Biomedical subjects

V Kothekar

Publications and source records attributed to V Kothekar.

At least 19 recordsLinked to original sources

PubMed2004

Identification, expression, modeled structure and serological characterization of Plasmodium vivax histone 2B.

Histones play important role in DNA packaging, replication and gene expression. Here, we describe the isolation and characterization of histone 2B (PvH2B) gene from the most common but non-cultivable human malaria parasite Plasmodium vivax. The isolated cDNA clone of PvH2B was allowed to express in Escherichia coli and the recombinant protein was purified by affinity chromatography. The expressed PvH2B protein showed DNA-binding properties on the South-Western analysis and the confocal microscopy localized it in the parasite nucleus. This gene is actively expressed during blood stages of the parasite and all P. vivax patients produced antibodies against the protein. The mRNA of PvH2B was found to contain a poly(A) tail at its 3' end, unlike abundant mRNA of human H2B. The encoded polypeptide is 118 amino acid long contains a nuclear targeting site, a signature motif of H2B and showed 74% homology to its host molecule. The structure of PvH2B showed that it has certain differences from that of its host at critical functional sites (viz acetylation, methylation, trypsin cleavage, DNA-binding and inter-histone interaction) which are required for general gene expression and DNA packaging. The distinctive structural features of P. vivax H2B described here may help in designing the specific antimalarial drugs.

Amino Acid Sequence↗

PubMed2001

Computer modeling of small heat-shock metalloprotease of the human malaria parasite Plasmodium vivax.

We present here computer generated model of N-terminal fragment, amino acids (aa) 36-245, of a Plasmodium vivax heat shock metalloprotease called PVHSP28, whose gene was cloned and characterised earlier. The fragment showed homology with HSPs from many organisms, including Escherichia coli and Haemophilus influenzae. PVHSP28 had the signature sequence 'HEXXH' and 'EXXXD' of Zinc metalloproteases. Being the first malarial HSP possessing metalloprotease activity, PVHSP28 is an ideal target for the design of new anti-malarial drugs. However, except for a small region (aa 62-132) which had 24.6% sequence similarity with 1TAQ (a DNA polymerase), it did not show sequence similarity with any published structures in protein data bank. Hence it could not be modelled using any automated modeling programs. We modelled 36-245 aa of PVHSP28 using predicted secondary structure as well as experimentally determined and predicted properties of the protein on the basis of its amino acid sequence, using various Internet tools and in-house package MODEL. The model was energy minimised using Sander's module of AMBER 5.0, working on a Silicon Graphics machine, with all atom force field.

Amino Acid Sequence↗

PubMed2001

Computer aided study of ligand binding with catalytic domain of Avian sarcoma virus integrase and its ligand binding loops.

We have carried out 1 nanosecond (ns) Molecular Dynamics (MD) simulations of the drug Y3 (4-acetylamino-5-hydroxynaphthalene- 2, 7-disulfonic acid) complexed with catalytic domain of Avian sarcoma virus Integrase (ASV-IN), both in vacuum and in the presence of explicit solvent. Starting models were obtained on the basis of PDB co- ordinates (1A5X) of ASV-IN-Y3 complex. Mn(2+) cation was present in the active site. To neutralize the positive charge in the presence of explicit solvent, eight Cl(-)anions were added. Energy Minimization (EM) and MD simulations, for both the systems, were carried out using Sander's module of AMBER5.0 with all atom force field. We also carried out 1 ns MD simulation on two flexible loops--L1 (Gly54-Gln62) and L2 (Trp138-Met155) playing crucial role in interaction of IN with the drug, under differing environmental conditions (vacuum, aqueous and organic solvent methanol). Comparison of the conformational changes in the loops, monomer and dimer is presented in the paper. Our results showed that the conformation of the loop region was closest to crystallographic data in case of monomer and constrained loops in aqueous environment. However, the dimer in vacuum was more stable than monomer. The beta sheet structure of the monomer in aqueous environment was unstable. Latter also took long time for equilibration. The box formed by loops L1 and L2 from two sub units (IINA and INB) of the dimer satisfies prerequisites for ligand recognition site and seems to be the functional biological unit.

Amino Acid Sequence↗

PubMed2000

Enzyme selectivity of new cyclooxygenase-2/5 lipoxygenase inhibitors using molecular modeling approach.

