title: Biosynthetic incorporation of unnatural sialic acids into polysialic acid on neural cells.
abstract: In this study we demonstrate that polysialyltransferases are capable of accepting unnatural substrates in terminally differentiated human neurons. Polysialyltransferases catalyze the glycosylation of the neural cell adhesion molecule (NCAM) with polysialic acid (PSA). The unnatural sialic acid analog, N-levulinoyl sialic acid (SiaLev), was incorporated into cell surface glycoconjugates including PSA by the incubation of cultured neurons with the metabolic precursor N-levulinoylmannosamine (ManLev). The ketone group within the levulinoyl side chain of SiaLev was then used as a chemical handle for detection using a biotin probe. The incorporation of SiaLev residues into PSA was demonstrated by protection from sialidases that can cleave natural sialic acids but not those bearing unnatural N-acyl groups. The presence of SiaLev groups on the neuronal cell surface did not impede neurite outgrowth or significantly affect the distribution of PSA on neuronal compartments. Since PSA is important in neural plasticity and development, this mechanism for modulating PSA structure might be useful for functional studies.
authors.affiliation: Departments of Chemistry and Molecular and Cell Biology, University of California, and Center for Advanced Materials, Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.
authors.forename: N W
authors.initials: NW
authors.lastname: Charter
authors.forename: L K
authors.initials: LK
authors.lastname: Mahal
authors.forename: D E
authors.initials: DE
authors.lastname: Koshland
authors.forename: C R
authors.initials: CR
authors.lastname: Bertozzi
mesh_terms: D002451:Cell Compartmentation; D002454:Cell Differentiation; D002462:Cell Membrane / Q000378:metabolism; D003569:Cytidine Monophosphate N-Acetylneuraminic Acid / Q000378:metabolism; D006001:Glycoconjugates / Q000096:biosynthesis; D006595:Hexosamines / Q000378:metabolism; D006801:Humans; D019006:Neural Cell Adhesion Molecules / Q000096:biosynthesis; D009474:Neurons / Q000166:cytology / Q000378:metabolism*; D011134:Polysaccharides / Q000378:metabolism*; D012794:Sialic Acids / Q000378:metabolism*; D012799:Sialyltransferases / Q000378:metabolism*; D013379:Substrate Specificity; D014407:Tumor Cells, Cultured
chemical_list: D006001:Glycoconjugates; D006595:Hexosamines; C105871:N-levulinoyl mannosamine; C115916:N-levulinoylsialic acid; D019006:Neural Cell Adhesion Molecules; D011134:Polysaccharides; D012794:Sialic Acids; D003569:Cytidine Monophosphate N-Acetylneuraminic Acid; C046778:CMP-N-acetylneuraminate-poly-alpha-2,8-sialosyl sialyltransferase; D012799:Sialyltransferases