Journal of Applied Biology & Biotechnology Vol. 8(02), pp. 12-21, March-April, 2020 Available online at http://www.jabonline.in DOI: 10.7324/JABB.2020.80203

Comparative modeling of sodium- and chloride-dependent GABA transporter 1 and docking studies with natural compounds

Nitya Bankupalli, Shravan Kumar Gunda*, Mahmood Shaik Bioinformatics Division, PGRRCDE, Osmania University, Hyderabad 500007, India

ARTICLE INFO ABSTRACT

Article history: is a chronic neurological disorder that causes uncontrolled seizures which can affect the body Received on: August 20, 2019 physically and psychologically. When a person experiences seizure, it is very difficult for them to breathe and Accepted on: October 11, 2019 they bite their tongue as a reflex. Glutamatergic and gamma-aminobutyric acid ergic (GABAergic) transmission Available online: March 26, 2020 in the brain causes seizures. The immature brain is more prone to seizures than the adult brain. Gene SLC6A1 produces GABA1 protein which helps in reuptake of GABA from the synapse. Presently in this study, protein modeling and molecular docking were performed on protein sequence sodium- and chloride-dependent GABA Key words: transporter 1 that was retrieved from uniport. MODELLER 9.21 versions were used to develop a homology Epilepsy, GABA1, homology model. X-ray structure of Drosophila dopamine transporter in complex with cocaine (4XP4) from species modeling, natural compounds, Drosophila melanogaster was used as a template. Autodock4.2, a docking software, was used for molecular docking docking studies. Against the modeled protein, 22 natural compounds were docked. According to the results, natural compounds like Morusin showed high binding energy against modeled protein than standard .

1. INTRODUCTION numbness, memory lapses, jerking movements, sweating, biting About 70 million people around the globe suffer from epilepsy of the tongue, difficulty in breathing, and the physical injuries that and 12 million reside from India [1]. Epilepsy exists as a chronic they may face during seizures are broken bones and uncontrolled disorder causing unpredictable, recurrent seizures that have a serious bladder [5]. Many pieces of evidence have proved that acquired effect on mental and physical functions. Seizures are expressed are influenced by the genetic effect [6]. Symptomatic when there is an accumulation of multiple caused due to epilepsies are proven to show changes in the epileptic brain. The neurons over activity which are released rhythmically [2]. Due to variations that are developed are altered dendritic morphology, an imbalance transmission between excitatory glutamatergic and dysplastic neurons, and electrophysical evidence of abnormal inhibitory gamma-aminobutyric acid ergic (GABAergic), seizures synchronization and abnormal networks [7]. are caused [3]. Usually rather than the adult brain, the immature SLC6A1 encodes GAT1 protein. It is a voltage-dependent GABA brain is more susceptible to seizures. These development transporter that is responsible for the reuptake of GABA from processes are influenced by synaptic reduction, change in density the synapse [8]. GABA is a main inhibitory that of neurotransmitter receptors, modification of GABAA receptor counters balance neuronal excitation in the brain and is directly or activity from an immature brain to mature nervous system and responsible for the regulation of muscles. Any disruption in structure, and changes in the function of glutamate receptors [4]. regulation can cause seizures [9]. In a few studies, findings suggest Before the occurrence of seizures, few people experience different that SLC6A1 can cause specific epilepsy syndrome myoclonic- feelings, sensations, and changes in behavior. Some general astatic epilepsy that causes early abnormal development. These symptoms that epilepsy patients endure are loss of consciousness, abnormalities can be caused due to GAT1 GABA transport [10]. The study aims were to explain the silico modeling of the low sodium-dependent dopamine transporter. The 3D model was *Corresponding Author generated by using MODELLER 9.21 modeling software and Shravan Kumar Gunda, Bioinformatics Division, PGRRCDE, Osmania was validated by using Procheck. By using autodock4.2, protein- University, Hyderabad 500007, India. E-mail: [email protected] ligand binding studies were carried out on modeled protein.

