The present invention relates to a process for the enzymatic modification of a
glycoprotein. The process comprises the step of contacting a
glycoprotein comprising a
glycan comprising a terminal GlcNAc-
moiety, in the presence of
glycosyltransferase that is, or is derived from, a β-(1,4)-N-acetylgalactosaminyltransferase, with a non-natural
sugar-derivative
nucleotide. The non-natural
sugar-derivative
nucleotide is according to formula (3): wherein A is selected from the group consisting of —N3, —C(O)R3, —(CH2)iC≡C—R4, —SH, —SC(O)R8, —SC(0)OR8, —SC(S)OR8, —F, —CI, —Br —I, —OS(O)2R5, terminal C2-C24 alkenyl groups, C3-C5 cycloalkenyl groups, C4-C8 alkadienyl groups, terminal C3-C24 allenyl groups and amino groups. The invention further relates to a
glycoprotein obtainable by the process according to the invention, to a bioconjugate that can be obtained by conjugating the glycoprotein with a
linker-conjugate, and to β-(1,4)-N-acetylgalactosaminyltransferases that can be used in preparing the the glycoprotein according to the invention.