The structures of the catalytic domains of the bacterial non-Leloir glycosyl-transferases of glycoside hydrolase family 17 (GH17) from Pseudomonas aeruginosa (Glt1), P. putida (Glt3), Azotobacter vinelandii (Glt7) and Bradyrhizobium japonicum (Glt20) were obtained by molecular modeling. Hybrid models of the enzymes were built and the stability of the modeled TIM-barrel structures will be supported by molecular dynamics simulations. The potential catalytic amino-acids (corresponding to E120 and E209 in Glt20) are in all models conserved at positions corresponding to those in structure determined GH17 candidates. The single mutants E120Q and E209Q, were constructed for Glt20, resulting in variants with no detectable activity, confirming the importance of the respective residue for function. Docking of ligands allowed prediction of sub-site interactions, and suggests that the substrates bind in the same orientation in non-reducing end transglycosidases (Glt1, 3 and 7) and reducing end transglycosidase (Glt20). The studies will allow us to present a putative mechanism for transglycosylation in both non-reducing and reducing end proteobacterial non-Leloir glycosyltransferases.