Analysis of protein-heparin interactions using a portable SPR instrument

Optical biosensors such as those based on surface plasmon resonance (SPR) are a key analytical tool for understanding biomolecular interactions and function as well as the quantitative analysis of analytes in a wide variety of settings. The advent of portable SPR instruments enables analyses in the field. A critical step in method development is the passivation and functionalisation of the sensor surface. We describe the assembly of a surface of thiolated oleyl ethylene glycol/biotin oleyl ethylene glycol and its functionalisation with streptavidin and reducing end biotinylated heparin for a portable SPR instrument. Such surfaces can be batch prepared and stored. Two examples of the analysis of heparin-binding proteins are presented. The binding of fibroblast growth factor 2 and competition for the binding of a heparan sulfate sulfotransferase by a library of selectively modified heparins and suramin, which identify the selectivity of the enzyme for sulfated structures in the polysaccharide and demonstrate suramin as a competitor for the enzyme’s sugar acceptor site. Heparin functionalised surfaces should have a wide applicability, since this polysaccharide is a close structural analogue of the host cell surface polysaccharide, heparan sulfate, a receptor for many endogenous proteins and viruses.