Fibrillin-1: organization in microfibrils and structural properties.

To investigate the microfibrillar organization and structural properties of fibrillin-1, we produced overlapping recombinant peptides in human cells which altogether span the fibrillin-1 molecule. The peptides were purified under non-denaturing conditions and extensive characterization indicated correct folding. The purified proteins were used to map monoclonal antibodies 26, 69 and 201. The binding sites are located at the N-terminal end between amino acid residues 45 and 450 (mAb 26), 451 and 909 (mAb 201) and at the C-terminal end between residues 2093 and 2871 (mAb 69). Immunolocalization of these antibodies to extended beaded structures (microfibrils) demonstrated that the N- and C-terminal ends of fibrillin-1 are located in proximity and on opposite sides of the beads, and more central parts of the molecule are located between the beads. Each epitope is present once between each bead. These data allow two possible models for the organization of fibrillin in microfibrils. However, comparison of distances between antibody binding sites on the recombinant peptides and labeling events in tissue suggests that fibrillin molecules are compacted within their tissue form as microfibrils. Additional analysis of the recombinant peptides provide new information regarding the eight-cysteine motif, a novel domain present in fibrillins and TGF beta binding proteins, and suggest that fibrillins are processed at their N-and C-terminal ends.