Stabilization of a supplemental digestive enzyme by post-translational engineering using chemically-activated polyethylene glycol

Many enzymes used as digestive aids exhibit, at best, moderate stability when incubated under gastrointestinal conditions. A supplemental β-galactosidase administered orally to treat lactose intolerance was conjugated to 40 kDa, branched polyethylene glycol (PEG). PEGylation increased the enzyme's relative activity at lower pH values (2.5-4.5) and doubled enzyme stability at pH 2.5. The PEGylated enzyme retained significantly more residual activity after exposure to simulated gastric conditions (52% versus 31%), a consequence of protection from both pepsin and low pH mediated inactivation. Conjugation also provided significant protection against the proteolytic component of pancreatin. Overall, the PEGylated enzyme retained over twice the levels of residual activity recorded for non-PEGylated enzyme after exposure to complete simulated gastrointestinal conditions. PEGylation also marginally improved the enzyme's kinetic characteristics. When using its physiological substrate (lactose), K_m values recorded were slightly decreased (from 83 to 60 μM) and k_cat/K_m values (M^-1 s^-1) were increased from 100 to 147. This appears to be the first report of the use of a conjugated PEG to stabilize a digestive enzyme and the first report of the ability of conjugated PEG to stabilize a protein at low pH.