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N Pattabiraman

Publications and source records attributed to N Pattabiraman.

At least 37 records · Page 2Linked to original sources
PubMed1991

Crepe-ribbon representation for protein structures: comparison of phospholipases A2.

We describe a method to generate a novel representation for protein structures called "crepe ribbons." In our representation, each piece of the ribbon was constructed using the coordinates of the backbone atoms of each individual residue. Using the internal geometries of each residue and a helix-generating algorithm, a local origin and the direction cosines of a local orthogonal system were obtained. The locus of the local origins represents the folding of the polypeptide. A color-coded origin-origin distance plot similar to that of C alpha-C alpha distance plot was generated. This plot may be used to visually compare and contrast two structures. We identified linear regions in the distribution of the local origins and assigned a secondary structure description. Parameters describing the interrelation between various secondary structure segments were calculated. We have illustrated our crepe-ribbon representation by comparing two phospholipase A2 structures in the Brookhaven National Laboratory Protein Data Bank.

Algorithms↗
PubMed1991

PRENRL_3D: a computer program for an automatic creation of NRL_3D, protein sequence-structure database, from the Protein Data Bank.

Recently, we have developed a sequence-structure database of protein information, NRL_3D, that is extracted from the Protein Data Bank (PDB) of the Brookhaven National Laboratory. NRL_3D provides a vehicle for the retrieval of the three-dimensional coordinates of protein fragments as identified by sequence properties. These data are formulated to allow access by standard sequence analysis programs such as those provided by the Protein Identification Resource (PIR). Because the PDB is updated four times per year, semimanual construction of NRL_3D in coordination with these updates becomes a time-consuming and inefficient task. Hence, we have developed a computer program (PRENRL_3D) in the "C" computer language that automatically extracts NRL_3D from the PDB. Although the program was developed in a VAX/VMS environment, care was taken to ensure its portability to other computer systems. Customized versions of the NRL_3D database can be created from the PDB entry files using various options available in PRENRL_3D, such as selection of entries determined at high resolution and with low R-value. The program has been developed modularly and it contains a number of generalized procedures for manipulating various information in the PDB.

Amino Acid Sequence↗
PubMed1990

Molecular mechanics of the interactions of spermine with DNA: DNA bending as a result of ligand binding.

We used energy minimization of a molecular mechanical force field to evaluate spermine interactions with B-form DNA oligomers with either alternating purine/pyrimidine or homopolymeric sequences. Four different positions for spermine docking--within, along, and bridging the minor groove and bridging the major groove--were assessed for each sequence. Interaction at the major groove of alternating purine/pyrimidine sequences appears to be the most favorable of all models assessed, and are associated with significant bending of DNA. Interactions at the major groove of homopolymers were less favorable than those of heteropolymers and showed little or no bending. Interactions with the minor groove were most favorable for spermine positioned near the base of the groove, and became less favorable as spermine was moved toward the top of the groove. Association along the phosphate backbone alone was the least favorable of the interactions.

Chemical Phenomena↗
PubMed1990

NRL-3D: a sequence-structure database derived from the protein data bank (PDB) and searchable within the PIR environment.

The protein identification resource (PIR) and the Brookhaven National Laboratory protein data bank (PDB) are well-known databases for primary sequences and three-dimensional structures of proteins, respectively. Lesk et al, have compared the primary sequences in these two databases and concluded that the sequences in them are not redundant. Moreover, PIR programs can not be used directly on PDB files to access primary sequences because the FORMATS of these two data bases are different. We have developed a sequence-structure database, called NRL-3D, from the sequences, chain identification and the residue numbers of proteins in the PDB. This new database is designed such that it can be used in conjunction with PIR programs to search and extract sequences of interest and the corresponding three-dimensional coordinates from the structures in PDB.

Amino Acid Sequence↗
PubMed1989

Molecular dynamics of spermine-DNA interactions: sequence specificity and DNA bending for a simple ligand.

We used molecular dynamics to model interactions between the physiologically important polyamine spermine and two B-DNA oligomers, the homopolymer (dG)10-(dC)10 and the heteropolymer (dGdC)5-(dGdC)5. Water and counterions were included in the simulation. Starting coordinates for spermine-DNA complexes were structures obtained by molecular mechanics modeling of spermine with the two oligomers; in these models, spermine binding induced a bend in the heteropolymer but not in the homopolymer. During approximately 40 psec of molecular dynamics simulation, spermine moves away from the floor of the major groove and interacts nospecifically with d(G)10-d(C)10. In contrast, a spermine-induced bend in the helix of (dGdC)5-(dGdC)5 is maintained throughout the simulation and spermine remains closely associated with the major groove. These results provide further evidence that the binding of spermine to nucleic acids can be sequence specific and that bending of alternating purine-pyrimidine sequences may be a physiologically important result of spermine binding.

