PhD defense - Jeanne Kergomard

Enzymatic activity on plant lipids: combination of interfacial measurements at the molecular scale (nm) and kinetic measurements of degradation at the object scale (μm)

Health organizations now recommend diversifying and increasing our dietary intake of polyunsaturated fatty acids (PUFA) omega-3, which are essential for the proper functions of our cells. To meet these recommendations, plant membranes, and in particular photosynthetic membranes, represent a real potential, as they contain specific lipids, and in particular galactolipids, whose degradation by enzymatic reactions provides PUFA omega-3. Due to their particular composition, these systems present phase coexistences and thus lateral heterogeneity impacting their digestibility. In order to optimally exploit plant lipid sources, it is necessary to understand their fate in the human gastrointestinal tract.

The results obtained in this research work provide an in-depth understanding of the mechanisms of interaction between digestive enzymes and plant membrane assemblies. In particular, this work is the first to investigate the digestion of heterogeneous monolayers of galactolipids and phospholipids by close analogues of the main enzymes responsible for the gastrointestinal degradation of plant lipids in humans. The originality of this study is based on a thorough characterization of the interfacial behavior of plant lipid systems, presenting a chemical heterogeneity inducing a physical heterogeneity. The digestibility of these heterogeneous plant lipid assemblies was studied at the molecular scale, but also at the micronic object scale.

This work allowed to report the substrate specificity of the studied lipases and phospholipases (rDGL, sPLA2-IB, gPLRP2) on plant polar lipids. In particular, the galactolipase, but also phospholipase A1 activities of gPLRP2 were observed in heterogeneous galactolipid and phospholipid systems. The genericity of action of these enzymes with respect to the physical state of the membranes has also been demonstrated. We demonstrate here that at the lipid interfaces, a high content of polyunsaturated acyl groups can amplify the local compressibility and be an asset for the insertion of digestive lipases. This physical aspect remains to be confronted with the chemical specificity of the enzyme. Overall, plant lipid assemblies are rich in polar lipids and particularly galactolipids, which concentrate significant quantities of omega-3 PUFA, and are bioaccessible under model conditions under the action of gPLRP2. These assemblies also exhibit surface-active and oxidative stability properties characterized in this work. The galactolipase activity of PLRP2 at the level of modulable model membrane monolayers, but also at the level of natural membrane assemblies, opens the way to the development of plant-based dietary alternatives to vectorize omega-3 PUFA, and contribute to rebalancing human and animal diets.


 Jury members

PhD supervisors : Véronique VIE (Associate Professor, Université de Rennes 1), Claire BOURLIEU-LACANAL (Researcher, INRAE Montpellier).

Rapporteurs : Marie-Caroline MICHALSKI (Senior Researcher, Institut CarMeN, Lyon), Éric MARECHAL (Senior Researcher, CNRS, CEA Grenoble).

Examinators : Isabelle CANTAT (Professor, Université de Rennes 1), Jacques FATTACCIOLI (Associate Professor, Université Pierre et Marie Curie, Paris).

Invited members : Frédéric CARRIERE (Senior Researcher, CNRS, IMM Marseille), Tim WOOSTER (Group leader, Nestlé Research Center, Lausanne, Switzerland).