GH 15 Glucoamylase

It is clear that interactions in the +1 site, as with many inverting enzymes, are important a-glucopyranosyl fluoride is a mere 100-fold better substrate than maltose, despite being intrinsically much more reactive. Interactions with the 4-OH of the +1 sugar of isomaltose appear to account to its susceptibility to the enzyme, as well as maltose. Interactions with the 4 and 6 hydroxyls of both isomaltose and maltose in the —1 subsite was crucial for catalysis, as shown both by deoxygenation and site-directed mutagenesis.  

The early literature on this enzyme reports many attempts to analyse its interactions with oligosaccharides in terms of the Hiromi subsite analysis. These are now known to be flawed because of the implausible assumptions 

S GH 48. This family appears to form a clan with GH 8, with the protein fold (a/a)g. The cellobiohydrolase from C. thermocellum has the expected tunnel, with eight monosaccharide binding sites and is processive. 

The excision of nucleic acid bases by hydrolases can be both a repair mechanism for the host and an offensive weapon by competitors. There is a whole array of DNA repair glycosylases, some of which are merely hydrolases, others of which have an associated lyase activity.Catalysing a similar reaction are the proteins, formed in the seeds of many plants, which hydrolyse a ribosyl-adenine bond in the sequence GAGA loop region of the 28S RNA, thus shutting down protein synthesis.No direct determination of reaction stereochemistry has been carried out for either class of enzyme, nor is an X-ray structure of an enzyme-substrate-analogue complex available, but the crystal structures so far available suggest inversion. 

Nucleotide C-N bond hydrolysis and phosphorolysis at the monomer level form part of purine salvage pathways and their mechanisms have been intensively investigated for pharmacological reasons. Humans can biosynthesise purine nucleosides de novo, whereas protozoal parasites such as those causing bilharzia and Chagas disease rely on hydrolysis of preformed nucleosides from the host. Finally, a series of ribosyl transfers from NAD are important in the modification of proteins by pathogens and have been studied extensively. 

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