Archana Pan

Horizontal gene transfer and bacterial diversity

Bacterial genomes are extremely dynamic and mosaic in nature. A substantial amount of genetic information is inserted into or deleted from such genomes through the process of horizontal transfer. Through the introduction of novel physiological traits from distantly related organisms, horizontal gene transfer often causes drastic changes in the ecological and pathogenic character of bacterial species and thereby promotes microbial diversification and speciation. This review discusses how the recent influx of complete chromosomal sequences of various microorganisms has allowed for a quantitative assessment of the scope, rate and impact of horizontally transmitted information on microbial evolution.

Chaos game representation of proteins

The present report proposes a new method for the chaos game representation (CGR) of different families of proteins. Using concatenated amino acid sequences of proteins belonging to a particular family and a 12-sided regular polygon, each vertex of which represents a group of amino acid residues leading to conservative substitutions, the method can generate the CGR of the family and allows pictorial representation of the pattern characterizing the family. An estimation of the percentages of points plotted in different segments of the CGR (grid points) allows quantification of the nonrandomness of the CGR patterns generated. The CGRs of different protein families exhibited distinct visually identifiable patterns. This implies that different functional classes of proteins follow specific statistical biases in the distribution of different mono-, di-, tri-, or higher order peptides along their primary sequences. The potential of grid counts as the discriminative and diagnostic signature of a family of proteins is discussed.

Codon usage in highly expressed genes of Haemophillus influenzae and Mycobacterium tuberculosis: translational selection versus mutational bias

Biases in the codon usage and base compositions at three codon sites in different genes of A+T-rich Gram-negative bacterium Haemophillus influenzae and G+C-rich Gram-positive bacterium Mycobacterium tuberculosis have been examined to address the following questions: (1) whether the synonymous codon usage in organisms having highly skewed base compositions is totally dictated by the mutational bias as reported previously (Sharp, P.M., Devine, K.M., 1989. Codon usage and gene expression level in Dictyostelium discoideum: highly expressed genes do prefer optimal codons. Nucleic Acids Res. 17, 5029-5039), or is also controlled by translational selection; (2) whether preference of G in the first codon positions by highly expressed genes, as reported in Escherichia coli (Gutierrez, G., Marquez, L., Marin, A., 1996. Preference for guanosine at first codon position in highly expressed Escherichia coli genes. A relationship with translational efficiency. Nucleic Acids Res. 24, 2525-2527), is true in other bacteria; and (3) whether the usage of bases in three codon positions is species-specific. Result presented here show that even in organisms with high mutational bias, translational selection plays an important role in dictating the synonymous codon usage, though the set of optimal codons is chosen in accordance with the mutational pressure. The frequencies of G-starting codons are positively correlated to the level of expression of genes, as estimated by their Codon Adaptation Index (CAI) values, in M. tuberculosis as well as in H. influenzae in spite of having an A+T-rich genome. The present study on the codon preferences of two organisms with oppositely skewed base compositions thus suggests that the preference of G-starting codons by highly expressed genes might be a general feature of bacteria, irrespective of their overall G+C contents. The ranges of variations in the frequencies of individual bases at the first and second codon positions of genes of both H. influenzae and M. tuberculosis are similar to those of E. coli, implying that though the composition of all three codon positions is governed by a selection-mutation balance, the mutational pressure has little influence in the choice of bases at the first two codon positions, even in organisms with highly biased base compositions.

Identification and Characterization of Potential Therapeutic Candidates in Emerging Human Pathogen Mycobacterium abscessus: A Novel Hierarchical In Silico Approach

