For nearly 40 years, therapeutic proteins have been stabilized by chemical conjugation of polyethylene glycol (PEG), but recently zwitterionic materials have proved to be a more effective substitute. In this work, we demonstrate that genetic fusion of alternating-charge extensions consisting of anionic glutamic acid (E) and cationic lysine (K) is an effective strategy for protein stabilization. This bioinspired "EKylation" method not only confers the stabilizing benefits of poly(zwitterions) but also allows for rapid biosynthesis of target constructs. Poly(EK) peptides of different predetermined lengths were appended to the C-terminus of a native beta-lactamase and its destabilized TEM-19 mutant. The EK-modified enzymes retained biological activity and exhibited increased stability to environmental stressors such as high temperature and high-salt solutions. This one-step strategy provides a broadly applicable alternative to synthetic polymer conjugation that is biocompatible and degradable.