Marimuthu Jeya

Cloning and expression of GH11 xylanase gene from Aspergillus fumigatus MKU1 in Pichia pastoris.

A xylanase gene, xynf11a of Aspergillus fumigatus MKU1 was cloned and expressed in Pichia pastoris X33. Two exons of the xynf11a gene were amplified separately and fused by overlap extension PCR. The fused product was cloned in yeast expression vector pPICZB and expressed in P. pastoris under the control of the AOX1 promoter. P. pastoris transformants expressing recombinant xylanases were selected on xylan agar plate and their ability to produce the xylanase was evaluated in flask cultures. P. pastoris X33 (pZBxynf11aFP) efficiently secreted the recombinant xylanase into the medium and produced the high level of xylanase activity (14 U/ml) after 96 h of growth. The recombinant xylanase produced by P. pastoris showed maximum activity at pH 6.0 and temperature 60 degrees C. The recombinant xylanase did not exhibit any cellulase activity and hence it could be potentially used for pretreatment of paper pulp before bleaching.

Probing the Molecular Determinant for the Catalytic Efficiency of l-Arabinose Isomerase from Bacillus licheniformis

ABSTRACT Bacillus licheniformis l-arabinose isomerase (l-AI) is distinguished from other l-AIs by its high degree of substrate specificity for l-arabinose and its high turnover rate. A systematic strategy that included a sequence alignment-based first screening of residues and a homology model-based second screening, followed by site-directed mutagenesis to alter individual screened residues, was used to study the molecular determinants for the catalytic efficiency of B. licheniformisl-AI. One conserved amino acid, Y333, in the substrate binding pocket of the wild-type B. licheniformisl-AI was identified as an important residue affecting the catalytic efficiency of B. licheniformisl-AI. Further insights into the function of residue Y333 were obtained by replacing it with other aromatic, nonpolar hydrophobic amino acids or polar amino acids. Replacing Y333 with the aromatic amino acid Phe did not alter catalytic efficiency toward l-arabinose. In contrast, the activities of mutants containing a hydrophobic amino acid (Ala, Val, or Leu) at position 333 decreased as the size of the hydrophobic side chain of the amino acid decreased. However, mutants containing hydrophilic and charged amino acids, such as Asp, Glu, and Lys, showed almost no activity with l-arabinose. These data and a molecular dynamics simulation suggest that Y333 is involved in the catalytic efficiency of B. licheniformisl-AI.

Glycopeptide Antibiotics and their Novel Semi-Synthetic Derivatives

Glycopeptide antibiotics, vancomycin and teicoplanin, inhibit cell wall synthesis in Gram-positive bacteria by interacting with peptidoglycan D-Ala-D-Ala peptide stem termini of the pentapeptide side chains of the peptidoglycan precursors. In glycopeptide-resistant bacteria, multiresistance poses major therapeutic problems. New potent antibacterial agents are needed to combat these resistance problems, resulting in the explosion of novel glycopeptides in recent years. The glycosylation patterns of glycopeptides and the chemical modifications of the glycosyl moieties greatly influence their antibiotic activity, and certain combinations have resulted in highly active new compounds. Considerable efforts have been made to produce semisynthetic glycopeptides with improved pharmacokinetic and pharmacodynamic properties and activity towards resistant strains. This review provides an overview of the chemistry, the antimicrobial activity, the pharmacokinetics and the toxicology of teicoplanin and other glycopeptide antibiotic derivatives.

Improvement of xylanase production in solid-state fermentation by alkali tolerant Aspergillus versicolor MKU3

Aims:  To optimize the media components for xylanase production by Aspergillus versicolor MKU3 in solid‐state fermentation (SSF).