Metabolic selection of glycosylation defects in human cells

Changes in glycosylation are often associated with disease progression, but the genetic and metabolic basis of these events is rarely understood in de tail at a molecular level. We describe a metabolism-based approach to the s election of mutants in glycoconjugate biosynthesis that provides insight in to regulatory mechanisms for oligosaccharide expression and metabolic flux. Unnatural intermediates are used to challenge a specific pathway, and cell surface expression of their metabolic products provides a readout of flux in that pathway and a basis for selecting genetic mutants. The approach was applied to the sialic acid metabolic pathway in human cells, yielding nove l mutants with phenotypes related to the inborn metabolic defect sialuria a nd metastatic tumor cells.