Department of Anatomy and Structural Biology
Albert Einstein College of Medicine
April 1, 2014
Tracking surface glycans on live cancer cells with single molecule sensitivity
A considerable body of literature describes the diffusive and anomalous dynamics of proteins and lipids in the plasma membrane of living cells, but less is known about the dynamics of cell-surface glycans. We exploit a combination of bioorthogonal click chemistry and single molecule tracking to investigate the dynamics of N-linked sialic acid and O-linked GalNAc in live cells metabolically labeled with azide- or alkyne-containing monosaccharide precursors. By optimizing the conditions of fluorescent tagging, mediated by Cu(I)-catalyzed azide-alkyne cycloaddition, and controlled bleaching, a sufficiently low spatial density of fluorescently-labeled glycan molecules is achieved, enabling dynamic single-molecule tracking. Unprecedented spatial and temporal resolution of the movement of surface glycans has allowed us to characterize the variation of the mean square displacement and cumulative distribution function for N-linked sialic acid and O-linked glycans with a cell's metastatic potential. We interpret the observed anomalous diffusion as arising from damped Brownian motion under a confining harmonic potential rather than caused by transient immobilization due to spatial inhomogeneities on the plasma membrane.