Aga1, the first alpha-Galactosidase from the human bacteria Ruminococcus gnavus E1, efficiently transcribed in gut conditions

Differential gene expression analysis was performed in monoxenic mice colonized with Ruminococcus gnavus strain E1, a major endogenous member of the gut microbiota. RNA arbitrarily primed-PCR fingerprinting assays allowed to specifically detect the in vivo expression of the aga1 gene, which was further confirmed by RT-PCR. The aga1 gene encoded a protein of 744 residues with calculated molecular mass of 85,207 Da. Aga1 exhibited significant similarity with previously characterized α-Galactosidases of the GH 36 family. Purified recombinant protein demonstrated high catalytic activity (104 ± 7 U mg−1) and efficient p-nitrophenyl-α-d-galactopyranoside hydrolysis [kcat/Km = 35.115 ± 8.82 s−1 mM−1 at 55 °C and kcat/Km = 17.48 ± 4.25 s−1 mM−1 at 37 °C].