Crystal Structure of Endosialidase

The crystal structure of the catalytic part of endoNF (amino acids 246-910) has been solved in three studies [12,106,113] (Table 3). First, the protein structure has been solved in its apo state and with bound substrate after soaking of sialic acid trimer. By this means, two oligosialic acid binding sites have been identified [12] (see Fig. 2c and Sect. 8). To allow identification of longer sialic acid oligomers bound to endoNF, two active site mutants have been created upon structural information from the first structure [106]. Finally, an endoNF structure has been solved at the high resolution of 0.98 A [113]. 

EndoNF variant Wild type Wild type Wild type R647A H350A Wild type 

PDB ID IVOE IVOF 3GVL 3GVJ 3GVK 3JU4 

Substrate [A] — DP3 Observed sialic acid oligomer DP3 DP5 DP5t DP3  

As in exosialidases, the p-propeller green) of endoNF contains the catalytic site a, Fig. 2c) which is located in a wide cleft in its center (see Sect. 7) and was found to share a higher structural similarity with bacterial and eukaryotic rather than viral exosialidases [12]. 

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