Fusion protein construct

A method comprising

• (a) contacting a first fusion protein comprising an affinity reagent and a reactive enzyme comprising cutinase with a linker comprising a functional group specific for irreversibly inhibiting the first fusion protein reactive enzyme at a first terminus thereby coupling the first fusion protein reactive enzyme and the linker at the first terminus, and
• (b) contacting a second fusion protein comprising an affinity reagent and a reactive enzyme comprising HaloTag or SnapTag with a second terminus of the linker, the second terminus of the linker comprising a functional group specific for irreversibly inhibiting the second fusion protein reactive enzyme thereby coupling the second fusion protein reactive enzyme and the linker at the second terminus,
• thereby forming a construct comprising the first fusion protein coupled to the linker through the reactive enzyme of the first fusion protein and the functional group specific for irreversibly inhibiting the reactive enzyme of the first fusion protein and the second fusion protein coupled to the linker through the reactive enzyme of the second fusion protein and the functional group specific for irreversibly inhibiting the reactive enzyme of the second fusion protein;
• wherein the first fusion protein affinity reagent and the second fusion protein affinity reagent each comprise an antibody or fragment thereof,
• wherein the antibody fragment comprises Fab′ fragments, F(ab)2 fragments, Fv fragments, Fc fragments, one or more complementarity determining regions (CDR) fragments, an individual heavy chain, an individual light chain, or a dimeric heavy and light chain.