Mycobacterium abscessus, a non-tuberculous rapidly growing mycobacterium, is recognized as an emerging human pathogen causing a variety of infections ranging from skin and soft tissue infections to severe pulmonary infections. Lack of an optimal treatment regimen and emergence of multi-drug resistance in clinical isolates necessitate the development of better/new drugs against this pathogen. The present study aims at identification and qualitative characterization of promising drug targets in M. abscessus using a novel hierarchical in silico approach, encompassing three phases of analyses. In phase I, five sets of proteins were mined through chokepoint, plasmid, pathway, virulence factors, and resistance genes and protein network analysis. These were filtered in phase II, in order to find out promising drug target candidates through subtractive channel of analysis. The analysis resulted in 40 therapeutic candidates which are likely to be essential for the survival of the pathogen and non-homologous to host, human anti-targets, and gut flora. Many of the identified targets were found to be involved in different metabolisms (viz., amino acid, energy, carbohydrate, fatty acid, and nucleotide), xenobiotics degradation, and bacterial pathogenicity. Finally, in phase III, the candidate targets were qualitatively characterized through cellular localization, broad spectrum, interactome, functionality, and druggability analysis. The study explained their subcellular location identifying drug/vaccine targets, possibility of being broad spectrum target candidate, functional association with metabolically interacting proteins, cellular function (if hypothetical), and finally, druggable property. Outcome of the present study could facilitate the identification of novel antibacterial agents for better treatment of M. abscesses infections.

Proteome composition in Plasmodium falciparum: higher usage of GC-rich nonsynonymous codons in highly expressed genes.

The parasite Plasmodium falciparum, responsible for the most deadly form of human malaria, is one of the extremely AT-rich genomes sequenced so far and known to possess many atypical characteristics. Using multivariate statistical approaches, the present study analyzes the amino acid usage pattern in 5038 annotated protein-coding sequences in P. falciparum clone 3D7. The amino acid composition of individual proteins, though dominated by the directional mutational pressure, exhibits wide variation across the proteome. The Asn content, expression level, mean molecular weight, hydropathy, and aromaticity are found to be the major sources of variation in amino acid usage. At all stages of development, frequencies of residues encoded by GC-rich codons such as Gly, Ala, Arg, and Pro increase significantly in the products of the highly expressed genes. Investigation of nucleotide substitution patterns in P. falciparum and other Plasmodium species reveals that the nonsynonymous sites of highly expressed genes are more conserved than those of the lowly expressed ones, though for synonymous sites, the reverse is true. The highly expressed genes are, therefore, expected to be closer to their putative ancestral state in amino acid composition, and a plausible reason for their sequences being GC-rich at nonsynonymous codon positions could be that their ancestral state was less AT-biased. Negative correlation of the expression level of proteins with respective molecular weights supports the notion that P. falciparum, in spite of its intracellular parasitic lifestyle, follows the principle of cost minimization.

A Bioinformatics Resource for TWEAK-Fn14 Signaling Pathway

TNF-related weak inducer of apoptosis (TWEAK) is a new member of the TNF superfamily. It signals through TNFRSF12A, commonly known as Fn14. The TWEAK-Fn14 interaction regulates cellular activities including proliferation, migration, differentiation, apoptosis, angiogenesis, tissue remodeling and inflammation. Although TWEAK has been reported to be associated with autoimmune diseases, cancers, stroke, and kidney-related disorders, the downstream molecular events of TWEAK-Fn14 signaling are yet not available in any signaling pathway repository. In this paper, we manually compiled from the literature, in particular those reported in human systems, the downstream reactions stimulated by TWEAK-Fn14 interactions. Our manual amassment of the TWEAK-Fn14 pathway has resulted in cataloging of 46 proteins involved in various biochemical reactions and TWEAK-Fn14 induced expression of 28 genes. We have enabled the availability of data in various standard exchange formats from NetPath, a repository for signaling pathways. We believe that this composite molecular interaction pathway will enable identification of new signaling components in TWEAK signaling pathway. This in turn may lead to the identification of potential therapeutic targets in TWEAK-associated disorders.

Compositional variation in bacterial genes and proteins with potential expression level

Usage of guanine and cytosine at three codon sites in eubacterial genes vary distinctly with potential expressivity, as predicted by Codon Adaptation Index (CAI). In bacteria with moderate/high GC‐content, G3 follows a biphasic relationship, while C3 increases with CAI. In AT‐rich bacteria, correlation of CAI is negative with G3, but non‐specific with C3. Correlations of CAI with residues encoded by G‐starting codons are positive, while with those by C‐starting codons are usually negative/random. Average Size/Complexity Score and aromaticity of gene‐products decrease with CAI, confirming general validity of cost‐minimization principle in free‐living eubacteria. Alcoholicity of bacterial gene‐products usually decreases with expressivity.

