Fig. 5.

EnvSia156 proposed catalytic mechanism. a Proposed inverting mechanism for EnvSia156 with Asp14 acting as the general catalytic base and His134 as the acid catalyst. b Structure of the EnvSia156–Neu5Ac complex highlighting the two putative catalytic residues (Asp14 and His134), the carboxylate-coordinating triad (Arg129, Arg202, Asn346) and the hydrophobic pocket that possibly constitutes the +1 binding site (Trp164, Phe203, Trp279, Phe278). c Schematic representation of the Neu5Ac bound to EnvSia156 −1 binding sub-site, showing all the hydrogen bond interactions between both molecules