes responsible for parasite‟s invasion, rupture and hemoglobin degradation at the erythrocytic stage of infection. Cysteine proteases (CPs) are essential for these crucial roles in the intraerythrocytic parasite. CPs are a diverse group of enzymes subdivided into clans and further subdivided into families. Our interest is in Clan CA, papain family C1 proteases, whose members play numerous roles in human and parasitic metabolism. These proteases are produced as zymogens having an N-terminal extension known as the prodomain which regulates the protease activity by selectively inhibiting its active site, preventing substrate access. A Clan CA protease Falcipain-2 (FP-2) of Plasmodium falciparum is a validated drug target but little is known of its orthologs in other malarial Plasmodium species. This study uses various structural bioinformatics approaches to characterise the prodomain‟s regulatory effect in FP-2 and its orthologs in Plasmodium species (P. vivax, P. berghei, P. knowlesi, P. ovale, P. chabaudi and P. yoelii). This was in an effort to discover short peptides with essential residues to mimic the prodomain‟s inhibition of these proteases, as potential peptidomimetic therapeutic agents. Residues in the prodomain region that spans over the active site are most likely to interact with the subsite residues inhibiting the protease. Sequence analysis revealed conservation of residues in this region of Plasmodium proteases that differed significantly in human proteases. Further prediction of the 3D structure of these proteases by homology modelling allowed visualisation of these interactions revealing differences between parasite and human proteases which will lead to significant contribution in structure based malarial inhibitor design.
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- Date Issued: 2012