Abstract
Glutathione S-transferases (GSTs) are enzymes capable of metabolizing cytotoxic compounds. The enzyme AgGSTE2, member of epsilon class GSTs (GSTE), is the most important GST conferring resistance to dichloro-diphenyl-trichloroethane (DDT) in Anopheles gambiae. We have investigated the conformational dynamics of three GSTE variants (GSTE2, GSTE2-I114T/F120L, GSTE5) from A. gambiae. Large-scale motions of helices H2 and H4 and conformational transition of the C-terminal governs the opening of the G-site and is expected to affect substrate binding and product release. This structural rearrangement places Glu116 (Glu120 in GSTE5) close of the thiol group of the tripeptide glutathione (GSH) cofactor, making this residue a candidate to act as a base in the activation of DDT. The structural rearrangement is noticeable for AgGSTE2-F120L, which has been shown to confer increased DDT-resistance. The other variants exhibit a more subtle rearrangement. These findings corroborate the hypothesis that the increase of the conformational dynamics of GST Epsilon class isoforms from A. gambiae promotes higher DDTase activity.
Highlights
Glutathione transferases (EC 2.5.1.18) are highly promiscuous proteins where broad functional promiscuity co-exists with highly conserved structural fold
The DDT molecule binds to AgGSTE2 in a well-defined conformation, which places the β-hydrogen of the ligand within ca. 2 Å of the thiolate group of GSH
This conformation is consistent with an elimination reaction for the conversion of DDT into DDE as proposed from the manual modeling of DDT into the active site of the X-ray structure of AgGSTE2.17 DDT adopts the same conformation upon binding to the AgGSTE2 variants, regardless of the presence of Phe[120] or Leu[120] (Figure 2)
Summary
Glutathione transferases (EC 2.5.1.18) are highly promiscuous proteins where broad functional promiscuity co-exists with highly conserved structural fold. The number of isoforms per class varies widely, ranging from one to forty.[4] A single GST isoform is capable of conjugating glutathione to several hydrophobic substrates. Such promiscuity when coupled with the large number of isozymes generates a large range of potential substrates
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