The Many Activities of GH

Between the nucleophilic and acid-base glutamates in the linear sequence lies a catalytically important assisting aspartate. GH 16 can be divided into two sub-families. The first, including laminarases and agarases, has an active site linear sequence Glu(nucleophile)-Hph-Asp(assist)-Hph-Met-Glu(acid/base), where Hph is a hydrophobic amino acid such as isoleucine. The second subfamily does not possess the methionine. The X-ray structures of the enzymes indicate that this extra Met residue distorts a p-strand to make a p-bulge . 

Whereas GH 20 contains hexosaminidases and chitobiosidases i.e. enzymes with —1 and possibly +1 subsites only), GH 18 contains chitinases, enzymes which act at the polymer level. X-ray crystallographic evidence for amide 

The protonated oxazolidines are comparatively strong acids (2-methyl-A -oxazoline has a pifa of 5.5, which the electron-withdrawing substituents in the sugar will lower), and in GH and GH 20 active site aspartates 

The enzymes which hydrolyse the GlcNAc residue attached to Ser or Thr of glycoproteins have no sequence similarity to GH 20, but it appears that GH 84, 

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