Enhanced Hydrolytic Stability of Short‐Chain Poly[(R)‐3‐hydroxybutyrate] Conjugated to Native E. coli Cytoplasmic Proteins

Many prokaryotic and eukaryotic proteins are modified by post‐translational conjugation to short‐chain poly[(R)‐3‐hydroxybutyrate] (cPHB). The relative lability of ester bonds raises the concern that the cPHB may be substantially degraded by chemical hydrolysis during protein purification, thus increasing the difficulty of its detection and measurement. Here, we compare rates of acid‐ and base‐catalyzed hydrolysis of cPHB conjugated to native and denatured proteins at room temperature. E. coli cytoplasmic proteins, native or denatured by addition of guanidium hydrochloride, were treated with aqueous solutions of H₂SO₄ or NaOH at concentrations ranging from 0.1–2.0n . The loss of cPHB was measured as a function of time by a chemical assay. We find that cPHB conjugated to native proteins is surprisingly resistant to both acid‐ and base‐catalyzed hydrolysis, whereas cPHB conjugated to denatured proteins is proficiently degraded at rates proportional to acid or base concentration. The results suggest that cPHB occupies a highly protective environment within native proteins.