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abstracts
Inosine-5'-monophosphate dehydrogenase (1, 2) (IMPDH) is a major target for antiviral, antiparasitic, antileukemic and immunosuppressive therapies. It is an ubiquitous and essential enzyme for the biosynthesis of guanosine nucleotides. Up to now, IMPDHs have been reported as tetrameric enzymes harbouring a catalytic domain and a tandem of cystathionine-ß-synthase (CBS) modules. The latter had no precise function assigned despite their nearly absolute conservation among IMPDHs and consistent indication of their importance in vivo. The aim of our study was to provide evidence for the role of the CBS modules on the quaternary structure and on the regulation of IMPDHs. A multidisciplinary approach involving enzymology, site-directed mutagenesis, analytical ultracentrifugation, X-ray crystallography, SAXS, cryo-electron microscopy and molecular modelling allowed us to demonstrate that the Pseudomonas aeruginosa IMPDH is functionally active as an octamer and allosterically regulated by MgATP via each CBS module. Revisiting deposited structural data, we found this newly discovered octameric organization conserved in other IMPDH structures. Meanwhile, we demonstrated that the human IMPDH1 formed two distinct octamers that can pile up into isolated fibres in the presence of MgATP while its pathogenic mutant D226N, localised into the CBS domains, appeared to form massively aggregating fibres. The dramatic impact of this mutation could explain the severe retinopathy adRP10. Our data (3) revealed for the first time that IMPDH has an octameric architecture modulated by MgATP binding to the CBS modules, inducing large structural rearrangements. Thus, the regulatory CBS modules in IMPDHs are functional and they can either modulate catalysis or/and macromolecular assembly. Targeting the conserved effector binding pockets identified within the CBS modules might be promising to develop antibacterial compounds or drugs to counter retinopathy onset.
abstracts
Endocrine-disrupting chemicals (EDCs) are exogenous substances that interfere with the function of hormonal systems and cause deleterious effects on humans and wildlife. Many EDCs are man-made chemicals produced by industry and released into the environment. Some naturally occurring EDCs can also be found in plants or fungi. Epidemiological studies suggest a link between the exposure to these chemicals and the development of diseases like cancers, reproduction defects, or metabolic disorders. Endocrine disruption has raised considerable concern in recent years so that several countries have developed risk assessment programs aimed at evaluating the toxic potential of more than 100,000 chemicals. In this context, we have been using a battery of structural, biophysical and cell-based approaches to investigate the mechanisms by which a variety of environmental pollutants, including bisphenols [1], pesticides, phthalates, benzophenones, parabens, myco- and phytoestrogens or alkylphenols, bind to and modulate the activity of the estrogen receptors ERα and ERβ, two nuclear hormone receptors (NRs) that are primary targets of environmental contaminants. Crystallographic analysis reveals that these structurally and chemically diverse compounds bind to ERs via diverse sets of protein–ligand interactions reflecting their differential activities, binding affinities and specificities. A detailed analysis of the various binding/activation mechanisms will be presented. Based on these structural data, we are developing a protocol for in silico evaluation of the interaction between pollutants and ERs or other members of the NR family. The server which utilises crystal structures to model any NR/xenobiotics complexes and estimate binding affinities will also be presented. Overall, this study provides a wealth of tools and information that could be used for the development of safer chemicals devoid of NR-mediated activity and more generally for environmental risk assessment.
