Phytoconstituents Obtained from Tanzanian Medicinal Plants Display a High Potential to Inhibit Glucosamine-6-Phosphate Synthase As an Antimicrobial Target
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Journal of Biological Engineering Research and Review 2017; 4(1): 20-33 CODEN: JBERA9 ISSN: 2349-3232 SBEWS Available online at www.biologicalengineering.in/Archive Research Article Phytoconstituents obtained from Tanzanian medicinal plants display a high potential to inhibit Glucosamine-6-phosphate synthase as an antimicrobial target Tomisin Happy Ogunwa 1Centre for Biocomputing and Drug Development, Adekunle Ajasin University, Akungba-Akoko, Ondo State, Nigeria. 2Department of Biochemistry, Adekunle Ajasin University, Akungba-Akoko, Ondo State, Nigeria. *Email: [email protected]; [email protected] ARTICLE INFO: Article History: Abstract: Recent pharmacological research has focused attention on biological properties of bioactive Received: 16/07/2017 compounds derived from medicinal plants. With the aid of in silico modeling and Revised: 05/09/2017 computational studies, the possible antimicrobial activity of phytoconstituents isolated from various Accepted: 11/09/2017 Available Online: 11/10/2017 Tanzanian medicinal plants was investigated. Out of the eighteen compounds selected and docked against a critical antimicrobial target, Glucosamine-6-phosphate synthase from Escherichia coli (E. Coli), Keywords: eight (8) compounds including baphikinone, annonaine, rheediaxanthone B, isorheediaxanthone, Medicinal plants, antimicrobial, forbexanthone, amaniensine, 12-hydroxy-des-D-garcigerrin A and baphikixanthone showed high Glucosamine-6-phosphate synthase, binding affinity towards the enzyme. The molecular interaction, in comparison with the reference molecular interaction, docking compounds, fructose-6-phosphate and fluconazole revealed that the compounds favorably docked on the binding site and the enzyme-ligand complex possessed low binding energy value, implying that Copyright: © 2017 Ogunwa the compounds may be potent inhibitors of the enzyme. The binding energy values obtained ranged from T.H. This is an open access -7.0 kcal/mol to -9.3 kcal/mol compared to -7.6 kcal/mol and -6.0 kcal/mol obtained for article distributed under the fluconazole and fructose-6-phosphate respectively. The compounds penetrated and appeared to terms of the Creative Commons completely blocked the active site and, engaged amino acid residues at the active site in strong Attribution License (CC BY 4.0). hydrogen bonds. These residues include Val-399, Thre-352, Glu-488, Ser-349, Gln-348, Thre-302, Ala- 602, Lys-603, and Ser-303 most of which are required for catalytic activity. Hydrophobic interaction Citation: Ogunwa T.H. Phyto- also seemed to participate in stabilizing the enzyme-ligand complex. Overall, the binding affinity and constituents obtained from configuration for the selected phytoconstituents were comparable to the control ligands. Hence, the Tanzanian medicinal plants compounds may competitively hinder the synthesis of glucosamine-6-phosphate that is required for display a high potential to bacterial and fungal cell wall production. The results obtained in this study validate the inhibit Glucosamine-6- antimicrobial potential of the medicinal plant sources of the compounds and show that they possess phosphate synthase as an the ability to inhibit glucosamine-6-phosphate synthase as a target while providing insights into antimicrobial target. Journal of the possible molecular interaction involved in the antimicrobial effects observed in earlier reported Biological Engineering Research wet experiments. and Review. 2017, 4(1), 20-33 INTRODUCTION of pathogenic microorganisms to current antibiotics, anxiolytics, hypnotics, anticonvulsants, and sedatives is rapidly becoming the first challenge worldwide. The abuse he Glucosamine-6-phosphate synthase (GlmS), an T of available synthetic antibiotics is a contributory factor enzyme that plays a key role in the synthesis of the to the increased incidence of microbial resistance to bacterial and fungal cell wall, has become a potential present day antibacterial and antifungal drugs. Meanwhile, clinical target for antibacterial and antifungal drug prime and opportunistic bacterial and fungal infections are discovery [1, 2]. The enzyme catalyzes a reaction between observed on an increasing trend because of the increased fructose-6-phosphate (F6P) and L- glutamine to number of immune-compromised patients [6]. One of the generate glucosamine-6-phosphate that results in the essential ways of combating this new challenge is to production of UDP-N acetylglucosamine which is an discover novel and structurally diverse antibiotic essential component in building the peptidoglycan layer of compounds preferably from natural sources considering bacterial and fungal cell walls [2, 