Evidence of emergence of "genuine" novel protein interactions by aa mutation Anyone knows of an example of a protein that, without coming from a recent duplication event, underwent a mutation(s) that caused it to have a novel interaction with a new ligand, substrate, other protein or molecule?
By novel I imply that it doesn't "go back" to an ancestral interaction or doesn’t develops an interaction that it's already performed by a close relative. 
I assume that these mutations are extremely rare, and that a duplicate is almost always necessary to have them fixed in a lineage.
HA Sialic acid receptor binding in influenza virus determining host specificity, viz. Bird flu vs human flu.