Mechanism of polyethylene glycol interaction with the molten globule folding intermediate of bovine carbonic anhydrase B.

Polyethylene glycol has been shown to bind to the molten globule intermediate on the bovine carbonic anhydrase B folding pathway. The mechanism of this interaction has been extensively probed. Polyethylene glycol (PEG) binds weakly to the molten globule first intermediate as measured by hydrophobic interaction chromatography, but PEG does not bind to either the native state or the second intermediate. The binding of PEG to the molten globule has been confirmed with both intrinsic fluorescence and fluorescence quenching experiments which indicate a single PEG-binding site on the molten globule. Electron paramagnetic resonance spectroscopic studies with nitroxide-labeled PEG also indicate a single binding site. Additional electron paramagnetic resonance studies with spin-labeled carbonic anhydrase B suggest that a conformational change occurs in the molten globule intermediate after PEG binds to the surface. The formation of a PEG-molten globule complex results in a reduction in self-association of this compact hydrophobic structure. PEG-molten globule complex formation is analogous to the observed interaction between chaperonins and a molten globule intermediate (Martin, J., Langer, T., Boteva, R., Schramel, A., Horwich, A.L., and Hartl, F.U. (1991) Nature 352, 36-42).