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Glycosaminoglycan; Chemokine; T-lymphocyte adhesion; Quartz crystal microbalance; Spectroscopic ellipsometry; Surface plasmon resonance
Abstract:
Glycosaminoglycans (GAGs) are ubiquitously present at the cell surface and in extracellular matrix, and crucial for matrix assembly, cell-cell and cell-matrix interactions. The supramolecular presentation of GAG chains, along with other matrix components, is likely to be functionally important but remains challenging to control and to characterize, both in vivo and in vitro. We present a method to create well-defined biomimetic surfaces that display GAGs, either alone or together with other cell ligands, in a background that suppresses non-specific binding. Through the design of the immobilization platform a streptavidin monolayer serves as a molecular breadboard for the attachment of various biotinylated ligands and a set of surface-sensitive in situ analysis techniques (including quartz crystal microbalance and spectroscopic ellipsometry), the biomimetic surfaces are tailor made with tight control on biomolecular orientation, surface density and lateral mobility. Analysing the interactions between a selected GAG (heparan sulphate, HS) and the HS-binding chemokine CXCL12 alpha (also called SDF-1 alpha), we demonstrate that these surfaces are versatile for biomolecular and cellular interaction studies. T-lymphocytes are found to adhere specifically to surfaces presenting CXCL12 alpha, both when reversibly bound through HS and when irreversibly immobilized on the inert surface, even in the absence of any bona fide cell adhesion ligand. Moreover, surfaces which present both HS-bound CXCL12 alpha and the intercellular adhesion molecule 1 (ICAM-1) synergistically promote cell adhesion. Our surface biofunctionalization strategy should be broadly applicable for functional studies that require a well-defined supramolecular presentation of GAGs along with other matrix or cell-surface components.
