Isabelle André, Josette Perrier, Mickael Lafond, Frédérique Pompeo, Nicolas Vidal, Alexandra S. Tauzin, Vincent Lombard, Jérémy Esque, Thierry Giardina, Laetitia Bruel, Gabrielle Potocki-Véronèse, Nathalie Quinson, Elisabeth Laville, Michel Fons, Institut des Sciences Moléculaires de Marseille (ISM2), Aix Marseille Université (AMU)-École Centrale de Marseille (ECM)-Institut de Chimie du CNRS (INC)-Centre National de la Recherche Scientifique (CNRS), Toulouse Biotechnology Institute (TBI), Institut National des Sciences Appliquées - Toulouse (INSA Toulouse), Institut National des Sciences Appliquées (INSA)-Université de Toulouse (UT)-Institut National des Sciences Appliquées (INSA)-Université de Toulouse (UT)-Centre National de la Recherche Scientifique (CNRS)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE), Architecture et fonction des macromolécules biologiques (AFMB), Aix Marseille Université (AMU)-Centre National de la Recherche Scientifique (CNRS)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE), Institut de Chimie Radicalaire (ICR), Aix Marseille Université (AMU)-Institut de Chimie du CNRS (INC)-Centre National de la Recherche Scientifique (CNRS), Laboratoire de chimie bactérienne (LCB), Aix Marseille Université (AMU)-Centre National de la Recherche Scientifique (CNRS), Bioénergétique et Ingénierie des Protéines (BIP ), European Project: 707457,H2020,H2020-MSCA-IF-2015,CaTSYS(2016), Aix Marseille Université (AMU)-Centre National de la Recherche Scientifique (CNRS)-École Centrale de Marseille (ECM)-Institut de Chimie du CNRS (INC), Institut National des Sciences Appliquées (INSA)-Institut National des Sciences Appliquées (INSA)-Centre National de la Recherche Scientifique (CNRS)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE), and Centre National de la Recherche Scientifique (CNRS)-Aix Marseille Université (AMU)
International audience; Plant a-galactosides belonging to the raffinose family oligosaccharides (RFOs) and considered as prebiotics, are commonly degraded by a-galactosidases produced by the human gut microbiome. In this environment, the Ruminococcus gnavus E1 symbiont–well-known for various benefit–is able to produce an original RgAgaSK bifunctional enzyme. This enzyme contains an hydrolytic a-galactosidase domain linked to anATP dependent extra-domain, specifically involved in the a-galactoside hydrolysis and the phosphorylation of the glucose, respectively. However, the multi-modular relationships between both catalytic domains remained hitherto unexplored and has been, consequently, herein investigated. Biochemical characterization of heterologously expressed enzymes either in full-form or in separated domains revealed similar kinetic parameters. These results were supported by molecular modeling studies performed on the whole enzyme in complex with different RFOs. Further enzymatic analysis associated with kinetic degradation of various substrates followed by high pressure anionic exchange chromatography revealed that catalytic efficiency decreased as the number of D-galactosyl moieties branched onto the oligosaccharide increased, suggesting a preference of RgAgaSK for RFO’s short chains. A wide prevalence and abundance study on a human metagenomic library showed a high prevalence of the RgAgaSK encodinggene whatever the health status of the individuals. Finally, phylogeny and synteny studies suggested a limited spread by horizontal transfer of the clusters’ containing RgAgaSK to only few species of Firmicutes, highlighting the importance of these undispersed tandem activities in the human gut microbiome.