This superfamily contains proteins similar to the RmlC (dTDP (deoxythymidine diphosphates)-4-dehydrorhamnose 3,5-epimerase)-like cupins. RmlC is a dTDP-sugar isomerase involved in the synthesis of L-rhamnose, a saccharide required for the virulence of some pathogenic bacteria. Cupins are a functionally diverse superfamily originally discovered based on the highly conserved motif found in germin and germin-like proteins. This conserved motif forms a beta-barrel fold found in all of the cupins, giving rise to the name cupin ('cupa' is the Latin term for small barrel). The active site of members of this superfamily is generally located at the center of a conserved barrel and usually includes a metal ion. The different functional classes in this superfamily include single domain bacterial isomerases and epimerases involved in the modification of cell wall carbohydrates, two domain bicupins such as the desiccation-tolerant seed storage globulins, and multidomain nuclear transcription factors involved in legume root nodulation.
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