K. Sekar

3dSS: 3D structural superposition

3dSS is a web-based interactive computing server, primarily designed to aid researchers, to superpose two or several 3D protein structures. In addition, the server can be effectively used to find the invariant and common water molecules present in the superposed homologous protein structures. The molecular visualization tool RASMOL is interfaced with the server to visualize the superposed 3D structures with the water molecules (invariant or common) in the client machine. Furthermore, an option is provided to save the superposed 3D atomic coordinates in the client machine. To perform the above, users need to enter Protein Data Bank (PDB)-id(s) or upload the atomic coordinates in PDB format. This server uses a locally maintained PDB anonymous FTP server that is being updated weekly. This program can be accessed through our Bioinformatics web server at the URL or .

Structure of Mycobacterium tuberculosis single-stranded DNA-binding protein. Variability in quaternary structure and its implications

Single-stranded DNA-binding protein (SSB) is an essential protein necessary for the functioning of the DNA replication, repair and recombination machineries. Here we report the structure of the DNA-binding domain of Mycobacterium tuberculosis SSB (MtuSSB) in four different crystals distributed in two forms. The structure of one of the forms was solved by a combination of isomorphous replacement and anomalous scattering. This structure was used to determine the structure of the other form by molecular replacement. The polypeptide chain in the structure exhibits the oligonucleotide binding fold. The globular core of the molecule in different subunits in the two forms and those in Escherichia coli SSB (EcoSSB) and human mitochondrial SSB (HMtSSB) have similar structure, although the three loops exhibit considerable structural variation. However, the tetrameric MtuSSB has an as yet unobserved quaternary association. This quaternary structure with a unique dimeric interface lends the oligomeric protein greater stability, which may be of significance to the functioning of the protein under conditions of stress. Also, as a result of the variation in the quaternary structure the path adopted by the DNA to wrap around MtuSSB is expected to be different from that of EcoSSB.

A FAST pattern matching algorithm.

The advent of digital computers has made the routine use of pattern-matching possible in various applications. This has also stimulated the development of many algorithms. In this paper, we propose a new algorithm that offers improved performance compared to those reported in the literature so far. The new algorithm has been evolved after analyzing the well-known algorithms such as Boyer-Moore, Quick-search, Raita, and Horspool. The overall performance of the proposed algorithm has been improved using the shift provided by the Quick-search bad-character and by defining a fixed order of comparison. These result in the reduction of the character comparison effort at each attempt. The best- and the worst- case time complexities are also presented in this paper. Most importantly, the proposed method has been compared with the other widely used algorithms. It is interesting to note that the new algorithm works consistently better for any alphabet size.

Structural biology of Mycobacterium tuberculosis proteins: The Indian efforts

Among the many different objectives of large scale structural genomics projects are expanding the protein fold space, enhancing understanding of a model or disease-related organism, and providing foundations for structure-based drug discovery. Systematic analysis of protein structures of Mycobacterium tuberculosis has been ongoing towards meeting some of these objectives. Indian participation in these efforts has been enthusiastic and substantial. The proteins of M.xa0tuberculosis chosen for structural analysis by the Indian groups span almost all the functional categories. The structures determined by the Indian groups have led to significant improvement in the biochemical knowledge on these proteins and consequently have started providing useful insights into the biology of M.xa0tuberculosis. Moreover, these structures form starting points for inhibitor design studies, early results of which are encouraging. The progress made by Indian structural biologists in determining structures of M.xa0tuberculosis proteins is highlighted in this review.

Brief communication: ProSTRIP: A method to find similar structural repeats in three-dimensional protein structures

The occurrence of similar structural repeats in a protein structure has evolved through gene duplication. These repeats act as a structural building block and form more than one compact structural and functional unit called a repeat domain. The protein families comprising similar structural repeats are mainly involved in protein-protein interactions as well as binding to other ligand molecules. The identification of internal sequence repeats in the primary structure is not sufficient for the analysis of structural repeats. Thus, a new method called ProSTRIP has been developed using dynamic programming to find the similar structural repeats in a three-dimensional protein structure. The detection of these repeats is made by calculating the protein backbone Calpha angles. An internet computing server is also created by implementing this method and enables graphical visualization of the results. It can be freely accessed at http://cluster.physics.iisc.ernet.in/prostrip/.

