Site-Specific Synthesis of Cysteine-Bridged Glycoproteins via Expressed Protein Glycoligation.

Nicholas Holloran, Daniel Collins, Upendra Rathnayake, Bixia Zhang, Minseob Koh, ChulHee Kang, Philip Garner

Bioconjugate chemistry 2020 Oct 21

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Site-specific glycosylation of a functional recombinant protein thioester is reported. The thioester functionalized protein sfGFP-Y151ThioD, prepared by genetic code expansion, underwent native chemical ligation with the cysteine-conjugated glycans H-Cys-NH-GlcNAc and H-Cys-NH-(GlcNAc)2(Man)3 to give the corresponding cysteine-bridged glycoproteins. The intact glycoproteins, which retained their fluorescence, were characterized by top-down mass spectrometry and gel electrophoresis. The bridging cysteine provided a convenient handle for affinity chromatography purification of the glycoproteins via a removable biotin tag. Given the influence that specific glycoforms can have on a protein's function, the ability to attach a homogeneous glycan to an intact protein in a functional group controlled yet sequon-independent manner could find widespread application. These preliminary results set the stage for development of the expressed protein glycoligation (EPG) concept.

Citation

Nicholas Holloran, Daniel Collins, Upendra Rathnayake, Bixia Zhang, Minseob Koh, ChulHee Kang, Philip Garner. Site-Specific Synthesis of Cysteine-Bridged Glycoproteins via Expressed Protein Glycoligation. Bioconjugate chemistry. 2020 Oct 21;31(10):2362-2366