Many important biological processes are initiated by cell surface molecules, such as cell-cell adhesion and communication during development, virus-host cell binding, tumor cell metastasis and immunological recognition. Consequently, the ability to chemically control the display of epitopes on cell surfaces would enable a myriad of possibilities for studying cell-cell interactions and for engineering cells with novel properties. This presentation will focus on work in my laboratory that aims to apply the principles of organic chemistry to orchestrating cell surface chemistry. We have harnessed the cell's metabolic machinery to remodel cell surfaces with reactive organic functional groups. The foundation of our approach is the unnatural substrate tolerance of several enzymes involved in oligosaccharide biosynthesis, which permits the conversion of unnatural monosaccharide precursors into cell surface-associated oligosaccharides. We have exploited these pathways as vehicles for the delivery of uniquely reactive electrophilic functional groups, such as ketones and azides, to cell surfaces. For example, we demonstrated that an unnatural analog of N-acetylmannosamine bearing a ketone group, N-levulinoylmannosamine (ManLev), is metabolized by human cells to N-levulinoyl sialosides on the cell surface, resulting in the cell surface display of ketone groups. The cell surface can then be selectively reacted with rationally-designed organic structures bearing a complementary nucleophile such as an aminooxy group which reacts to form a stable covalent adduct. The ability to engineer chemical reactivity into endogenous cell surface molecules suggests many potential applications including the engineered adhesion of cells to materials and artificial surfaces.
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@footnote 1@ Mahal, L. K.; Yarema, K. J.; Bertozzi, C. R. Engineering Chemical Reactivity on Cell Surfaces Through Oligosaccharide Biosynthesis. Science 1997, 276, 1125-1128. @footnote 2@ Mahal, L. K.; Bertozzi, C. R. Engineered Cell Surfaces: Fertile Ground for Molecular Landscaping. Chemistry & Biology 1997, 4, 415-422. @footnote 3@ Lemieux, G. A. ; Bertozzi, C. R. Chemoselective Ligation Reactions with Proteins, Oligosaccharides and Cells. Trends Biotech. 1998, 16, 506-513. @footnote 4@Yarema, K. J.; Mahal, L. K.; Bruehl, R.; Rodriguez, E. C.; Bertozzi, C. R. Metabolic Delivery of Ketone Groups to Sialic Acid Residues. Application to Cell Surface Glycoform Engineering. J. Biol. Chem. 1998, 273, 31168-31179. @footnote 5@ Lemieux, G. A.; Yarema, K. J.; Jacobs, C. L.; Bertozzi, C. R. Exploiting Differences in Sialoside Expression for Selective Targeting of MRI Contrast Reagents. J. Am. Chem. Soc. 1999, 121,4278-4279.