Articles written in Journal of Biosciences

    • Is hexamerin receptor a GPI-anchored protein in Achaea janata (Lepidoptera: Noctuidae)?

      Madhusudhan Budatha Thuirei Jacob Ningshen Aparna Dutta-Gupta

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      The process of uptake of hexamerins during metamorphosis from insect haemolymph by fat body cells is reminiscent of receptor-mediated endocytosis. Previously, we had identified a hexamerin-binding protein (HBP) and reported for the first time that uptake of hexamerins is dependent on the phosphorylation of HBP partly by a tyrosine kinase, which is, in turn, activated by 20-hydroxyecdysone (20E). However, the exact nature of HBP and the mechanism of interaction are still unknown. Here we report the possibility of HBP being a GPI-anchored protein in the fat body of Achaea janata and its role in the tyrosine-kinase-mediated phosphorylation signalling. Digestion of fat body membrane preparation with bacterial phosphatidylinositol-specific phospholipase C (PI-PLC), and the subsequent recognition by antibodies specific for the cross-reacting determinant (CRD), revealed that HBP is glycosylphosphatidylinositol (GPI)-anchored protein and, further, that the hexamerin binding to HBP was inhibited after digestion. Hexamerin overlay assay (HOA) of co-immunoprecipitated in vitro phosphorylated HBP showed exclusive binding to ∼120 kDa protein. Lectin-binding analysis of hexamerins revealed the presence of 𝑁-acetylgalactosamine (GalNAc) and 𝑁-acetylglucosamine (GluNAc), whereas HBP showed the presence of GalNac alone. Mild chemical deglycosylation studies and binding interaction in the presence of sugars revealed that glycan moieties are possibly not involved in the interaction between HBP and hexamerins. Taken together, these results suggest that HBP may be a GPI-anchored protein, and interaction and activation of HBP is through lipid-linked non-receptor src tyrosine kinases. However, additional studies are needed to prove that HBP is a GPI-anchored protein.

    • Midgut aminopeptidase N expression profile in castor semilooper (Achaea janata) during sublethal Cry toxin exposure


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      The midgut of lepidopteran larvae is a multifunctional tissue that performs roles in digestion, absorption,immunity, transmission of pathogens and interaction with ingested various molecules. The proteins localized atthe inner apical brush border membrane are primarily digestive proteases, but some of them, likeaminopeptidase N, alkaline phosphatase, cadherins, ABC transporter C2, etc., interact with Crystal (Cry) toxinsproduced by Bacillus thuringiensis (Bt). In the present study, aminopeptidase N (APN) was characterized asCry-toxin-interacting protein in the larval midgut of castor semilooper, Achaea janata. Transcriptomic andproteomic analyses revealed the presence of multiple isoforms of APNs (APN1, 2, 4, 6 and 9) which have lessthan 40% sequence similarity but show the presence of characteristic ‘GAMENEG’ and zinc-binding motifs.Feeding a sublethal dose of Cry toxin caused differential expression of various APN isoform. Further, 6thgenerationCry-toxin-exposed larvae showed reduced expression of APN2. This report suggests that A. janatalarvae exploit altered expression of APNs to overcome the deleterious effects of Cry toxicity, which mightfacilitate toxin tolerance in the long run.

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