Glutathione S-transferases (GSTs: EC18.104.22.168) are a superfamily of multifunctional dimeric enzymes that catalyze the conjugation of glutathione (GSH) to electrophilic chemicals. In most animals and in humans, GSTs are the principal enzymes responsible for detoxifying the mycotoxin aflatoxin B1 (AFB1) and GST dysfunction is a known risk factor for susceptibility towards AFB1. Turkeys are one of the most susceptible animals known to AFB1, which is a common contaminant of poultry feeds. The extreme susceptibility of turkeys is associated with hepatic GSTs unable to detoxify the highly reactive and electrophilic metabolite exo-AFB1-8,9-epoxide (AFBO). In this study, comparative genomic approaches were used to amplify and identify the α-class tGST genes (tGSTA1.1, tGSTA1.2, tGSTA1.3, tGSTA2, tGSTA3 and tGSTA4) from turkey liver. The conserved GST domains and four α-class signature motifs in turkey GSTs (with the exception of tGSTA1.1 which lacked one motif) confirm the presence of hepatic α-class GSTs in the turkey. Four signature motifs and conserved residues found in α-class tGSTs are (1) xMExxxWLLAAAGVE, (2) YGKDxKERAxIDMYVxG, (3) PVxEKVLKxHGxxxL and (4) PxIKKFLXPGSxxKPxxx. A BAC clone containing the α-class GST gene cluster was isolated and sequenced. The turkey α-class GTS genes genetically map to chromosome MGA2 with synteny between turkey and human α-class GSTs and flanking genes. This study identifies the α-class tGST gene cluster and genetic markers (SNPs, single nucleotide polymorphisms) that can be used to further examine AFB1 susceptibility and resistance in turkeys. Functional characterization of heterologously expressed proteins from these genes is currently underway.
Bibliographical noteFunding Information:
The authors thank L.D. Chaves for assistance in BAC screening and sequence annotation. We also thank Dr. Lynn Bagley of the Moroni Feed Cooperative for generously providing turkeys and feed for this study. This research was supported in part by NRI competitive grant 2004-35205-14217 from the USDA-CSREES , by competitive grant 2007-35205-17880 from the USDA CSREES , Animal Genome program, and support from the Minnesota, and Utah and Agricultural Experiment Stations, where this is published as paper 8122.
- Aflatoxin B1
- Glutathione S-transferases