 The researchers for this study decided to use CuAAC, despite the purpose of this research to have in-vivo applications, for a few reasons.First, the likelihood for copper to be bound by the formula_1 protein is low due to the presence of only 2 glutamic acid residues and no histidine residues (two residues with a high affinity for Cu(I)).These residues are present in the thioredoxin; which is the solubilizing fusion partner conjugated to the 4RepCT protein during synthesis.