© 2020 Gunda, et al. This is an open access article distributed under the terms of the Creative Commons Attribution License -NonCommercial-ShareAlike Unported License (http://creativecommons.org/licenses/by-nc-sa/3.0/). Gunda, et al.: Comparative modeling of sodium- and chloride-dependent GABA transporter 1 and docking studies 13 with natural compounds 2020;8(02):12-21 2. METHODOLOGY energy function was applied. The modeled Solute carrier family Homology modeling also known as comparative study of protein 2, facilitated glucose transporter member protein was loaded and is used to build a target molecule from the unknown sequence by hydrogens were added and saved in PDBQT format. Subsequently, an online tool of Basic Local Alignment Search Tool (BLAST) the ligand was loaded and conformations were set and saved in search. Homologs are found during this analysis with the help PDBQT format. AutoGrid was used for selecting and calculating of the BLAST, which helps to find the homology sequence of grid parameters. A grid-point spacing of 0.375 Å was applied the target in the template. The BLAST analysis shows sequence and a grid map with 60 × 60 × 60 points was used for all the similarities and identities of the target with the template [11]. dockings. Coordinates X, Y, and Z were taken on the basis of the Finally, the protein is created for further computational analysis. amino acids present in the active site predicted in the Sybyl6.7 Sodium- and chloride-dependent GABA transporter 1 (Uniprot biopolymer module. To run the Autodock, default parameters were accession number: P30531) were taken from species Homo sapiens used [20–22]. which was retrieved from the UniProtKB database. To select the template, a search was performed in BLAST [12]. X-ray structure 4. RESULTS AND DISCUSSION of Drosophila dopamine transporter in complex with cocaine (4XP4) from species Drosophila melanogaster was selected. Using 4.1. Homology Modeling and Model Evaluation Modeller 9.21, three-dimensional structures were generated. Then The current study reports that the template protein (PDB ID: respective templates were retrieved from protein databases like 4XP4) having a high degree of homology with P30531 protein Protein Data Bank (PDB). While choosing the template, we should was used as a template with a good atomic resolution of its crystal consider the sequence identity and resolution of the template. If the structure. The target sequence sodium- and chloride-dependent parameters are high, it would be good enough to allow structural GABA transporter 1 (Uniport accession number: P30531) was and functional research in the resulting model [13]. retrieved from Homo sapiens species having 599 amino acids. By using BLAST, the template model PDB ID 4XP4 was identified To produce an adequate model, MODELLER 9.21 was used which and then the structure was modeled using Modeller9.21. The is an automated approach to homology modeling by appropriate generated structure was checked using the protein structure and spatial restraints [14]. By using Sequence alignments, protein and by PROCHECK. The secondary structure of the modeled protein template sequences were carried out using platforms like ClustalX is shown in Figure 2 and the Ramachandran plot is shown in and ClustalW is shown in Figure 1 [15]. The homology models of Figure 4. By using SPDBV, RMSD was calculated for template and the selected protein were constructed using modeler programs like generated model. Both the models were loaded and superimposed MODELLER 9.21. After manual reviewing of the alignment, the using the alpha carbon and RMSD was calculated. RMSD value input file in MODELLER 9.21 has to match the query and template was 0.79 Å, which shows that the generated model has a similarity sequence, 20 models were generated [16,17]. The lowest value of to the template (Fig. 3). the Modeller Objective Function is decided as the best model. Software like PROCHECK analyzes the stereochemical quality of the specific model and which can be used for further structural 4.2. Molecular Docking Results or functional study. PROCHECK develops a Ramachandran plot The ultimate goal of molecular docking was used for calculation which explains each residue organizing the in-depth calculation of the protein–ligand interactions. It is an efficient method to of Psi/Phi angles and the backbone conformation of the models. predict potential ligand interactions. In this study, the native The root mean square deviation (RMSD) was calculated by plant secondary metabolites (ligands) have been identified as superimposing (4XP4) specific model to access the accuracy and Solute carrier family 2, facilitated glucose transporter members’ reliability by using SPDBV [18,19]. inhibitors. To assign the best binding conformation, AutoDock4.2 uses (genetic algorithm) binding free energy assessment. 3. DOCKING METHODOLOGY Additionally, the activity of docked ligand molecules was compared with the standard drugs which were used as controls. 3.1. Active Site Identification A total of 22 natural compounds were docked against modeled The active site prediction was conducted in Tripo’s Sybyl 6.7. GABA transporter. It showed three active site pockets. The amino acids present in Among them, Morusin and Gallocatechin showed good one pocket are Leu136, Tyr139, Tyr140, Gln291, Phe294, Ser295 interactions and lower free energy values, indicating them to be Tyr296, Leu300, Ser396, Ala455, Ser456, Leu460, Tyr60, Ala61, more favored thermodynamically. When compared with standard Gly63, Gly65, and Asn66. drugs, i.e., Seletracetam, Carisbamate, Brivaracetum, and A total of 22 natural compounds were retrieved from NCBI. Valrocemide, Morusin exhibited the highest binding energy. In Using Sybyl 6.7, all the molecules were sketched and minimized Table 1 and Figure 5, the natural compounds were described with by adding Gasteiger–Huckel charges which are then saved in their corresponding interactions and binding energies. While the mol2 format. Molecular docking studies were executed on all standard drugs which were used as controls were represented with the natural compounds separately by using the AutoDock4.2 their corresponding interactions and binding energies in Table 2 program, Lamarckian Genetic Algorithm, and empirical free and Figure 6. 14 Gunda, et al.: Journal of Applied Biology & Biotechnology 2020;8(02):12-21

Figure 1: Alignment sequence of sodium- and chloride-dependent GABA transporter 1 and template 4XP4.