We have studied the conformational flexibility of three 5-keto-substituted 7-tert-butyl-2,3-dihydro-3,3-dimethylbenzofurans (DHDMBFs) which show dual cyclooxygenase (COX) and 5-lipoxygenase (LOX) inhibition and are potential candidates as antiinflammatory agents and analgesics. The conformations were studied by systematic search, molecular mechanics (MM) and simulated annealing molecular dynamics (SAMD) techniques. We also studied several structure based parameters and distribution of molecular electrostatic potential (MEP) around these molecules. All the three compounds were docked in the active cavity of cyclooxygenase-2 (COX-2) using graphical and energy grid search techniques. The complex geometries were optimized by MM. The results on conformational flexibility, inter-atomic distances and angles, MEP distribution and points of contacts with peptide side chains in active cavity have been used to understand the mechanistic cause of differential action of these molecules.

Arachidonate 5-Lipoxygenase↗

PubMed1999

Computer simulation of the interaction of non-steroidal anti-inflammatory drugs: indoprofen and NS398 with cyclooxygenase.

We have applied computer simulation technique to study interaction of two anti-inflammatory drugs (NSAIDs) indoprofen and NS398 with cyclooxygenase (COX-1 and COX-2) enzymes. We have also investigated conformational flexibility of the two drugs by systematic search and simulated annealing molecular dynamics (SAMD) methods. Both the drugs were docked in the cyclooxygenase channel using in house docking program IMF1. The complexes were energy minimised by molecular mechanics (MM) method. These were heated for 30 picoseconds (ps), equilibrated for 110 ps at 300K and subjected to 'production simulation' for 110 ps by molecular dynamics (MD) method using Sanderís module of AMBER 5.0 package and united atom force field mostly from PARM96.DAT. Integration was carried out with time step of 0.001 ps, distance dependent di-electric constant with scaling factor 2.0 for 1-4 interaction and cut-off distance for non-bonded pair-list equal to 8A. The non-bonded pair-list was upgraded after every 20 cycles. The coordinate output from MD trajectories is analysed using analysis package of AMBER 5.0, MOLMOL, P-CURVES 3.0 and in house packages: ANALMD, ANALP1. We have observed perturbative changes in COX-1 and COX-2 structures due to indoprofen and NS398. In case of indoprofen specific changes between COX-1 and COX-2 were noted in helix D, H6, S6 and helix H8 in the cyclooxygenase cavity. In case of NS398 these were in helix B in membrane binding domain, helix H6, S8 and S10 in cyclooxygenase cavity and helices H14-H16 in small lobe close to haem binding region. Implications of these results in enzyme selectivity by NSAIDs is discussed here.

Anti-Inflammatory Agents, Non-Steroidal↗

PubMed1999

Theoretical study of conformational flexibility of tuftsin in vacuum and in aqueous environment.

Conformational flexibility of tuftsin molecule is studied using all-atom based atom-atom potential and systematic search, simulated annealing molecular dynamics (SAMD) and molecular dynamics (MD) techniques. Latter was carried out for 650 pico seconds (ps) using AMBER 4.0 with explicit water in TIP3P model. Number of inter-atomic distances and torsional angles were monitored during SAMD and MD simulation. We found that tuftsin molecule, irrespective of any starting conformation, assumes highly folded structure with strong electrostatic interaction between Lys-2 NH3 and Arg-4 carboxylic group and weak hydrogen bond between Lys-2 CO and Arg-4 NH atoms. It had distorted but stable conformation close to inverse gamma turn.

Amino Acid Sequence↗

PubMed1998

Molecular dynamics simulation of interaction of histone-like protein of mycobacterium tuberculosis (Hlpmt) and histone of clostridium pasteurianum (DBHclopa) with 35 based paired GC rich U-bend DNA.

Three dimensional structure of the first ninety two residues of histone like protein from Mycobacterium tuberculosis (Hlpmt) and histone of Clostridium pasteurianum (DBHclopa) are obtained here, on the basis of amino acid sequences of the two proteins, making use of secondary structure prediction programs, sequence search and HOMOLOGY based modeling tools available on Internet. The proteins were docked to a 35 base paired GC rich U bend DNA (U35DNA). Structures of proteins Hlpmt and DBHclopa; U35DNA; and complexes: Hlpmt-U35DNA and DBHclopa-U35DNA were optimized by molecular mechanics (MM) and simulated for 260 pico seconds (ps) in vacuum by molecular dynamics (MD) technique using AMBER 4.0 package with Cornell et al force field. The proteins, when simulated alone, showed compaction. DBHclopa showed larger compaction compared with Hlpmt. U35DNA when simulated alone straightened out and assumed a B-form. In the complexes, Hlpmt showed same order of compaction as in absence of DNA, while DBHclopa showed reduced compaction. In the presence of Hlpmt two ends of helicoidal axis of U35DNA came closer, but slightly out of plane, indicative of its role in overwinding and packaging double stranded DNA. DBHclopa did not give rise to DNA overwinding. The results show architectural role of Hlpmt and DBHclopa in DNA packaging and its sequence dependence.

