REMARKABLE DESTABILIZATION OF RECOMBINANT ALPHA-LACTALBUMIN BY AN EXTRANEOUS N-TERMINAL METHIONYL RESIDUE

A recombinant bovine alpha-lactalbumin, possessing an additional N-ter minal methionyl residue, was expressed in Escherichia coli. In order t o address the effects of the N-terminal methionyl residue on conformat ional stability, the thermal stability of the recombinant alpha-lactal bumin was investigated by measuring temperature-dependence of circular dichroism spectra, and it was compared with that of authentic alpha-l actalbumin from bovine milk. The thermal stability of the recombinant alpha-lactalbumin was significantly lower than that of authentic alpha -lactalbumin. The enthalpy change of unfolding of the recombinant prot ein was found to be the same as that of the authentic one when compare d at the same temperature. Therefore, the N-terminal methionyl residue seems to destabilize the conformation of recombinant alpha-lactalbumi n through some entropic effects.