Electrospray ionization mass spectrometry, circular dichroism and SAXS studies of the (S)-hydroxynitrile lyase from Hevea brasiliensis

We report on experiments pertaining to solution properties of the (S)-hydroxynitrile lyase from Hevea brasiliensis (HbHNL). Small angle X-ray scattering unequivocally established the enzyme to occur in solution as a dimer, presumably of the same structure as in the crystal. The acid induced, irreversible deactivation of HbHNL was examined by electrospray ionization mass spectrometry (ESI-MS), circular dichroism (CD) and by measuring the enzyme activity. The deactivation is paralleled by an unfolding of the enzyme. ESI-MS of this 30000 Da per monomer heavy protein demonstrated that unfolding took place in several stages which are paralleled by a decrease in enzyme activity. Unfolding can also be observed by CD spectroscopy, and there is a clear correlation between enzyme activity and unfolding as detected by ESI-MS and CD.