G Raja Venkatesh

International Centre for Genetic Engineering and Biotechnology, Trst, Friuli Venezia Giulia, India

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Publications (2)6.87 Total impact

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    ABSTRACT: Aminopeptidase-N (APN) and cadherin proteins located at the midgut epithelium of Helicoverpa armigera have been implicated as receptors for the Cry1A subfamily of insecticidal proteins of Bacillus thuringiensis. Ligand blot analysis with heterologously expressed and purified H. armigera Bt receptor with three closely related Cry1A proteins tentatively identified HaAPN1 as an interacting ligand. However, to date there is no direct evidence of APN being a functional receptor to Cry1Ac in H. armigera. Sf21 insect cells expressing HaAPN1 displayed aberrant cell morphology upon overlaying with Cry1Ac protein. Down-regulating expression of HaAPN1 by RNA interference using double-stranded RNA correlated with a corresponding reduction in the sensitivity of HaAPN1-expressing cells to Cry1Ac protein. This clearly establishes that insect cells expressing the receptor recruit sensitivity to the insecticidal protein Cry1Ac, and their susceptibility is directly dependent on the amount of HaAPN1 protein expressed. Most importantly, silencing of HaAPN1 in H. armigera in vivo by RNA interference resulted in reduced transcript levels and a corresponding decrease in the susceptibility of larvae to Cry1Ac. BIAcore analysis of HaAPN1/Cry1Ac interaction further established HaAPN1 as a ligand for Cry1Ac. This is the first functional demonstration of insect aminopeptidase-N of H. armigera being a receptor of Cry1Ac protein of B. thuringiensis.
    No preview · Article · Apr 2007 · Journal of Biological Chemistry
  • R Rajagopal · K Thamilarasi · G Raja Venkatesh · P Srinivas · Raj K Bhatnagar
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    ABSTRACT: Haemolymph associated phenol oxidase is a critical component of invertebrate immune reaction and cuticle sclerotization. Phenol oxidase catalyses the conversion of mono-phenols to diphenols and quinones which finally leads to melanin formation. We have cloned the c-DNA encoding phenol oxidase from the haemocytes of Spodoptera litura and expressed it in Escherichia coli. The encoding gene is 2452bp with an open reading frame of 2091 bp translating into a 697 amino acid protein. Multiple alignment analysis of the predicted protein sequence shows close homology to other lepidopeteran PPOII type genes. The transcription of the gene is induced upon microbial challenge of 6th instar larvae with E. coli and is unresponsive to injury. Cloning of the ORF of SLPPO in-frame in the E. coli expression vector pQE30 resulted in its expression. Enzymatic analysis of the recombinant protein reveals that the recombinant protein is catalytically active on 4-methyl pyrocatechol upon activation by cetyl pyridinium chloride.
    No preview · Article · Dec 2005 · Biochemical and Biophysical Research Communications