PARCOURS

1992 : Ph.D., Enzymology, University of Aix-Marseille 2 France

1992 : Thierry Michon was awarded the PhD in enzymology at the University of Aix-Marseille 2 France.
In 1993, he accepted a position of researcher at the "Institut de la Recherche Agronomique" in Nantes where he worked on peroxidases catalysis in heterogeneous media.
Between 1998 and 2001 he was appointed by the California Institute of Technology as an invited scientist and worked in close collaboration with Pr. D. Tirrell (Chemical Engineering Dep’t). During this period he contributed to the development of protein based bio inspired materials.
Since 2001 T. Michon has been project leader at the French Institute of Agronomic research (INRA) in Bordeaux France. He studies possible correlations between virus evolution and the intrinsic disorder found in viral proteins. In parallel his team develops virus based Enzymes NanCarriers (ENCs) for nanotechnology applications.

CV en ligne sur le Portail HAL : https://cv.hal.science/thierry-michon

RESEARCH TOPICS

Molecular evolution of virus proteins; virus-inspired nanotechnology

Molecular evolution of intrinsic disorder in viral proteins.

Fischer’s lock-and-key model, 100 years ago, opened up the concept of structure-function relationship whereby the folding of a polypeptide chain into an ordered 3D structure conditions the specificity of its function.

However, many biologically functional proteins possess Intrinsically Disordered Regions (IDRs). IDRs are regions devoid of stable secondary and tertiary structures under physiological conditions and rather exist as dynamic ensembles of inter-converting conformers. This lack of a stable 3D structure in many cases is relieved only when the protein binds to its target molecule. The ability to exert specific biological functions and to interact with various partners in spite of the lack of a precise 3D scaffold, challenges the classic paradigm according to which specificity in interacting domains can only be achieved through precise surface complementation between structured and conserved domains. The genome of RNA viruses codes for proteins containing an important proportion of IDRs. Within viral proteins, IDRs often contain binding domains for protein-protein interactions that are crucial to the virus replication cycle. Because of the low steric constraints within IDDs, IDDs are expected to be more tolerant to mutations than structured proteins and thus have the potential to evolve faster. Our objective aims at assessing experimentally if ID in viral proteins favors an exploration of a broader sequence space without serious functional consequences, which could afford a faster adaptation to various hosts. It will in turn be examined whether there is a selective pressure for the conservation of intrinsic disorder (ID) in domains of viral proteins interacting with host factors. Potato virus Y (PVY), a phytovirus within the genus Potyvirus, provides an excellent model system. Indeed, it has been demonstrated that pepper infection by PVY requires the interaction between eIF4E, a factor involved in the host translational machinery, and an IDR within the Virus Protein linked to the genome (VPg). In addition, this IDR contains several amino acid positions that are subject to positive selection, i.e. presumably involved in virus adaptation. We also experimentally explore whether a correlation exists between ID and mutational robustness (relaxed constraint) or adaptive evolution (positive selection) from one hand (Figure 1) and between the structural flexibility in the VPgs IDRs and a faster adaptability to the host on the other hand. Our analysis combine, in silico, in vitro and in vivo studies using complementary skills through bioinformatics, biological, biochemical and biophysical approaches [1-8]. We performed an in silico analysis of the content in ID of the Potyvirus proteome both at inter- and intra-species scales. This work unveiled a high content in ID, which is conserved during Potyvirus evolution, suggesting a functional advantage of IDRs [9]. In collaboration with the Benoit Moury team (INRA, Avignon), we obtained the first in vivo experimental data supporting the hypothesis that ID could directly modulate virus adaptability to the host, possibly by enabling a faster exploration of the mutational space thereby allowing the virus to bypass the plant resistance. These original data, which strongly suggest that IDRs contribute to adaptive mechanisms of plant viruses, were published in a landmark paper [10]. These results offer an appropriate starting point to explore more systematically correlations between adaptation and ID. We recently published a kinetic analysis allowing to specify the contribution of the VPg central helix and its appended disordered region to VPg association with eIF4E [11].

A controlled positioning of enzymes on virus nano-scaffolds.

A

B - C

D

Functional imaging of single biomolecules at work (and especially enzymes) has become the Grail of scientists and technologists. It will not only help to understand in real time molecular mechanisms, for instance enzyme cascades, at the molecular level but will also have high impact for the design of nano-transducers and lab-on-a-chip applications. However, there are very few methods available to systematically evaluate how spatial factors (e.g., position, orientation) influence enzymatic activity. This limitation notably comes from the fact that their small size makes it extremely difficult to organize biomolecules onto surfaces in order to form fully active supramolecular complexes amenable to experimental studies. We have developped a strategy to spatially organize enzymes on a solid substrate making use of robust Virus NanoCarriers (VNC’s) as positioning helpers (Figure 2A). Viruses are attractive building blocks for a large panel of biotechnology applications such as enzyme chips, protein selection, molecular therapy, or to study more fundamental problems raised by modern enzymology Viruses are here highly interesting as natural nano-carriers since their ordered protein backbones afford a high degree of positional control of functional molecules which can be attached selectively to their surface. These VNCs are then used as intermediate building blocks or scaffolds carrying correctly exposed proteins on their surface, and subsequently immobilized onto a solid substrate. Filamentous viruses such as the potyvirus PVA (700 nm long, 14 nm diameter), or M13 Bacteriophage (800 nm, 8 nm diameter), a virus that has shown its potential for biotechnological applications are our work-horse systems. Knowing the structure of these viruses, genetic engineering can be used to optimize the desired enzyme's topology on the virus nanocarrier [12-13]. In the frame of a strong collaboration between the laboratory of molecular electro-chemistry (CNRS-Univ. Paris ) and our team, high resolution imaging of virus particles were obtained by AFM-SECM (figure 2B). We used this technology to bridge the gap between our two main research themes. We imaged eIF4E, a plant translation factor interacting specifically to the viral protein VPg exposed at the surface of a potyvirus nanoparticle, figure 2C [17]. Our experimental setup allows a precise kinetic analysis of a small population of enzymes (100-200 individuals) adsorbed on single viral particles [18]. We recently imaged catalytic electron fluxes at the surface of functionalized virus particles, figure 2D [19].

PUBLICATIONS

Liste complète des publications sur le portail HAL-INRAE

FURTHER INFORMATIONS

The team

June 2012

April 2015