Retaining glycosyl hydrolases, mechanism

A. White and D. R. Rose, Mechanism of catalysis by retaining p-glycosyl hydrolases, Curr. Opin. 

White, A. and Rose, D.R. (1997) Mechanism of catalysis by retaining P-glycosyl hydrolases. Curr Opin Struct Biol, 7, 645-651... 

The recent burst of reported GT structures has shed light on their substrate binding and catalytic mechanisms. GTs are thought to use mechanistic strategies that directly parallel those used by the well characterised glycosyl hydrolases. However, while the mechanism of inverting GTs appears to be widely accepted, the mechanism of retaining enzymes remains a topic of considerable debate. These aspects will be discussed later in the chapter. 

Fig. 9. Glycosyl hydrolysis - retaining mechanism. The charged acidic acid residue in the active site of a retaining glycoside hydrolase nucleophilically attacks the glycosidic bond while an opposing protonated residue donates the necessary proton. The covalently bound intermediate product is released by a second nucleophilic attack by a water molecule activated by electrostatic repulsion from the recently de-protonated residue...

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