CADB: Conformation Angles DataBase of proteins

Conformation Angles DataBase (CADB) provides an online resource to access data on conformation angles (both main-chain and side-chain) of protein structures in two data sets corresponding to 25% and 90% sequence identity between any two proteins, available in the Protein Data Bank. In addition, the database contains the necessary crystallographic parameters. The package has several flexible options and display facilities to visualize the main-chain and side-chain conformation angles for a particular amino acid residue. The package can also be used to study the interrelationship between the main-chain and side-chain conformation angles. A web based JAVA graphics interface has been deployed to display the user interested information on the client machine. The database is being updated at regular intervals and can be accessed over the World Wide Web interface at the following URL: http://144.16.71.148/cadb/.

Fragment Finder: a web-based software to identify similar three-dimensional structural motif

FF (Fragment Finder) is a web-based interactive search engine developed to retrieve the user-desired similar 3D structural fragments from the selected subset of 25 or 90% non-homologous protein chains. The search is based on the comparison of the main chain backbone conformational angles (phi and ). Additionally, the queried motifs can be superimposed to find out how similar the structural fragments are, so that the information can be effectively used in molecular modeling. The engine has facilities to view the resultant superposed or individual 3D structure(s) on the client machine. The proposed web server is made freely accessible at the following URL: http://cluster.physics.iisc.ernet.in/ff/ or http://144.16.71.148/ff/.

THGS: a web‐based database of Transmembrane Helices in Genome Sequences

Transmembrane Helices in Genome Sequences (THGS) is an interactive web-based database, developed to search the transmembrane helices in the user-interested gene sequences available in the Genome Database (GDB). The proposed database has provision to search sequence motifs in transmembrane and globular proteins. In addition, the motif can be searched in the other sequence databases (Swiss-Prot and PIR) or in the macromolecular structure database, Protein Data Bank (PDB). Further, the 3D structure of the corresponding queried motif, if it is available in the solved protein structures deposited in the Protein Data Bank, can also be visualized using the widely used graphics package RASMOL. All the sequence databases used in the present work are updated frequently and hence the results produced are up to date. The database THGS is freely available via the world wide web and can be accessed at http:// pranag.physics.iisc.ernet.in/thgs/ or http://144.16. 71.10/thgs/.

Observation of Additional Calcium Ion in the Crystal Structure of the Triple Mutant K56,120,121M of Bovine Pancreatic Phospholipase A2

Phospholipase A(2) catalyses hydrolysis of the ester bond at the C2 position of 3-sn-phosphoglycerides. Here we report the 1.9A resolution crystal structure of the triple mutant K56,120,121M of bovine pancreatic phospholipase A(2). The structure was solved by molecular replacement method using the orthorhombic form of the recombinant phospholipase A(2). The final protein model contains all the 123 amino acid residues, two calcium ions, 125 water molecules and one 2-methyl-2-4-pentanediol molecule. The model has been refined to a crystallographic R-factor of 19.6% (R(free) of 25.9%) for all data between 14.2A and 1.9A. The residues 62-66, which are in a surface loop, are always disordered in the structures of bovine pancreatic phospholipase A(2) and its mutants. It is interesting to note that the residues 62-66 in the present structure is ordered and the conformation varies substantially from those in the previously published structures of this enzyme. An unexpected and interesting observation in the present structure is that, in addition to the functionally important calcium ion in the active site, one more calcium ion is found near the N terminus. Detailed structural analyses suggest that binding of the second calcium ion could be responsible for the conformational change and the ordering of the surface loop. Furthermore, the results suggest a structural reciprocity between the k(cat)(*) allosteric site and surface loop at the i-face, which represents a newly identified structural property of secreted phospholipase A(2).

A redetermination of the structure of the triple mutant (K53,56,120M) of phospholipase A2 at 1.6 Å resolution using sulfur-SAS at 1.54 Å wavelength

The crystal structure of the triple mutant K53,56,120M of bovine pancreatic phospholipase A(2) has been redetermined using sulfur single-wavelength anomalous scattering. The synchrotron data were collected at lambda = 1.54 A and the crystal diffracted to 1.6 A resolution. The program SOLVE was used to locate the heavy atoms and to estimate the initial phases and the resulting map was then subjected to RESOLVE. The output of 455 non-H atoms, including 12 S atoms, one calcium ion and one chloride ion, were then subjected to ARP/wARP followed by REFMAC. With the improved phases, the automatic model building successfully built more than 85% of the 123 residues, excluding the N- and C-terminal residues. The final crystallographic R factor is 17.7% (R(free) = 21.7%). The refined model consists of 954 non-H protein atoms, 165 water O atoms, three 2-methyl-2,4-pentanediol (MPD) molecules, one calcium ion and one chloride ion. The present work is yet another example that shows the utility of single-wavelength anomalous scattering data for solving a protein structure.