News

New publication in Dyes and Pigments!

Very happy to share our new article entitled "Electronic coupling in the reduced state lies at the origin of color changes of ommochromes", which is now availabe in the journal Dyes and Pigments! You can access the published version for free here (link available for 50 days) and the preprint here.

This interdisciplinary study tackles the molecular mechanisms that allow ommochrome pigments to change their color from yellow to red (i.e. bathochromy) upon reduction. Such bathochromic color changes are unusual for animal pigments since chemical reduction is usually associated to color losses (i.e. hypsochromy) due to double bond saturation. Yet, bathochromy is a biologically important phenomenon since some male dragonflies signal their sexual maturity through such color changes. To rationalize and to predict color changes of ommochromes, we used quantum computational methods, namely Density Functional Theory (DFT) and its Time-Dependent version (TDDFT), on ommochrome-like pigments showing either bathochromic or hypsochromic behaviors upon reduction. We found that color changes are solely driven by reduced states, whose capacity to let excited electrons flow is dependent on specific chemical groups. Specifically, because reduced ommochromes possess Electron-Withdrawing Auxochromes (EWA) attached to their phenoxazine core, they absorb light more easily than their oxidized form; hence their batochromic color changes. Those results also point toward a possible better antiradical/antioxidant function for ommochromes since EWA are associated to higher electron affinity. Therefore, besides visual display, color changes in animals might help preventing oxidative stress in some contexts.

This work was performed both at the Insect Biology Research Institute (IRBI, UMR 7261, CNRS - University of Tours) and in the Chemical Theory and Modelling group (CTM, Chimie ParisTech, PSL University, CNRS, Institute of Chemistry for Life and Health Sciences). 

Citation
Figon, F., Casas, J., Ciofini, I. & Adamo, C. (2021). Electronic coupling in the reduced state lies at the origin of color changes of ommochromes. Dyes and Pigments. 185, 108661. DOI: 10.1016/j.dyepig.2020.108661

New publication in Insect Biochemistry and Molecular Biology!

Glad to share our latest article entitled "Uncyclized xanthommatin is a key ommochrome intermediate in invertebrate coloration" published in Insect Biochemistry and Molecular Biology! You can access the published version for free here (link available for 50 days) and the preprint here.

Ommochromes are widespread pigments of invertebrates, whose structure lies at the heart of their functions. Unravelling the biosynthetic pathway that leads to their production within specialized membrane-bound organelles, called ommochromasomes, is of special interest to understand their biological and technological uses. In this study, we identified a key biosynthetic intermediate, uncyclized xanthommatin, in the formation of ommochromes within ommochromasomes of houseflies. This intermediate of the tryptophan-to-ommochrome pathway has remained elusive for nearly 60 years, but using a combination of highly sensitive spectroscopic techniques, we could identify it and assign its unique chemical structure. Our finding provides insights into the structural diversification of ommochromes across invertebrates, from insects to cephalopods.

This work was performed at the Insect Biology Research Institute (IRBI, UMR 7261, CNRS - université de Tours) in close collaboration with the Biomolecule and Plant Biotechnology lab (BBV, EA 2106, université de Tours) and the Genetics, Immunotherapy, Chemistry and Cancer unit (GICC, UMR 7292, CNRS - université de Tours).

Citation
Figon, F., Munsch, T., Croix, C., Viaud-Massuard, M.-C., Lanoue, A., and Casas, J. (2020) Uncyclized xanthommatin is a key ommochrome intermediate in invertebrate coloration. Insect Biochemistry and Molecular Biology. 124, 103403. DOI: 10.1016/j.ibmb.2020.103403