The Active Site of Endosialidase

The amino acid His-350 is located in a position similar to the general acid/base aspartic acid of exosialidases (Fig. 3a Nani 291) and has been mutated to alanine for co-crystaUization with DP5 [106]. In comparison to wild type endoNF, the alanine residue red in Fig. 3a) H350A perfectly superposes with the Ca and C(5 atoms of the histidine residue. Thus, the backbone of the p-propeller is not affected by this mutation. In the H350A mutant, a trimeric sialic acid (DP3) is bound in the active site coordinated by a network of water molecules and polar contacts (Fig. 3c). The geometry of the active site constrains the otherwise helical polysialic acid into an extended conformation (see Sect. 8 for heUcal epitopes). 

Active site residue In endoNF In endoNA/endoNE Function 

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Jakobsson E, Jokilammi A, Aalto J, Ollikka P, Lehtonen IV, Hirvonen H, Finne J (2007) Identification of amino acid residues at the active site of endosialidase that dissociate the poly sialic acid binding and cleaving activities in Escherichia coli K1 bacteriophages. Biochem J 405 465-472... 

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