Situation of monomethoxypolyethylene glycol covalently attached to lysozyme.

We selectively introduced monomethoxypolyethylene glycol (mPEG) 5000, 2000, and 550 into Asp119 in lysozyme. To examine how the mPEGs were present on the surface of the modified lysozyme, the activities, binding abilities to the Fab fragment of anti-lysozyme monoclonal antibody, net charges and nuclear magnetic resonance (NMR) spectra of mPEG lysozymes were examined. With the increase in molecular weight of mPEG, the activities and binding abilities to the Fab of mPEG lysozyme decreased. However, introduced mPEG5000 did not cause complete inhibition of the activities and binding abilities to the Fab, while the maximum length of mPEG5000 was so great that it largely covered the surface of the lysozyme molecule. Analyses of the net charges and NMR suggested that the introduced mPEG preferentially assumed a folded conformation on the surface rather than spread all over the surface. Based on the structure of mPEG lysozyme, the mechanism of the reduced immunogenicity of mPEG lysozyme was discussed.