Figure 2: The cartoon model of sodium- and chloride-dependent GABA Figure 3: Superimposed model of sodium- and chloride-dependent GABA transporter 1(P30531). transporter 1 (P30531) and template protein (4XP4). Gunda, et al.: Comparative modeling of sodium- and chloride-dependent GABA transporter 1 and docking studies 15 with natural compounds 2020;8(02):12-21

Figure 4: Ramachandran plot of the modeled protein sodium- and chloride-dependent GABA transporter 1(P30531) exhibited 93.1% amino acid residues in the most favored region. In the allowed region, there are 33 amino acid residues present and there are no residues in the disallowed region. 16 Gunda, et al.: Journal of Applied Biology & Biotechnology 2020;8(02):12-21

Table 1: Protein–ligand interactions, binding energy of 22 natural compounds with the modeled protein. Binding energy ΔG Dissociation constant S.no Compound name Interacting amino acids (Kcal/Mol) (kI) (µM) 1 Quercetin Phe294, Tyr39, Ile60, Ala61 −7.18 −5.48 2 Chrysin Tyr140,Ser396 −6.80 −10.38 3 Kaempferol Ser456, Ala61, Tyr60 −6.40 −20.25 4 Myricetin Try140, Ala61, Gly63, Asp451, Ser456 −6.63 −13.92 5 Genistein Ala455, Asp451, Ser295 −6.53 −16.24 6 Daidzein Ser295, Asp451, Ser456 −6.83 −9.84 7 Genistin Ser359, Srg69, Phy294, Leu 460, Ser456 −4.81 −300.1 8 Daidzin Ser295 (3), Leu132 −5.88 −48.67 9 Morusin Trp68, Tyr140, Ser396, Leu298 −8.23 −927.15 10 Apigenin Try60, Asp451, Gly65, Ser456 −6.68 −12.65 11 Ellagic acid Ala61, Ser295, Ser456,Leu460 −7.18 −5.5 12 Resveratrol Ala61, Gly297 −6.37 −21.35 13 Pelargonidin Phe294, Asp451, Ala61, Ser295 −6.61 14.23 14 Cyanidin Try140, Ala61, Gly65, Gln291(2) −6.69 12.55 15 Acacetin Try60, Try140 −6.22 27.52 16 Quinic acid Gly65, Ala61 −5.04 201.24 17 Gallocatechin Asn66, Ser 295, Gly65 −7.33 4.21 18 Hesperitine Ser295 −6.25 26.2 19 Valoneic acid Gly65, Try140, Try60, Try 139, Asp451, Gly457 −5.24 143.39 20 Pyrogallol Gly 65, Ala61, Asn66 −4.17 880.59 21 Corilagin Asp 451, Gln 291, Gly65, Try140 −7.18 5.48 22 Rutin Asp451, Try60, Ala61 −7.08 6.51

Continued Gunda, et al.: Comparative modeling of sodium- and chloride-dependent GABA transporter 1 and docking studies 17 with natural compounds 2020;8(02):12-21

Continued 18 Gunda, et al.: Journal of Applied Biology & Biotechnology 2020;8(02):12-21

Continued Gunda, et al.: Comparative modeling of sodium- and chloride-dependent GABA transporter 1 and docking studies 19 with natural compounds 2020;8(02):12-21

Figure 5: Molecular docking interactions of 22 natural compounds against GABA protein (numbers are the same as Table 1). 20 Gunda, et al.: Journal of Applied Biology & Biotechnology 2020;8(02):12-21

Table 2: Protein–ligand interactions, with binding energy of four standard drugs. S.No. Standard drugs Interacting amino acids Binding energy ΔG Dissociation constant (kI) (µM) (Kcal/Mol) 1 Seletracetam Gly63, Try140 −5.51 91.98 2 Carisbamate Ala61, Gly65, Try60 −5.72 63.79 3 Brivaracetum Ser396, Try140 −5.88 48.81 4 Valrocemide Try60, Gly296, Leu298 −5.61 77.62