Amino Acid Sequence↗

PubMed1998

Conformational flexibility of voltage gated dihydropyridine sensitive calcium channel in hydrated DMPC bilayer.

We have built a model for Ca2+ channel using amino acid sequence from S3 helix of the fourth internal repeat of alpha 1 subunit of dihydropyridine sensitive calcium channel from rabbit skeletal muscle, on the basis of X-ray crystallographic data on four helix bundle. The assembling of the geometry of the pore was achieved using a sixteen residues peptide fragment from short SSI/II loop (residues 1010-1025) which had F1013 and E1014 residues, considered to be important for the drug induced activity of the channel. This had hairpin bend between F1013 to W1016. The drug 2,6-dimethyl 3,5-dicarbomethoxy-4 (2-nitrobenzyl) 1,4 dihydropyridine (DHP) (nifedipine), which is a calcium channel inhibitor used in the treatment of cardiovascular diseases, was introduced, interacting with these two residues via Ca2+ ion. Two more Ca2+ ions were introduced in the pore. The model was incorporated in the bilayer of 36 dimyristoyl phosphatidyl choline (DMPC) molecules with 1201 water molecules and simulated for 200 picoseconds (ps) after equilibration for 120 ps. We also simulated the channel model in vacuum and in aqueous environment for comparison. The latter was unstable after 120 ps. The geometric parameters of the pore are analysed by MOLMOL, PCURVE 3.1 and a special program ANHELIX developed by us. Stability of the pore dimensions during simulations is discussed in this paper.

Amino Acid Sequence↗

PubMed1997

500 picosecond molecular dynamics simulation of amphiphilic polypeptide Ac(LKKL)4 NHEt with 1,2 di-mysristoyl-sn-glycero-3-phosphorylcholine (DMPC) molecules.

Molecular dynamics (MD) simulation of the interaction between amphiphilic polypeptide Ac(LKKL)4NHEt and 4 DMPC (1,2 di-mysristoyl-sn-glycero-3-phosphorylcholine) molecules has been carried out at 310 K for 500 picoseconds (ps) using AMBER 4.0. Interaction energy and a number of conformational parameters are calculated for the subaveraged coordinates, using P-CURVES 3.1 and our MD trajectory analysis program ANALMD. No significant change in DMPC headgroup conformation was observed. However, the mobility of P atoms was found to be restricted. The chains were quite flexible and their flexibility increased towards the ends. They interacted amongst themselves. The polypeptide remained predominantly in alpha-helical conformation. Leu1 and Lys2 at the N terminus and Leu13 to Leu16 at C terminus assumed non helical conformation and were quite flexible. Average interaction energy between the polypeptide and DMPC molecules was found to be -151.828 kcal*mol-1. The main contributory factor was electrostatic interaction of Lys NH3+ groups with the DMPC phosphates. On an average one Lys chain interacted with 1.5 DMPC molecules. Central region of the polypeptide had better contact with DMPC molecules. A model for the fusogenic properties of the polypeptide is presented on the basis of MD results.

Amino Acid Sequence↗

PubMed1996

Molecular dynamics simulation of conformational flexibility of alamethicin fragments in aqueous and membranous environment.

We present here results on molecular dynamics (MD) simulation on two fragments of channel forming antibiotic peptide Alamethicin, containing isoamino butyric acid (Aib). Simulations are carried out in aqueous and membranous environment in a bilayer of 39 molecules of Dimyristoyl phosphatidyl choline (DMPC). The peptides Boc-Pro-Aib-Ala-Aib-OBzl (Alam 1) and Boc-Leu-Aib-Pro-OBzl (Alam 2) were simulated from their crystallographic coordinates. The bilayers were built from two different conformations (A and B) of DMPC reported in crystal data. The P-N dipoles were arranged hexagonally with surface area per lipid molecule 66.5 A degrees 2 and P-P separation across the bilayer 34 A degrees. They were hydrated by 28.6 and 25.5 water molecules per DMPC molecule. Simulations are done using AMBER 4.0 package in constant number volume temperature (NVT) condition for 100 pico seconds (ps) in aqueous environment and 250 ps of equilibrated bilayer. Geometric parameters of lipids as: bilayer thickness, order parameter of the chains, transfraction of chain torsional angles were monitored. We also monitored geometric parameters of the peptides as backbone torsional angles, distances amongst C alpha atoms, angles between C alpha atoms, movement of center of gravity (CG) along and perpendicular to bilayer normal. We find that membrane bilayer is slightly disturbed due to the presence of peptides. In case of alam 2 in water angles phi 1 and phi 3 showed larger variation in water compared to same in the bilayer. The peptide conformation is more stable in DMPC bilayer. However the peptides showed movement along and perpendicular to bilayer normal. This we believe is due to hydrophobic nature of these peptides.

