The present invention relates to a chemically modified mutant protein including
a cysteine residue substituted for a residue other than cysteine in a precursor
protein, the substituted cysteine residue being subsequently modified by reacting
the cysteine residue with a glycosylated thiosulfonate. Also, a method of producing
the chemically modified mutant protein is provided. The present invention also
relates to a glycosylated methanethiosulfonate. Another aspect of the present invention
is a method of modifying the functional characteristics of a protein including
providing a protein and reacting the protein with a glycosylated methanethiosulfonate
reagent under conditions effective to produce a glycoprotein with altered functional
characteristics as compared to the protein. In addition, the present invention
relates to methods of determining the structure-function relationships of chemically
modified mutant proteins.