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Glutathione transferase (GST) is a superfamily of ubiquitous enzymes, multigenic in numerous organisms and which generally present homodimeric structures. GSTs are involved in numerous biological functions such as chemical detoxification as well as chemoperception in mammals and insects. GSTs catalyze the conjugation of their cofactor, reduced glutathione (GSH), to xenobiotic electrophilic centers. To achieve this catalytic function, GSTs are comprised of a ligand binding site and a GSH binding site per subunit, which is very specific and highly conserved; the hydrophobic substrate binding site enables the binding of diverse substrates. In this work, we focus our interest in a model organism, the fruit fly Drosophila melanogaster (D. mel), which comprises 42 GST sequences distributed in six classes and composing its GSTome. The goal of this study is to describe the complete structural GSTome of D. mel to determine how changes in the amino acid sequence modify the structural characteristics of GST, particularly in the GSH binding sites and in the dimerization interface. First, we predicted the 3D atomic structures of each GST using the AlphaFold (AF) program and compared them with X-ray crystallography structures, when they exist. We also characterized and compared their global and local folds. Second, we used multiple sequence alignment coupled with AF-predicted structures to characterize the relationship between the conservation of amino acids in the sequence and their structural features. Finally, we applied normal mode analysis to estimate thermal B-factors of all GST structures of D. mel. Particularly, we extracted flexibility profiles of GST and identify key residues and motifs that are systematically involved in the ligand binding/dimerization processes and thus playing a crucial role in the catalytic function. This methodology will be extended to guide the in silico design of synthetic GST with new/optimal catalytic properties for detoxification applications.

This study presents a comprehensive analysis of the dimerization interfaces of fly GSTs through sequence alignment. Our investigation revealed GSTE1 as a particularly intriguing target, providing valuable insights into the variations within Delta and Epsilon GST interfaces. The X-ray structure of GSTE1 was determined, unveiling remarkable thermal stability and a distinctive dimerization interface. Utilizing circular dichroism, we assessed the thermal stability of GSTE1 and other Drosophila GSTs with resolved X-ray structures. The subsequent examination of GST dimer stability correlated with the dimerization interface supported by findings from X-ray structural analysis and thermal stability measurements. Our discussion extends to the broader context of GST dimer interfaces, offering a generalized perspective on their stability. This research enhances our understanding of the structural and thermodynamic aspects of GST dimerization, contributing valuable insights to the field.

Glutathione transferases (GSTs) are a superfamily of enzymes which have in common the ability to catalyze the nucleophilic addition of the thiol group of reduced glutathione (GSH) onto electrophilic and hydrophobic substrates. This conjugation reaction, which occurs spontaneously but is dramatically accelerated by the enzyme, protects cells against damages caused by harmful molecules. With some exceptions, GSTs are catalytically active as homodimers, with monomers generally constituted of 200 to 250 residues organized into two subdomains. The first is the N-terminal subdomain, which contains an active site named G site, where GSH is hosted in catalytic conformation and which is generally highly conserved among GSTs. The second subdomain, hydrophobic, which binds the substrate counterpart (H site), can vary from one GST to another, resulting in structures able to recognize different substrates. In the present work, we performed all-atom molecular dynamics simulations in explicit solvent of human GSTA1 in its APO form, bound to GSH ligand and bound to GS-conjugated ligand. From MD, two probes were analyzed to (i) decipher the local conformational changes induced by the presence of the ligand and (ii) map the communication pathways involved in the ligand-binding process. These two local probes are, first, coarse-grained angles (θ,γ), representing the local conformation of the protein main chain and, second, dihedral angles χ representing the local conformation of the amino-acid side chains. From the local probes time series, effective free-energy landscapes along the amino-acid sequence were analyzed and compared between the three different forms of GSTA1. This methodology allowed us to extract a network of 33 key residues, some of them being located in the experimentally well-known binding sites G and H of GSTA1 and others being located as far as 30Å from the original binding sites. Finally, the collective motions associated with the network of key residues were established, showing a strong dynamical coupling between residues Gly14-Arg15 and Gln54-Val55, both in the same binding site (intrasite) but also between binding sites of each monomer (intersites).