Provided herein are methods and recombinant expression systems for the production of recombinant glycoproteins that have increased sialic acid content and contain predominantly alpha2-6 sialic acid linkages. Also provided herein are recombinant glycoproteins that have an increased in vivo circulatory half-life. One potential application of the glycoproteins described herein is for the treatment and prophylaxis of poisoning by neurotoxins.