Figure 6: Molecular docking interactions of four standard drugs (numbers are the same as Table 1). Gunda, et al.: Comparative modeling of sodium- and chloride-dependent GABA transporter 1 and docking studies 21 with natural compounds 2020;8(02):12-21 5. CONCLUSION 10. Treiman DM, GABAergic mechanisms in epilepsy. Epilepsia For the study of Epilepsy mechanisms, sodium- and chloride- 2001;42(3):8–12. 11. Patrick T, Clifford JT. Deep homology in the age of next- dependent GABA transporter 1 protein could be a potential target. generation sequencing. Philos Trans R Soc Lond B Biol Sci Protein modeling and molecular docking studies were performed 2017;372(1713):20150475. on sodium- and chloride-dependent GABA transporter 1 protein 12. Eswar N, John B, Mirkovic N, Fiser A, Ilyin VA, Pieper U, et al. Tools (SLC6A1). The modeled protein showed more than 90% of amino for comparative protein structure modeling and analysis. Nucleic acid residues in the core region and molecular docking studies Acids Res 2003;31(13):3375–80. showed good binding energy and interactions with modeled 13. Laskowski R, Jabłońska J, Pravda L, Vařeková RS, Thornton protein when compared to already existing drugs. The study JM. PDBsum: structural summaries of PDB entries. Protein Sci 2018;27(1):129–34. indicates natural compounds may be useful for the potential 14. Bohnuud T, Luo L, Wodak SJ, Bonvin AM, Weng Z, Vajda S, et.al. candidates for the treatment of epilepsy. With more enhanced drug A benchmark testing ground for integrating homology modeling and designing, we could have more natural drugs which could be a protein docking. Proteins 2017;85(1):10–6. wise treatment for epilepsy. 15. Larkin MA, Blackshields G, Brown NP, Chenna R, McGettigan PA, McWilliam H, et al. Clustal W and Clustal X version 2.0. Bioinformatics. 2007;23:2947–48. CONFLICT OF INTEREST 16. Rowan H, David KB, Michael G, Ozlem TB. PRIMO: an interactive None homology modeling Pipeline. PLoS One 2016;11(11):e0166698 17. Muhammad WS, Adeel R, Nazia N, Ahmed AQ, Nisar A. Homology modeling and docking analysis of ßC1 protein encoded by Cotton REFERENCES leaf curl Multan betasatellite with different plant flavonoids. Heliyon 1. Amudhan S, Gururaj G, Satishchandra P. Epilepsy in India 2019;5(3):e01303. I: epidemiology and public health. Ann Indian Acad Neurol 18. Thompson JD, Gibson TJ, Higgins DG. Multiple sequence alignment 2015;18(3):263–77. using ClustalW and ClustalX, current protocol in bioinformatics. Curr 2. Liao J, Tian X, Wang H, Xiao Z. Epilepsy and migraine—are they Protoc Bioinformatics 2002;2.3.1–2.3.22. comorbidity? Gen Dis 2018;5(2):112–8. 19. Bhattacharya A, Tejero R, Montelione GT. Evaluating protein 3. Fisher RS, Van Emde BW, Blume W, Elger C, Genton P, Lee structures determined by structural genomics consortia. Proteins P. Epileptic seizures and epilepsy: definitions proposed by the 2007;66(4):778–95. International League against Epilepsy (ILAE) and the International 20. Schwede T, Kopp J, Guex N, Peitsch MC. SWISS-MODEL: an Bureau for Epilepsy (IBE). Epilepsia 2005;46(4):470–2. automated protein homology-modeling server. Nucleic Acids Res 4. Sanchez RM, Jensen FE, Maturational aspects of epilepsy mechanisms 2003;31(13):3381–5. and consequences for the immature brain. Epilepsia 2001;42(5):577– 21. El-Hachem N, Haibe-Kains B, Khalil A, Kobeissy FH, Nemer G. 85. AutoDock and AutoDockTools for protein-ligand docking: beta-site 5. Robert SF, Acevedo S, Arzimanoglou A, Bogacz A, Helen JC. A amyloid precursor protein cleaving enzyme 1(BACE1) as a case study. practical clinical definition of epilepsy. Epilepsia 2014;55(4):475–82. Methods Mol Biol 2017;1598:391–403. 6. Berkovic SF, Andermann F, Andermann E, Gloor P. Concepts of 22. Nataraj SP, Khajamohiddin S, Jack T. Software for molecular docking: absence epilepsies: discrete syndromes or biological continuum. a review. Biophys Rev 2017;9(2):91–102. Neurology 1987;37(6):993–1000. 7. Armstrong DD. The neuropathology of temporal lobe epilepsy. J Neuropathol Exp Neurol 1993;52(5):433–43. 8. Durkin MM, Smith KE, Borden LA, Weinshank RL, Branchek TA, Gustafson EL. Localization of messenger RNAs encoding three How to cite this article: GABA transporters in rat brain: an in situ hybridization study. Mol Brain Res 1995;33(1):7–21. Gunda SK, Bankupalli N, Shaik M. Comparative modeling 9. Carvill GL, McMahon JM, Schneider A, Zemel M, Myers CT, Saykally of sodium- and chloride-dependent GABA transporter 1 and J, et al. Mutations in the GABA transporter SLC6A1 cause epilepsy docking studies with natural compounds. J Appl Biol Biotech with myoclonic-atonic seizures. Am J Human Genet 2015;96(5): 2020;8(02):12–21. DOI: 10.7324/JABB.2020.80203 808–15.