Alamethicin↗

PubMed1996

260 ps molecular dynamics simulation of substance P with hydrated dimyristoyl phosphatidyl choline bilayer.

We present here results on 260 pico seconds (ps) molecular dynamics (MD) simulation of substance P (SP) in hydrated bilayer of dimyristoyl phosphatidyl choline (DMPC) (39 molecules of DMPC with 776 water molecules). 260 ps MD simulation has been carried out in 0.001 ps time interval with united atom force field, using AMBER 4.0 package. Non bonded pair list was updated every 20 cycles using 12.5 Angstrom cut off distance. Analysis of MD data is done using our package ANALMD. The obtained models are presented using graphics package RASMOL. All simulations, analysis of MD data and graphics is done on INDIGO-2, R-4400 extreme graphics work station. Our results show no systematic change in order parameter, but reduction in transfraction of the chain torsional angles, compared to our earlier results on MD simulation on hydrated DMPC bilayer without SP. C-terminal and central peptide residues adopt partial helical conformation. Helix type as classified on the basis of H-bonds is between alpha and 3(10). The peptide backbone shows flexibility during heating runs. Later, it is stabilized and there was not much change in the spatial position of the backbone. Lipid matrix serves the role of immobilization of the peptide backbone in a preferred conformation.

Amino Acid Sequence↗

PubMed1996

Molecular dynamics simulation of hydrated phospholipid bilayers.

Understanding of microscopic behaviour of biological membrane is crucial for designing of molecules to control transport properties of the membranes. Phospholipid-water forms a good model system to study ligand induced structural and dynamical changes in membrane. The review has its main focus on molecular dynamics (MD) simulation of phospholipid bilayers. A brief summary of the current status of structure of phospholipid membranes based on different physico-chemical measurements is given. We discuss here mainly results of MD simulations in the recent years on hydrated phospholipid bilayers and their interaction with ligands. Simulation parameters as: choice of initial system, force fields, protocols for simulation are compared. Main results on: order parameter, head group and chain conformation, water penetration profile, chain tilts, pair-correlation function between atoms of lipid and water, diffusion of ions and ligands are discussed. The review gives application and limitation of MD method for studying lipid water system.

Computer Simulation↗

PubMed1994

200 picosecond molecular dynamics simulation of interaction of nifedipine with 1-2 dimyristoyl phosphatidylcholine membrane.

Interaction of calcium channel antagonist nifedipine (Nif) with 1-2 dimyristoyl phosphatidylcholine (DMPC) membrane has been studied using molecular dynamics approach. The simulations for one molecule of nifedipine with four DMPC molecules were carried out for 200 pico seconds (ps) using AMBER (Assisted Model Building with Energy Refinement) 3.0 adopted to CYBER 180/930 computer and changes in the structural parameters of DMPC were compared with those for DMPC monolayer (a matrix of nine molecules) optimized separately. Dynamics simulations for the latter had been carried for 40 ps. Our results show that the drug molecule (Nif) penetrates a discrete depth within the phospholipid matrix causing hydrocarbon chains of lipid molecules to swing that makes enough room for the receptor adjacent to the drug molecule.

Computer Simulation↗

PubMed1993

Computer stimulation of interaction of deacylcortivazol with d(TGTTCT)2.

We have obtained models for the interaction of deacylcortivazol (DAC) with the hexanucleotide duplex d(TGTTCT)2 (DNA) by computer simulation technique. The drug was made to interact with the DNA in the major groove and by intercalation mode. It was observed that the classical intercalation model with the drug sitting "end on" between base pairs was not possible. Major groove binding and partial intercalation were the two possible models. In the latter case, the drug enters between base pairs in the "head on" position. The relative merits of these two models vis-à-vis effectiveness of DAC are discussed in the paper.

Drug Interactions↗

PubMed1992

Transcription regulation by steroid hormones: a computer simulation study.

