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.  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. , 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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