ABSTRACT Fibrillin rich microfibrils are ubiquitous components of most connective tissues in all animal phyla. Tissue such as dermis, blood vessels or ciliary zonules of the eye all require elasticity as a fundamental component of their physiological function and are particularly rich in microfibrils [1, 2]. The ultrastructure of fibrillin-rich microfibrils is rather complex due to their non-crystalline, variable, heterogeneous nature, and a universal model concordant with all methods and tissues studied has yet to be found. Structural studies using techniques such as small-angle X-ray scattering or rotary-shadowing electron microscopic techniques indicate that fibrillin assemblies present structural organisation at a number of hierarchical levels from molecular packing through suprafibrillar assemblies to bundles and thence a functional tissue [3-8]. Baldock et al. [9] have proposed a model of supramolecular arrangement of fibrillin-rich microfibrils, based on three-dimensional tomographic reconstructions and antibody epitope mapping. This model has been recently challenged by Lee et al. [10], who have suggested a simpler model of fibrillin alignment into microfibrils, deduced from the crystal structure of the integrin-fibrillin complex. These various possible models of fibrillin packing indicate that there is still much to be understood in the physicochemical relationship of fibrillin- rich tissues. Elastin, fibrillin-1 and fibrillin-2 clearly have different physiological functions as proven by the different phenotypes caused by the respective protein mutations. A current major challenge is to determine the structural organisation of microfibrils when constituted by each fibrillin-type, with or without elastin, in normal tissue. This would link structural changes with each mutation of the protein associated with genetic diseases such as Marfan’s syndrome.
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