Methods for introducing mannose 6-phosphate and other oligosaccharides onto glycoproteins and applications thereof
Methods to introduce highly phosphorylated mannopyranosyl oligosaccharide derivatives containing mannose-6-phosphate (M6P), or other oligosaccharides bearing other terminal hexoses, to carbonyl groups on oxidized glycans of glycoproteins while retaining their biological activity are described. The methods are useful for modifying glycoproteins, including those produced by recombinant protein expression systems, to increase uptake by cell surface receptor-mediated mechanisms, thus improving their therapeutic efficacy in a variety of applications.
1. A method of coupling a beta-glucuronidase to an oligosaccharide comprising a phosphorylated mannose, comprising:
(a) derivatizing an oligosaccharide comprising a phosphorylated mannose with a compound containing a carbonyl-reactive group;
(b) oxidizing a beta-glucuronidase having at least one oligosaccharide to generate at least one carbonyl group on the at least one oligosaccharide of the beta-glucuronidase, wherein less than or equal to about 10 mM periodate is used to oxidize one or more sialic acid residues on the beta-glucuronidase; and
(c) reacting the derivatized oligosaccharide with the oxidized beta-glucuronidase,
thereby coupling the oligosaccharide to the beta-glucuronidase.
2. The method of claim 1 , wherein the oligosaccharide comprising the phosphorylated mannose is a biantennary mannopyranosyl oligosaccharide.
3. The method of claim 2 , wherein the biantennary mannopyranosyl oligosaccharide comprises bis-mannose 6 phosphate (M6P).
4. The method of claim 1 , wherein the oligosaccharide comprising the phosphorylated mannose comprises a compound having the formula 6-P-M n -R wherein:
M is a mannose or mannopyranosyl group;
P is a phosphate group linked to the C-6 position of M;
R comprises a chemical group containing a carbonyl-reactive group, and
n is an integer from 1-15, wherein if n>1, M n are linked to one another by alpha (1,2), alpha (1,3), alpha (1,4), or alpha (1,6).
5. A method of claim 4 , wherein the oligosaccharide comprising the phosphorylated mannose comprises one of M6P, phosphopentamannose derived from Hansenula holstii O-phosphomannan, and 6-P-M-(alpha 1,2)-M(alpha 1,2)-M.
6. The method of claim 1 , wherein the carbonyl-reactive group is a hydrazine, a hydrazide, an aminooxy, or a semicarbazide.
7. A conjugate comprising a beta-glucuronidase coupled to an oligosaccharide comprising a phosphorylated mannose, prepared by the method of claim 1 .