title: Biogenesis of extracellular microfibrils: Multimerization of the fibrillin-1 C terminus into bead-like structures enables self-assembly.
abstract: Microfibrils are essential elements in elastic and nonelastic tissues contributing to homeostasis and growth factor regulation. Fibrillins form the core of these multicomponent assemblies. Various human genetic disorders, the fibrillinopathies, arise from mutations in fibrillins and are frequently associated with aberrant microfibril assembly. These disorders include Marfan syndrome, Weill-Marchesani syndrome, Beals syndrome, and others. Although homotypic and heterotypic fibrillin self-interactions are considered to provide critical initial steps, the detailed mechanisms for microfibril assembly are unknown. We show here that the C-terminal recombinant half of fibrillin-1 assembles into disulfide-bonded multimeric globular structures with peripheral arms and a dense core. These globules are similar to the beaded structures observed in microfibrils isolated from tissues. Only these C-terminal fibrillin-1 multimers interacted strongly with the fibrillin-1 N terminus, whereas the monomers showed very little self-interaction activity. The multimers strongly inhibited microfibril formation in cell culture, providing evidence that these recombinant assemblies can also interact with endogenous fibrillin-1. The C-terminal self-interaction site was fine-mapped to the last three calcium-binding EGF domains in fibrillin-1. These results suggest a new mechanism for microfibril formation where fibrillin-1 first oligomerizes via its C terminus before the partially or fully assembled bead-like structures can further interact with other beads via the fibrillin-1 N termini.
authors.affiliation: Faculty of Medicine, Department of Anatomy and Cell Biology and Faculty of Dentistry, Division of Biomedical Sciences, McGill University, Montreal, QC, Canada.
authors.forename: Dirk
authors.initials: D
authors.lastname: Hubmacher
authors.forename: Ehab I
authors.initials: EI
authors.lastname: El-Hallous
authors.forename: Valentin
authors.initials: V
authors.lastname: Nelea
authors.forename: Mari T
authors.initials: MT
authors.lastname: Kaartinen
authors.forename: Eunice R
authors.initials: ER
authors.lastname: Lee
authors.forename: Dieter P
authors.initials: DP
authors.lastname: Reinhardt
mesh_terms: D002460:Cell Line; D004797:Enzyme-Linked Immunosorbent Assay; D005110:Extracellular Space / Q000378:metabolism*; D000071838:Fibrillin-1; D000071837:Fibrillins; D005347:Fibroblasts / Q000378:metabolism; D006801:Humans; D020894:Microfibrils / Q000737:chemistry / Q000378:metabolism*; D008840:Microfilament Proteins / Q000737:chemistry* / Q000378:metabolism* / Q000648:ultrastructure; D020836:Protein Structure, Quaternary; D011994:Recombinant Proteins / Q000378:metabolism; D017384:Sequence Deletion; D054392:Adipokines
chemical_list: D000071838:Fibrillin-1; D000071837:Fibrillins; D008840:Microfilament Proteins; D011994:Recombinant Proteins; C000605722:FBN1 protein, human; D054392:Adipokines