Modeling, docking, simulation, and inhibitory activity of the benzimidazole analogue against β-tubulin protein from Brugia malayi for treating lymphatic filariasis

The nematode Wuchereria bancrofti and Brugia malayi are the causative agents of Lymphatic Filariasis, which is one of the leading causes of permanent and long-term disability in the world. Tubulin protein being involved in many cellular functions is a crucial drug target for nematodes. To have structural insights of this protein, a three dimensional model of B. malayi β-tubulin protein (BmBTP) was built using homology modeling. Docking study was performed on a selected set of ten anti-filarial drugs such as Albendazol, Albendazol sulfoxide, Albendazol sulfone (ABZSOO), Benzimidazole, Carbofuran, Coumaphos, Diethylcarbamazine, Methiazole, Santonin, and Thiabendazole (TBZ) with BmBTP. The docking analysis revealed that Ser-138, Gly-10, and Cys-12 play the most critical role for H-bond interaction, whereas Thr-143, Gly-140, Gly-142, Gly-144, Gln-11, and Ala-9 make extensive van der Waal and hydrophobic contacts. The molecular dynamics (MD) simulation was performed using GROMACS4.0, at 3xa0ns in order to evaluate the overall stability of the BmBTP and anti-filarial drug complexes. The MD’s trajectories depict that the complexes of the BmBTP–ligand are stable throughout the simulation except for TBZ. ABZSOO formed the best and stable complex with BmBTP, whereas remaining ligands were found to be as moderate inhibitors.

Genus specific evolution of codon usage and nucleotide compositional traits of poxviruses

Poxviruses are complex in their nucleotide compositional features of the coding regions. The codon usages in Poxviruses are in accordance with their compositional bias. In the Poxviridae family, codon usage patterns and nucleotide compositional traits are widely divergent across species but some conservation was observed within a genus. Viruses from six Chordopox genera, i.e., Avipoxvirus, Capripoxvirus, Cervidpoxvirus, Orthopoxvirus, Suipoxvirus, Yatapoxvirus, and one Entomopox genus- Betaentomopoxvirus, and some unclassified Entomopoxvirus are significantly rich in AT composition. Four other Chordopox genera- Molluscipoxvirus, Orthopoxvirus, Parapoxvirus, and some unclassified Chordopoxvirus are dominated by the GC rich viruses. Poxviruses from these AT rich and GC rich genera preferred AT or GC ending codons owing to their respective nucleotide compositional bias. For example, viruses from AT rich Orthopoxvirus, or GC rich Parapoxvirus have evolved with mutually exclusive type codon preferences following their genus-specific nucleotide compositions. Additional factors like gene length and expression level also influenced their codon usage patterns to some extent in some Poxvirus genera. Evidences from correspondence analysis and cluster analysis on the extent of divergence in codon usage also support this genus specific evolution of Poxvirus codon usage. Analyzes suggest that most of the Poxviruses from different genera, have evolved in almost two different evolutionary trajectory in context of their nucleotide composition and codon usage.

Comparative analyses of codon and amino acid usage in symbiotic island and core genome in nitrogen-fixing symbiotic bacterium Bradyrhizobium japonicum

Abstract Genes involved in the symbiotic interactions between the nitrogen-fixing endosymbiont Bradyrhizobium japonicum, and its leguminous host are mostly clustered in a symbiotic island (SI), acquired by the bacterium through a process of horizontal transfer. A comparative analysis of the codon and amino acid usage in core and SI genes/proteins of B. japonicum has been carried out in the present study. The mutational bias, translational selection, and gene length are found to be the major sources of variation in synonymous codon usage in the core genome as well as in SI, the strength of translational selection being higher in core genes than in SI. In core proteins, hydrophobicity is the main source of variation in amino acid usage, expressivity and aromaticity being the second and third important sources. But in SI proteins, aromaticity is the chief source of variation, followed by expressivity and hydrophobicity. In SI proteins, both the mean molecular weight and mean aromaticity of individual proteins exhibit significant positive correlation with gene expressivity, which violate the cost-minimization hypothesis. Investigation of nucleotide substitution patterns in B. japonicum and Mesorhizobium loti orthologous genes reveals that both synonymous and non-synonymous sites of highly expressed genes are more conserved than their lowly expressed counterparts and this conservation is more pronounced in the genes present in core genome than in SI.