Thermostability of doubly glycosylated recombinant lysozyme.

We prepared a lysozyme mutant (Q41S/R61S) introducing Asn-type glycosylation signal sites by yeast expression system. On purification by cation exchange column at pH 7, three fractions were obtained. Peptide mapping and mass-spectrometry showed the fractions were the derivatives glycosylated at both Asn39 and Asn59, at only Asn39, and not glycosylated. It was revealed that the processing of Asn-linked oligosaccharide at Asn39 and Asn59 occurred independently in yeast cells. The denaturation temperatures of these derivatives by differential scanning calorimetry were 76.0, 68.8, and 67.5 degrees C at pH 3, respectively. The stabilization of glycosylated lysozyme depends on the degree of glycosylation. We concluded that stabilized proteins can be constructed by glycosylation at proper sites. Thermodynamic stabilization by the artificial double glycosylations on a protein has not yet been reported.