Recombinant Spodoptera littoralis nuclear polyhedrosis virus Ecdysteroid UDP-glucosyltransferase (EGT)

Introduction

The Spodoptera littoralis multicapsid nuclear polyhedrosis virus (SlMNPV) is a member of the Baculoviridae family. It exhibits a distant genetic relationship to Autographa californica MNPV (AcMNPV) . SlMNPV contains an ecdysteroid UDP-glucosyltransferase (EGT) gene . EGTs, or UDP-glycosyltransferases (UGTs), are a superfamily of enzymes that play a vital role in the biotransformation of various hydrophobic compounds into more hydrophilic products .

Identification and Sequence

Researchers identified and mapped an egt gene in the genome of SlMNPV using an AcMNPV gene-specific probe . Sequence determination from the hybridizing DNA fragment revealed an open reading frame of 1548 nucleotides . This sequence exhibits 38% and 44% identity to the egt amino acid sequences of AcMNPV and Lymantria dispar MNPV (LdMNPV), respectively . The sequences flanking the SlMNPV egt gene, including the promoter region, are unique to the virus . The presence of this nonstructural gene in SlMNPV and several other baculoviruses points to the importance of egt for the viral infection process .

Function of EGT

UDP-glycosyltransferases (UGTs) facilitate the glycosylation of small lipophilic xenobiotics or endobiotics with sugars such as glucuronic acid, glucose, xylose, N-acetylglucosamine, or galactose . UGTs catalyze the covalent addition of a glycosyl group from uridine diphosphate (UDP) glucose to hydrophobic compounds containing hydroxyl, carboxyl, or amino functional groups through glycosylation . The resulting glycosides are more polar metabolites that can be easily excreted from the cell . Glucose conjugation is involved in physiological processes in insects, including pigmentation, cuticle formation, and metabolic detoxification .

Role in Viral Infection

The egt gene is present in SlMNPV and several other baculoviruses, suggesting its importance for the viral infection process . Nuclear polyhedrosis viruses (NPV) are obligate pathogens . The normal way of infection is by ingestion of polyhedra, but, in some cases, virions can infect host insects . After ingestion, viruses are liberated due to alkaline gut juice, which attacks the nuclei of cell tissue and fat bodies . After 24 to 72 hours of infection, polyhedra can be detected in the nuclei of infected cells .

EGT and Insecticide Resistance

Insects can increase the expression of detoxification enzymes to cope with stress from xenobiotics, including insecticides . UDP-glycosyltransferases (UGTs) are pivotal in insecticide resistance by transforming hydrophobic substrates into more hydrophilic forms for efficient cell elimination .