Interaction between heparan sulfate and the Roundabout receptor at the single-molecule level

Scanning probe microscopy methodologies have advanced to the point that in situ measurements of complex biological systems can be routinely measured at the single-molecule level¹, providing information on rare states that can be lost in standard ensemble measurements²and allowing highly specific detection of various proteins and polysaccharides^3,4. One such system that has attracted considerable attention is that of the cell signaling pathway Slit-Roundabout (Robo), which has been implicated in the development of the nervous and cardiac systems and in tumorigenesis⁵. The Slit-Robo complex is stabilized and regulated by heparan sulfate, a linear, structurally-heterogeneous polysaccharide expressed widely on mammalian cell membranes⁶. Thus, better understanding of heparan sulfates regulatory role could allow us to target therapies related to this pathway⁷. Using dynamic force spectroscopic methods⁸, this research shows that is possible to create a model system allowing for the measurement of single-molecule interactions between the heparan sulfate variant heparin and the Robo1 protein, elucidating the kinetics of the interaction using the entire polysaccharide and in ambient conditions.

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