title: Strain-promoted alkyne-azide cycloadditions (SPAAC) reveal new features of glycoconjugate biosynthesis.
abstract: We have shown that 4-dibenzocyclooctynol (DIBO), which can easily be obtained by a streamlined synthesis approach, reacts exceptionally fast in the absence of a Cu(I) catalyst with azido-containing compounds to give stable triazoles. Chemical modifications of DIBO, such as oxidation of the alcohol to a ketone, increased the rate of strain promoted azide-alkyne cycloadditions (SPAAC). Installment of a ketone or oxime in the cyclooctyne ring resulted in fluorescent active compounds whereas this property was absent in the corresponding cycloaddition adducts; this provides the first example of a metal-free alkyne-azide fluoro-switch click reaction. The alcohol or ketone functions of the cyclooctynes offer a chemical handle to install a variety of different tags, and thereby facilitate biological studies. It was found that DIBO modified with biotin combined with metabolic labeling with an azido-containing monosaccharide can determine relative quantities of sialic acid of living cells that have defects in glycosylation (Lec CHO cells). A combined use of metabolic labeling/SPAAC and lectin staining of cells that have defects in the conserved oligomeric Golgi (COG) complex revealed that such defects have a greater impact on O-glycan sialylation than galactosylation, whereas sialylation and galactosylation of N-glycans was similarly impacted. These results highlight the fact that the fidelity of Golgi trafficking is a critical parameter for the types of oligosaccharides being biosynthesized by a cell. Furthermore, by modulating the quantity of biosynthesized sugar nucleotide, cells might have a means to selectively alter specific glycan structures of glycoproteins.
authors.affiliation: Complex Carbohydrate Research Center, University of Georgia, Athens, GA 30602, USA.
authors.forename: Ngalle Eric
authors.initials: NE
authors.lastname: Mbua
authors.forename: Jun
authors.initials: J
authors.lastname: Guo
authors.forename: Margreet A
authors.initials: MA
authors.lastname: Wolfert
authors.forename: Richard
authors.initials: R
authors.lastname: Steet
authors.forename: Geert-Jan
authors.initials: GJ
authors.lastname: Boons
mesh_terms: D000480:Alkynes / Q000737:chemistry* / Q000378:metabolism; D000818:Animals; D001386:Azides / Q000737:chemistry* / Q000378:metabolism; D016466:CHO Cells; D057930:Click Chemistry / Q000379:methods*; D006224:Cricetinae; D003412:Cricetulus; D006001:Glycoconjugates / Q000096:biosynthesis*; D006023:Glycoproteins / Q000737:chemistry / Q000378:metabolism; D006031:Glycosylation; D006056:Golgi Apparatus / Q000378:metabolism*; D006801:Humans; D019169:Jurkat Cells; D037102:Lectins / Q000378:metabolism; D015336:Molecular Probe Techniques; D019158:N-Acetylneuraminic Acid / Q000378:metabolism; D011134:Polysaccharides / Q000378:metabolism; D021381:Protein Transport / Q000502:physiology; D013050:Spectrometry, Fluorescence; D013194:Staining and Labeling / Q000379:methods*; D014230:Triazoles / Q000737:chemistry
chemical_list: D000480:Alkynes; D001386:Azides; D006001:Glycoconjugates; D006023:Glycoproteins; D037102:Lectins; D011134:Polysaccharides; D014230:Triazoles; D019158:N-Acetylneuraminic Acid