3]. Thus, inhibition of this their reduced toxicity and side effects [3, 7, 8]. Although enzyme with chemical compounds will eventually result it is a fact that the enzyme is also found in mammals, there in the death of bacteria and fungi [4]. Therefore, it is not are substantial variations in physiological surprising to observe that some GlmS inhibitors both consequences of GlmS inhibition between from natural or synthetic origin possess bactericidal or microorganisms and mammals which form a stable fungicidal properties [5]. On the other hand, the resistance 20 molecular basis for selectivity in action and toxicity of In Tanzania, diverse group of compounds such as specific enzyme inhibitors [9]. lactones, flavonoids, alkaloids, coumarins, limonoids, To date, medicinal plants have proved to be a rich terpenoids, benzophenones, xanthones and other source of promising and exciting structures for drug compounds has been obtained from available medicinal discovery [8]. Some medicinal plants are known to possess plants. The plant species include Baphia spp, Garcinia spp, pharmacological abilities to combat disease-causing Annona spp, Mammea spp, Teclea spp, Harrisonia spp, pathogens [10, 11]. For decades, various plant extracts etc. The reported biological properties of these plants are were studied for their antimicrobial properties against antioxidant, antimicrobial, anti-HIV, antimalarial, microorganisms such as bacteria (Escherichia coli, anticancer, antifungal and larvicidal activities. The extracts Staphylococcus aureus, Streptococcus spp, Klebsiella of these plants are said to exhibit significant activities pneumonia, etc.) and some common fungi (Candida albicans against a wide range of microorganisms [15]. Although the and Aspergillus niger). Recently, the phytochemicals from antimicrobial capacities of the extracts of these plants have such plant extracts with antifungal and antibacterial been reported in in vitro experiments, the target and effects have been isolated and characterized [12-14]. molecular mechanism of such properties remained Hence, attention has been diverted to studying their unknown. Therefore, this research was done to elucidate biological effect for various beneficial clinical and the possible molecular basis of antimicrobial effects of therapeutic applications. selected compounds previously isolated from the Tanzanian medicinal plants. Table 1. Selected phytoconstituents used as ligand in this study and their plant source S/No Name Structure Plant source Plants Reference part 1 Annonaine Annona Leaves 15, 16 Squamosal 2 Tecleamaniensine B Teclea Stem 17 amanuensis 3 Amaniensine Teclea Stem 17 amanuensis 4 Baphikixanthones A Baphia kirkii Stem 18 21 5 Baphikixanthones B Baphia kirkii Stem 18 6 Baphikixanthones C Baphia kirkii Stem 18 7 Baphikinone Baphia kirkii Stem 18 8 Garceduxanthone Garcinia Root 19 edulis 9 Forbexanthone Garcinia Root 19 edulis 10 Isorheediaxanthone B Garcinia Stem 20, 21, 22 volkensis 11 12-hydro-des-D- Garcinia Stem 23 garcigerrin A volkensis, Garcinia livingstonei 22 12 Rheediaxanthone B Garcinia Stem 22, 24, 25 volkensis 13 3-hydroxy-5-methoxy Allanblackia Stem 26, 27, 28 biphenyl ulugurensis 14 3-Methoxy-8,9-methy Baphia Root 15 lenedioxypterocarpene puguensis 15 4-hydroxy-3-methoxy Baphia Root 29 cinnamate puguensis 16 Puguflavanone A Baphia Root 29 puguensis 17 Puguflavanone B Baphia Root 29 puguensis 18 Erythrisenegalone Baphia Root 29, 30, 31 puguensis, Erythrina fusca 23 METHODS structure of GlmS. All water molecules and ligand crystallized with the proteins were deleted before molecular Preparation of ligands docking procedures. A total of twenty (20) ligands used for docking study were selected from the literature [15]. Out of these compounds, Evaluation and validation of the model eighteen (18) were phytochemicals isolated from various The modeled enzyme was assessed by procheck for medicinal plants found in Tanzania while the other two (2) structural analysis. The Ramachandran plot and Z score ligands were fluconazole (a synthetic compound) and values were generated using the protein structure and model fructose-6-phosphate (natural ligand) which were used as assessment tools of Pdbsum database of the European reference compounds (Table 1). The chemical structure of Bioinformatics Institute (EMBL-EBI) these compounds was obtained from NCBI PubChem (http://www.ebi.ac.uk/) and the Swiss-Model workspace compound database (http://swissmodel.expasy.org). The protein structure was (http://www.ncbi.nlm.nih.gov/pccompound) and prepared also loaded on ProQ web server to evaluate the PDB using Marvinsketch. Three-dimensional (3D) optimizations structure [32, 33]. The values for LG-score, Maxsub, as well of the ligand structures were done before use in docking as Qmean score, were obtained. studies. The 3D structure of the ligands was saved as MOL SD format after