Base Sequence↗
PubMed1989

Tooth enamel protein, amelogenin, has a probable beta-spiral internal channel, Gln112-Leu138, within a single polypeptide chain: preliminary molecular mechanics and dynamics studies.

Molecular dynamics simulation, with backbone constraints for 20 ps of equilibration and simulation, of a repeating polypeptide segment, Gln-Pro-His-Gln-Pro-Leu-Gln-Pro-His-Gln-Pro-Leu-Gln-Pro-Met-(Gln-Pro-Leu )4, constituting residues 112-138 of bovine amelolgenin, a 19.35 kD hydrophobic protein, are discussed. It is generally believed that the above polypeptide segment is important for the interaction of amelogenin with Ca++ ions, which occurs in the early phases of enamel mineralization. An energetically stable structure of the above polypeptide with recurrent beta-turns is observed and contains a pore of approximately 1 A radius along the helical that can accommodate an unhydrated Ca++ ion. The length of the polypeptide possesses correct dimensions to span a bilayer. The proposed structure is unique among known polypeptide and protein structures.

Amelogenin↗
PubMed1989

Molecular mechanics studies on poly(purine).poly(pyrimidine) sequences in DNA: polymorphism and local variability.

Energy minimization has been carried out on three poly(purine).poly(pyrimidine) sequences--d(G)10.d(C)10, d(A)10.d(T)10, and d(AG)5.d(CT)5--using the molecular mechanics program AMBER (Assisted Model Building and Energy Refinement). In order to extensively scan the conformational space available, five different helical models were studied, three of them being right-handed helices while the other two were left helical. For all three sequences the right-handed A- and B-type helices are energetically slightly preferred over the left helices, but the energy difference between the various right-handed helices is only marginal. A detailed analysis has been carried out to characterize the local structural variability in the refined structures, both in terms of torsion angles as well as other parameters such as base-pair tilt, wedge roll, and wedge tilt, etc. All three sequences exhibit similar structural features for a particular form, but both the forms A and B show significant deviations from fiber models. In particular, the A-form structures have higher unit rise (2.7 A), and lower unit twist (31 degrees) and base-pair tilt (12 degrees), compared to the fiber model, which has corresponding values of 2.56 A, 32.7 degrees, and 20 degrees, respectively. All these changes indicate that the refined models are closer to the A-form structure observed in crystals of oligonucleotides. In the refined B-for models, the helical parameters are close to the fiber B-form, although the torsion angles show considerable variations. None of the three sequences examined, including the d(A)n.d(T)n sequence, show any pronounced curvature for the B-form structure.

Base Sequence↗
PubMed1988

Inter-chain proline:proline contacts contribute to the stability of the triple helical conformation.

The triple helical conformation observed in the collagen group of proteins is related to the presence of large numbers of imino residues and is derived from the stereochemical properties of these residues. The triple helix is stabilized by increasing numbers of these residues. Hydrogen bonds are usually considered to be a major factor in the formation and stability of protein conformation, however, imino residues are not hydrogen bond donors. We have evaluated the role of these residues in stabilizing the triple helix by re-examining two X-ray based structures of the triple helical polypeptide (Pro-Pro-Gly)10 using molecular mechanics calculations. The two minimized structures are comparable in energy and have helical parameters close to the starting values for each starting structure. Our studies suggest that clusters of close van der Waals contacts between proline residues in adjacent chains contribute significantly to the stability of the triple helix. Preliminary NMR studies support this concept. We propose that non-bonded interactions between proline residues may be a significant stabilizing force in the triple helix generated by (Pro-Pro-Gly)10.

Chemical Phenomena↗
PubMed1987

Solution structure of [d(GGTATACC)]2: wrinkled D structure of the TATA moiety.

