Sandbox UNLPam 7

The crystal structure of the GH78 family a-rhamnosidase from Klebsiella oxytoca (KoRha) has been determined at 2.7 A °

resolution with rhamnose bound in the active site of the catalytic domain. Curiously, the putative catalytic acid, Asp 222, is preceded by an unusual non-proline cis-peptide bond which helps to project the carboxyl group into the active centre. This KoRha homodimeric structure is significantly smaller than those of the other previously determined GH78 structures. Nevertheless, the enzyme displays a-rhamnosidase activity when assayed in vitro, suggesting that the additional structural domains found in the related enzymes are dispensible for function.

== Function == a-L-rhamnose is found in plants and bacteria

as components of polysaccharides, such as pectins,2 and the O antigen polysaccharides, responsible for determining the antigenicity of pathogenic bacteria3; it is also found in rhamnolipids4 and it is attached to small molecule natural products, such as rutin. There is industrial interest in arhamnosidases for use in the debittering of citrus juices and for the release of flavonoids from rhamnosylated precursors; in wine production they play a role in the hydrolysis of glycosylated terpene aroma compounds.5 In the context of expanding and diversifying the suite of enzymes available to us for carbohydrate biotransformations,6–13 we were drawn to consider a-rhamnosidases. In the CAZy database,14 rhamnosidases are currently classified into GH28 pectin hydrolases, GH78 containing exclusively rhamnosidases, and GH106 containing a single enzyme from Sphingomonas

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Structural highlights

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