Charge-Preserving Atom Transfer Radical Polymerization Initiator Rescues the Lost Function of Negatively Charged Protein–Polymer Conjugates

When grown from the surface of proteins, negatively charged polymers cause irreversible inactivation, thereby limiting the breadth of the synthetic space that negatively charged protein–polymer conjugates can be applied to. More broadly speaking, independent of polymer and synthetic approach, almost all protein–polymer conjugates are less active than their precursors. After more than a decade without major advances in understanding why the attachment of some polymers so sharply deactivates enzymes, we focused our attention on a technique to protect enzymes from the growth of a deactivating polymer by restoring the charge at the protein surface during polymer attachment. We synthesized an amino-reactive positively charged atom transfer radical polymerization initiator that inserted a permanent positive charge at the site of bio-macroinitiator attachment. Preserving the surface charge through attachment of the permanent positively charged initiator led to the first observation of activity of enzymes that we...