Specificity or function swapping
The segregation of different functionalities to different domains allows the swapping of functionalities trough the swapping of domains. The NAD (nicotinaminde adenine dinucleotide) dependant dehydrogenases provide a nice example of this. The dinucleotide binding domains of these enzymes, which have a alpha/beta doubly-wound topology known as the Rossman fold, are similar but their substrate binding domains are different allowing differences in specificity.
A few examples:
1. NAD-dependant dehydrogenases
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