Three-dimensional structures of complexes of 66 amino acid-DNA binding domains of human progesterone (hPR), estrogen (hER) and glucocorticoid (hGR) receptors (proteins), with ten base pair DNA duplexes: d(AGGTCATGCT).d(AGCATGACCT) and d(AGAACATGCT).d(AGCATGTTCT) were obtained using computer modeling and molecular mechanics techniques. Cartesian coordinates for the proteins were obtained from: 1) structural data of hER and hGR by NMR spectroscopy; 2) steric constraints imposed by tetrahedral coordination of the zinc ion to Cys residues, and 3) energy minimization in torsional and cartesian space. The proteins were made to interact with DNA (in B-form) in major groove through alpha-helical linker between the two zinc fingers. The geometry of the complexes was obtained by allowing them to slide, glide, penetrate in to and out of the groove, and to rotate about the helical axis. The complexes were energy minimized. Also maximized was the number of H-bonds between proteins and DNA. The complex structures were refined by molecular mechanics using AMBER 3.0. Structural parameters of DNA were analyzed in each complex and compared with those of native DNA optimized separately. The stereochemical differences of the complexes are discussed.

Amino Acid Sequence↗

PubMed1992

Molecular mechanics simulation of the interaction of estrogen receptor with estrogen regulatory element.

A model for the interaction of 31 amino acid fragment (protein) from DNA binding domain of human estrogen receptor (hER) with a five base pair DNA sequence 5'GGTCA 3' from estrogen regulatory element (ERE) has been obtained using a step-wise procedure based on structural data on model peptides, DNA binding domain of hER, steric constrains imposed by tetrahedral coordination of the Cys sulphurs with zinc ion and classical secondary structural elements. Structure of the protein as well as its complex with DNA is obtained by energy minimization followed by refinement by molecular mechanics. The complex is stabilized by H-bonds between Lys22, Lys26 and Arg27 with DNA bases G2, T3 and T6. Lys22 also made H-bond with the backbone of G2. The backbone of Cys18 H-bonded with N7 of G1. DNA was in distorted B form and showed evidence of protein-induced conformational changes.

Amino Acid Sequence↗

PubMed1992

Computer aided study of the interaction of thyroid hormone receptor with DNA.

Interaction of the first zinc finger from human thyroid hormone receptor (finger) with hexanucleotide duplex d(AGGTCA).d(TGACCT) from thyroid regulatory element has been studied by molecular mechanics simulation technique. The structure of the finger as well as its complex with DNA is optimized using constrain of tetrahedral coordination of the zinc ion to Cys sulphurs. The finger is stabilized by series of H--bonds (5 in backbone, 2 in side chains and 2 between backbone and side chains). The complex is stabilized by H-bonds between side chains of Tyr 11, His 12, Tyr 13 and Arg 14 with G2, G3 and G8. DNA is in B form. H--bonding network within DNA is preserved. Opposite strand P-P and Cl'-Cl' distances are changed slightly. There is a systematic change in the backbone torsional angles and sugar pucker. Also, there is an evidence of protein-induced conformational change in DNA.

Amino Acid Sequence↗

PubMed1992

Stereochemical aspects of interaction of DNA binding domain of human progesterone receptor with d(AGGTCATGCT)2.

Structures of (i) 66 amino-acid fragment (residues 567-633) from DNA binding domain of human progesterone receptor (hPR), (ii) a ten base pair DNA sequence d(AGGTCATGCT)2 from hormone responsive element (HRE) and (iii) a complex of these two are optimised by computer modelling and molecular mechanics technique using extensive steric constraints from secondary structure predictions, comparison with the structures of known metalloproteins, geometric constraints imposed by tetrahedral coordination with the zinc ion and comparison with structures of DNA binding domains of human glucocorticoid and estrogen receptors (hGR and hER). Structure of the complex was obtained using genetic modification data on steroid receptors and general consensus about protein-DNA interaction. DNA is in distorted B conformation. Sequence dependent as well as protein-induced conformation changes are noticed. There is change in propeller twist, buckle and angle between glycosyl bonds. However, H-bonding network is preserved. The complex is stabilized with eighteen hydrogen-bonds, mainly between peptide side-chains and backbone phosphate. There are five specific H-bonds between basic amino acid side chains, Lys 22, Lys 26 and Arg 27, and DNA bases, A1, G3, G16 and A17. Gly 19, Ser 20 and Val 23 are in close proximity of DNA.

Amino Acid Sequence↗