Proteolysis targeting chimeras (PROTACs), heterobifunctional
protein
degraders, have emerged as an exciting and transformative technology
in chemical biology and drug discovery to degrade disease-causing
proteins through co-opting of the ubiquitin–proteasome system
(UPS). Here, we develop a mechanistic mathematical model for the use
of irreversible covalent chemistry in targeted protein degradation
(TPD) either to a target protein of interest (POI) or an E3 ligase
ligand, considering the thermodynamic and kinetic factors governing
ternary complex formation, ubiquitination, and degradation through
the UPS. We highlight key advantages of covalency to the POI and E3
ligase and the underlying theoretical basis in the TPD reaction framework.
We further identify regimes where covalency can serve to overcome
weak binary binding affinities and improve the kinetics of ternary
complex formation and degradation. Our results highlight the enhanced
catalytic efficiency of covalent E3 PROTACs and thus their potential
to improve the degradation of fast turnover targets.