Ponnusamy Balasubramanian

Purification and characterization of an extracellular α‐glucosidase protein from Trichoderma viride which degrades a phytotoxin associated with sheath blight disease in rice

Aims: To purify and characterize an extracellular α‐glucosidase from Trichoderma viride capable of inactivating a host‐specific phytotoxin, designated RS toxin, produced by the rice sheath blight pathogen, Rhizoctonia solani Kühn.

Computer-Aided Drug Design for Cancer-Causing H-Ras p21 Mutant Protein

GTP-bound mutant form H-Ras (Harvey-Ras) proteins are found in 30% of human tumors. Activation of H-Ras is due to point mutation at positions 12, 13, 59 and/or 61 codon. Mutant form of H-Ras proteins is continuously involved in signal transduction for cell growth and proliferation through interaction of downstream-regulated protein Raf. In this paper, we have reported the virtual screening of lead compounds for H-Ras P 21 mutant protein from ChemBank and DrugBank databases using LigandFit and DrugBank-BLAST. The analysis resulted in 13 hits which were docked and scored to identify structurally active leads that make similar interaction to those of bound complex of H-Ras P 21 mutant- Raf. This approach produced two different leads, 3-Aminopropanesulphonic acid (docked energy -3.014 kcal/mol) and Hydroxyurea (docked energy -0.009 kcal/mol) with finest Lipinskis rule-of-five. Their docked energy scores were better than the complex structure of H-Ras P 21 mutant protein bound with Raf (1.18 kcal/mol). All the leads were docked into ef- fector region forming interaction with ILE36, GLU37, ASP38 and SER39.

Overexpression of thaumatin-like protein in transgenic tomato plants confers enhanced resistance to Alternaria solani

Abstract A cDNA encoding thaumatin-like protein (TLP) from rice was cloned into the binary vector pMON410 under the control of the CaMV 35S promoter for Agrobacterium-mediated transformation of tomato. All putative transformants were tested for the integration and expression of the chimeric gene by polymerase chain reaction (PCR) for hygromycin resistance gene (hph) and enzyme-linked immunosorbent assay (ELISA) for TLP respectively. Constitutive, high-level expression of TLP was observed in transgenic plants. The transgenic lines exhibited increased resistance to Alternaria solani, the early blight pathogen compared to non-transgenic tomato plants.

Functional insight for β-glucuronidase in Escherichia coli and Staphylococcus sp. RLH1

Glycosyl hydrolases hydrolyze the glycosidic bond either in carbohydrates or between carbohydrate and non-carbohydrate moiety. The β-glucuronidase (beta D-glucuronoside glucuronosohydrolase; EC 3.2.1.31) enzyme belongs to the family-2 glycosyl hydrolase. The E. coli borne β-glucuronidase gene (uidA) was devised as a gene fusion marker in plant genetic transformation experiments. Recent plant transformation vectors contain a novel β-glucuronidase (gusA) derived from Staphylococcus sp. RLH1 for E. coli uidA. It is known to have a ten fold higher sensitivity compared to E. coli β-glucuronidase. The functional superiority of Staphylococcus (gusA) over E. coli (uidA) activity is not fully known. The comparison of secondary structural elements among them revealed an increased percentage of random coils in Staphylococcus β-glucuronidase. The 3D model of gusA shows catalytic site residues 396Glu, 508Glu and 471Tyr of gusA in loop regions. Accessible surface area (ASA) calculations on the 3D model showed increased ASA for active site residues in Staphylococcus β-glucuronidase. Increased random coil, the presence of catalytic residues in loops, greater solvent accessibility of active residues and increased charged residues in gusA of Staphylococcus might facilitate interaction with the solvent. This hypothesizes the enhanced catalytic activity of β-glucuronidase in Staphylococcus sp. RLH1 compared to that in E. coli.

β‐glucuronidase of family‐2 glycosyl hydrolase: A missing member in plants

Glycosyl hydrolases hydrolyze the glycosidic bond in carbohydrates or between a carbohydrate and a non‐carbohydrate moiety. β‐glucuronidase (GUS) is classified under two glycosyl hydrolase families (2 and 79) and the family‐2 β‐glucuronidase is reported in a wide range of organisms, but not in plants. The family‐79 endo-β-glucuronidase (heparanase) is reported in microorganisms, vertebrates and plants. The E. coli family‐2 β‐glucuronidase (uidA) had been successfully devised as a reporter gene in plant transformation on the basis that plants do not have homologous GUS activity. On the contrary, histochemical staining with X‐Gluc was reported in wild type (non-transgenic) plants. Data shows that, family‐2 β‐glucuronidase homologous sequence is not found in plants. Further, β‐glucuronidases of family‐2 and 79 lack appreciable sequence similarity. However, the catalytic site residues, glutamic acid and tyrosine of the family‐2 β‐glucuronidase are found to be conserved in family‐79 β‐glucuronidase of plants. This led to propose that the GUS staining reported in wild type plants is largely because of the broad substrate specificity of family‐79 β-glucuronidase on X‐Gluc and not due to the family‐2 β‐glucuronidase, as the latter has been found to be missing in plants.

Differential expression of defense‐related proteins of rice and sheath blight symptoms in response to active and inactive Rhizoctonia solani toxin

The effects of the phyotoxin from the fungal pathogen Rhizoctonia solani, causing sheath blight on the expression of defense‐related proteins of rice were investigated. The toxin inactivated by chemical treatment and by the toxin‐inactivating enzyme α‐glucosidase produced by Trichoderma viride was used in the study along with the active toxin. Toxin inactivated by T. viride α‐glucosidase and sodium periodate caused significantly less damage and electrolyte leakage to test plants. The active toxin and the pathogen induced chitinase and ß‐1,3‐glucanase synthesis in rice plants, while the inactivated toxin did not have any effect on the expression of these pathogenesis‐related proteins. The toxin was found to suppress the peroxidase activity 72 h after inoculation and the inactivated toxin restored the activity as that of untreated plants. There was no remarkable change in phenylalanine ammonia lyase activity in rice sheath treated with both the forms of the toxin.

ExSer: A standalone tool to mine protein data bank (PDB) for secondary structural elements.

Detailed structural analysis of protein necessitates investigation at primary, secondary and tertiary levels, respectively. Insight into protein secondary structures pave way for understanding the type of secondary structural elements involved (α-helices, β-strands etc.), the amino acid sequence that encode the secondary structural elements, number of residues, length and, percentage composition of the respective elements in the protein. Here we present a standalone tool entitled “ExSer” which facilitate an automated extraction of the amino acid sequence that encode for the secondary structural regions of a protein from the protein data bank (PDB) file. Availability ExSer is freely downloadable from http://code.google.com/p/tool-exser/