The crystal structures of glutathione S-transferases isozymes 1-3 and 1-4 from Anopheles dirus species B

Glutathione S-transferases (GSTs) are dimeric proteins that play an importa nt role in cellular detoxification. Four GSTs from the mosquito Anopheles d irus species B (Ad), an important malaria vector in South East Asia, are pr oduced by alternate splicing of a single transcription product and were pre viously shown to have detoxifying activity towards pesticides such as DDT. We have determined the crystal structures for two of these alternatively sp liced proteins, AdGST1-3 (complexed with glutathione) and AdGST1-4 (apo, fo rm), at 1.75 and 2.45 Angstrom resolution, respectively. These GST isozymes show differences from the related GST from the Australian sheep blowfly Lu cilia cuprina; in particular, the presence of a C-terminal helix forming pa rt of the active site, This helix causes the active site of the Anopheles G STs to be enclosed. The glutathione-binding helix alpha2 and flanking resid ues are disordered in the AdGST1-4 (apo) structure. yet ordered in the AdGS T1-3 (GSH-bound) structure. suggesting that insect GSTs operate with an ind uced fit mechanism similar to that found in the plant phi- and human pi-cla ss GSTs. Despite the high overall sequence identities, the active site resi dues of AdGST1-4 and AdGST1-3 have different conformations.