Biophysical characterization of a recombinant leucyl aminopeptidase from Bacillus kaustophilus

The biophysical properties of Bacillus kaustophilus leucyl aminopeptidase (BkLAP) were examined in terms of analytical ultracentrifugation, fluorescence spectroscopy, and circular dichroism. By using the analytical ultracentrifuge, we demonstrated that tetrameric BkLAP exists as the major form in solution at protein concentration of 1.5 mg/ml at pH 8.0. The native enzyme started to unfold beyond ∼1 M GdnHCl and reached an unfolded intermediate with [GdnHCl]1/2 at 1.8 M. Thermal unfolding of BkLAP was found to be highly irreversible and led to a marked formation of aggregates.