title: Nanostructure of fibrillin-1 reveals compact conformation of EGF arrays and mechanism for extensibility.
abstract: Fibrillin-1 is a 330-kDa multidomain extracellular matrix protein that polymerizes to form 57-nm periodic microfibrils, which are essential for all tissue elasticity. Fibrillin-1 is a member of the calcium-binding EGF repeat family and has served as a prototype for structural analyses. Nevertheless, both the detailed structure of fibrillin-1 and its organization within microfibrils are poorly understood because of the complexity of the molecule and the resistance of EGF arrays to crystallization. Here, we have used small-angle x-ray scattering and light scattering to analyze the solution structure of human fibrillin-1 and to produce ab initio structures of overlapping fragments covering 90% of the molecule. Rather than exhibiting a uniform rod shape as current models predict, the scattering data revealed a nonlinear conformation of calcium-binding EGF arrays in solution. This finding has major implications for the structures of the many other EGF-containing extracellular matrix and membrane proteins. The scattering data also highlighted a very compact, globular region of the fibrillin-1 molecule, which contains the integrin and heparan sulfate-binding sites. This finding was confirmed by calculating a 3D reconstruction of this region using electron microscopy and single-particle image analysis. Together, these data have enabled the generation of an improved model for microfibril organization and a previously undescribed mechanism for microfibril extensibility.
authors.affiliation: Wellcome Trust Centre for Cell-Matrix Research, Faculty of Life Sciences, Michael Smith Building, University of Manchester, Greater Manchester M13 9PT, UK. clair.baldock@manchester.ac.uk
authors.forename: Clair
authors.initials: C
authors.lastname: Baldock
authors.forename: Veronique
authors.initials: V
authors.lastname: Siegler
authors.forename: Daniel V
authors.initials: DV
authors.lastname: Bax
authors.forename: Stuart A
authors.initials: SA
authors.lastname: Cain
authors.forename: Kieran T
authors.initials: KT
authors.lastname: Mellody
authors.forename: Andrew
authors.initials: A
authors.lastname: Marson
authors.forename: J Louise
authors.initials: JL
authors.lastname: Haston
authors.forename: Richard
authors.initials: R
authors.lastname: Berry
authors.forename: Ming-Chuan
authors.initials: MC
authors.lastname: Wang
authors.forename: J Günter
authors.initials: JG
authors.lastname: Grossmann
authors.forename: Manfred
authors.initials: M
authors.lastname: Roessle
authors.forename: Cay M
authors.initials: CM
authors.lastname: Kielty
authors.forename: Tim J
authors.initials: TJ
authors.lastname: Wess
mesh_terms: D004815:Epidermal Growth Factor / Q000737:chemistry; D005109:Extracellular Matrix / Q000378:metabolism; D000071838:Fibrillin-1; D000071837:Fibrillins; D006497:Heparan Sulfate / Q000737:chemistry; D006801:Humans; D007091:Image Processing, Computer-Assisted; D007700:Kinetics; D008840:Microfilament Proteins / Q000737:chemistry*; D008854:Microscopy, Electron; D008956:Models, Chemical; D008958:Models, Molecular; D008968:Molecular Conformation; D049329:Nanostructures; D017434:Protein Structure, Tertiary; D054392:Adipokines
chemical_list: D004815:Epidermal Growth Factor; D000071838:Fibrillin-1; D000071837:Fibrillins; D006497:Heparan Sulfate; D008840:Microfilament Proteins; C000605722:FBN1 protein, human; D054392:Adipokines