Phase-sensitive two-dimensional nuclear Overhauser effect spectra of [d(GGTATACC)]2 in aqueous deuterium oxide solution at four mixing times were quantified to give all nonoverlapping cross-peak intensities. A structural model for [d(GGTATACC)]2 was built in which the GG- and -CC moieties were in the B-DNA form, while the middle -TATA- moiety was in the wrinkled-D form (BDB model). This model was subjected to energy refinement by molecular mechanics calculations with the program AMBER. Counterions (Na+) were added to neutralize the charges, and water molecules were placed bridging across the minor groove. A complete relaxation matrix analysis was used to calculate two-dimensional nuclear Overhauser effect spectra of [d(GGTATACC)]2 from the above models (before and after energy refinement) and from four other [d(GGTATACC)]2 structural models: regular A, crystalline A, regular B, and energy-minimized B. Among them, the energy-minimized BDB model yielded a set of theoretical spectra that gave the best fit to the experimental spectra. It was also the energetically most stable. Therefore, it is a good representation of the ensemble- and time-averaged structure of the octamer in solution. This model has backbone torsion angles similar to those of B-form DNA in the GG- and -CC moieties and torsion angles similar to those of wrinkled D form DNA in the -TATA- moiety. The base stacking and base pairing are not interrupted at the junctions between the two structural moieties. Its minor groove is narrower than that of B DNA, and the solvent-accessible surface of the minor groove forms a closed hydration tunnel in the middle -TATA- segment.

Adenine↗
PubMed1987

Modeling and molecular mechanical studies of the cis-thymine glycol radiation damage lesion in DNA.

Computer graphics and energy minimization techniques were used to construct a model of DNA containing cis-thymine glycol, an oxidation product of thymine formed in DNA by ionizing radiation. The model simulated an experimental DNA substrate used to study the effects of this lesion on DNA synthesis in vitro. The results derived from the model indicate that cis-thymine glycol lesions introduce localized perturbations of DNA structure. Specifically the model shows that interactions with the neighboring base pair on the 5' side are significantly destabilized by thymine glycol whereas interactions with the 3' base pair are stabilized by the lesion. The magnitude of these effects is modulated by the nucleotide sequence around the lesion, particularly by the nature of the base on the 3' side. The base pair formed between adenine and thymine glycol is energetically stable and shows minimal distortion, suggesting that this lesion retains the ability to direct the insertion of the correct nucleotide during DNA synthesis.

Base Sequence↗
PubMed1986

Solution structure of [d(A-T)5]2 via complete relaxation matrix analysis of two-dimensional nuclear Overhauser effect spectra and molecular mechanics calculations: evidence for a hydration tunnel.

Pure absorption phase proton two-dimensional nuclear Overhauser effect (2D NOE) spectra at 500 MHz have been obtained for [d(5'ATATATATAT3')]2 in deuterium oxide solution at several mixing times. The 100 nonexchangeable proton resonances have been assigned. The experimental 2D NOE spectra were compared with theoretical spectra calculated by using the complete relaxation matrix analysis method [Keepers, J. W., & James, T. L. (1984) J. Magn. Reson. 57, 404-426] and x-ray diffraction determined molecular coordinates of A, B, alternating B, left-handed B, C, D, and wrinkled D forms of DNA and of energy-minimized structures calculated from the most promising X-ray crystal structures by using the molecular mechanics program AMBER, in which all hydrogens, counterions, and hydration water molecules were included. The analysis of all features of the 2D NOE spectra played an important role in extracting the promising structures, and it was concluded that the wrinkled D form yields the best fit for the 2D NOE data of the A-T decamer. The molecular mechanics calculation indicated that this model structure, whose minor groove is comparatively deep and narrow, may be energetically more stable than the B form for alternating d(A-T) DNA. Interesting features of the structure include possible intra- and interchain sugar-phosphate attractions and a hydration tunnel inside the minor groove capable of accommodating three types of water molecules that aid in helix stabilization via hydrogen bonding. Counterions (sodium) serve to reduce interchain phosphate-phosphate repulsive effects.

Base Sequence↗
PubMed1986

Molecular mechanics studies of dermorphin.

Molecular mechanical simulations have been carried out on dermorphin. Presence of D-Ala2 at the N-terminus and L-Pro6 residue at the C-terminus indicated the probability of beta-turns. From the stereochemical considerations, three types- II', III' and V' - for the beta-turn at the N-terminus of the peptide and two types-I and III- for the C-terminus side of the peptide are possible. In our molecular mechanics calculations, we considered six folded and one extended conformations for dermorphin to asses the relative stabilities. Three of the six folded conformations are lower in energy and have the following general feature-similar in energy, three hydrogen bonds, semirigid beta-sheet segment and favorable Tyr1-Tyr5 interaction. The presence of beta-sheet structure might play a role in mu-receptor selective interaction of dermorphin.

Analgesics, Opioid↗