Direct detection of the binding of avidin and lactoferrin fluorescent probes to heparinized surfaces

Fibulin-3, -4, and -5 are highly susceptible to proteolysis, interact with cells and heparin, and form multimers

Extracellular short fibulins, fibulin-3, -4, and -5, are components of the elastic fiber/microfibril system and are implicated in the formation and homeostasis of elastic tissues. In this study, we report new structural and functional properties of the short fibulins. Full-length human short fibulins were recombinantly expressed in human embryonic kidney cells and purified by immobilized metal ion affinity chromatography. All three fibulins showed various levels of degradation after the purification procedure. N-terminal sequencing revealed that all three fibulins are highly susceptible to proteolysis within the N-terminal linker region of the first calcium-binding epidermal growth factor domain. Proteolytic susceptibility of the linker correlated with its length. Exposure of these fibulins to matrix metalloproteinase (MMP)-1, -2, -3, -7, -9, and -12 resulted in similar proteolytic fragments with MMP-7 and -12 being the most potent proteases. Fibulin-3 proteolysis was almost completely inhibited in cell culture by the addition of 25 μm doxycycline (a broad spectrum MMP inhibitor). Reducible fibulin-4 dimerization and multimerization were consistently observed by SDS-PAGE, Western blotting, and mass spectrometry. Atomic force microscopy identified monomers, dimers, and multimers in purified fibulin-4 preparations with sizes of ∼10-15, ∼20-25, and ∼30-50 nm, respectively. All short fibulins strongly adhered to human fibroblasts and smooth muscle cells. Although only fibulin-5 has an RGD integrin binding site, all short fibulins adhere at a similar level to the respective cells. Solid phase binding assays detected strong calcium-dependent binding of the short fibulins to immobilized heparin, suggesting that these fibulins may bind cell surface-located heparan sulfate.

Quantitation of surface-reducing-end covalently bound polysaccharides via hydrazinolysis and deamination

Depending on the method of deposition, reactive sites of polysaccharides on substrates may not be available when their reducing ends have been used to covalently bind them to the substrates. Here we present a method that allows surface density measurements of reducing-end covalently bound polysaccharides in a procedure that cleaves the polysaccharide chain from the surface via hydrazinolysis and deamination, leaving on the surface a disaccharide that is later radiolabeled with an aldehyde in a reaction with enamine formation. The method described has the advantage that it may be used with any polysaccharide patterned to any surface exposing an amino-terminated monolayer by reductive amination of their galactosamine or glucosamine repeating units. We illustrate the technique with the quantitation of glycosaminoglycans (GAGs) on silanized glass surfaces.