Fibrillin-1 Interactions with Heparin: Implications for Microfibril and Elastic Fibre Assembly *

Fibrillin-1 assembly into microfibrils and elastic fiber formation involve interactions with glycosaminoglycans. We have used BIAcore technology to investigate fibrillin-1 interactions with heparin, and with heparin saccharides that are analogous to S-domains of heparan sulfate. We have identified four high affinity heparin binding sites on fibrillin-1, localized three of these sites, and defined their binding kinetics. Heparin binding to the fibrillin-1 N-terminus has particularly rapid kinetics. Hyaluronan and chondroitin sulphate did not interact significantly with fibrillin-1. Heparin saccharides with more than twelve monosaccharide units bound strongly to all four fibrillin-1 sites. Heparin did not inhibit fibrillin-1 Nand Cterminal interactions, or RGD-dependent cell attachment, but heparin and MAGP-1 competed for binding to the fibrillin-1 N-terminus, and heparin and tropoelastin competed for binding to a central fibrillin-1 sequence. By regulating these key interactions, heparin can profoundly influence microfibril and elastic fibre assembly. Elastic fibers are insoluble extracellular assemblies in elastic tissues such as aorta, lung and skin (1,2). Their major role is to endow vascular and other dynamic connective tissues with elasticity and resilience. They morphologically comprise an elastin core and an outer mantle of fibrillin-rich microfibrils. During elastic fiber formation, tropoelastin is deposited on preformed microfibrillar templates. Deposits of elastin first appear within microfibril bundles and gradually coalesce, whilst microfibrils are gradually displaced to the periphery or subsumed into the elastin core.