Increased elongation of N-acetyllactosamine repeats in doubly glycosylatedlysozyme with a particular spacing of the glycosylation sites

Lysozyme is an example of an extensively studied secretory enzyme. Glycosyl ated mutant human lysozyme has been used as a model in studies on the biosy nthesis of N-acetyllactosamine repeats in N-linked oligosaccharides. We exa mined the biosynthesis of the repeats in two doubly glycosylated mutants an d describe here a rapid purification and separation of singly and doubly gl ycosylated molecules. In one of the mutants, the elongation of the repeats is enhanced if the molecules are doubly glycosylated, but not if the carboh ydrate is attached to either site individually. This enhancement is not see n in the other doubly glycosylated mutant. Since lysozyme is not structural ly related to glycoproteins bearing carbohydrate with N-acetyllactosamine r epeats, we propose that in multivalent substrates the synthesis of the repe ats can be promoted by a proper spacing of the elongated carbohydrate anten nae in addition to any role of the protein backbone.