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The supramolecular organization of fibrillin-rich microfibrils.

Baldock C, Koster AJ, Ziese U, Rock MJ, Sherratt MJ, Kadler KE, Shuttleworth CA, Kielty CM - J. Cell Biol. (2001)

Bottom Line: Mass mapping shows that, in solution, microfibrils with periodicities of <70 and >140 nm are stable, but periodicities of approximately 100 nm are rare.Microfibrils comprise two in-register filaments with a longitudinal symmetry axis, with eight fibrillin molecules in cross section.We present a model of fibrillin alignment that fits all the data and indicates that microfibril extensibility follows conformation-dependent maturation from an initial head-to-tail alignment to a stable approximately one-third staggered arrangement.

View Article: PubMed Central - PubMed

Affiliation: Wellcome Trust Centre for Cell-Matrix Research, Schools of Biological Sciences and Medicine, University of Manchester, Manchester, M13 9PT, United Kingdom. clair.baldock@man.ac.uk

ABSTRACT
We propose a new model for the alignment of fibrillin molecules within fibrillin microfibrils. Automated electron tomography was used to generate three-dimensional microfibril reconstructions to 18.6-A resolution, which revealed many new organizational details of untensioned microfibrils, including heart-shaped beads from which two arms emerge, and interbead diameter variation. Antibody epitope mapping of untensioned microfibrils revealed the juxtaposition of epitopes at the COOH terminus and near the proline-rich region, and of two internal epitopes that would be 42-nm apart in unfolded molecules, which infers intramolecular folding. Colloidal gold binds microfibrils in the absence of antibody. Comparison of colloidal gold and antibody binding sites in untensioned microfibrils and those extended in vitro, and immunofluorescence studies of fibrillin deposition in cell layers, indicate conformation changes and intramolecular folding. Mass mapping shows that, in solution, microfibrils with periodicities of <70 and >140 nm are stable, but periodicities of approximately 100 nm are rare. Microfibrils comprise two in-register filaments with a longitudinal symmetry axis, with eight fibrillin molecules in cross section. We present a model of fibrillin alignment that fits all the data and indicates that microfibril extensibility follows conformation-dependent maturation from an initial head-to-tail alignment to a stable approximately one-third staggered arrangement.

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A model of fibrillin alignment in microfibrils. Schematic diagram depicting the folding of fibrillin molecules in a beaded microfibril. (a) A single NH2- and COOH-terminal processed molecule and N-glycosylation sites are indicated. Antibody epitopes are colored on the molecule (red, 2502; blue/cyan, 11C1.3; purple, PF2; orange, 2499). (b) Alignment in 160-nm periodicity microfibrils with dashed circles representing regions of the molecule predicted to contribute to the bead. (c) Molecular folding that would generate ∼100-nm periodicity; solid black lines show the position of possible transglutaminase cross links and solid circles show the bead position. (d) Packing and folding that would generate the stable 56-nm periodicity microfibrils. The evidence for the model is presented in the Discussion. While the predicted folds are shown, it should be noted that the precise packing arrangement of folded segments contributing to the bead remains unresolved.
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Figure 5: A model of fibrillin alignment in microfibrils. Schematic diagram depicting the folding of fibrillin molecules in a beaded microfibril. (a) A single NH2- and COOH-terminal processed molecule and N-glycosylation sites are indicated. Antibody epitopes are colored on the molecule (red, 2502; blue/cyan, 11C1.3; purple, PF2; orange, 2499). (b) Alignment in 160-nm periodicity microfibrils with dashed circles representing regions of the molecule predicted to contribute to the bead. (c) Molecular folding that would generate ∼100-nm periodicity; solid black lines show the position of possible transglutaminase cross links and solid circles show the bead position. (d) Packing and folding that would generate the stable 56-nm periodicity microfibrils. The evidence for the model is presented in the Discussion. While the predicted folds are shown, it should be noted that the precise packing arrangement of folded segments contributing to the bead remains unresolved.

Mentions: We have derived a model of fibrillin alignment in microfibrils based on (a) AET-generated three-dimensional reconstructions of untensioned microfibrils that define microfibril dimensions and molecular organization, (b) mapping of antibody and colloidal gold binding sites in directionally orientated untensioned microfibrils, which demonstrate intramolecular folding, (c) mass changes on microfibril extension showing that interbead unfolding precedes bead unraveling, (d) immunofluorescence studies of extracellular fibrillin deposition that show a major conformational change, and (e) published observations (Keene et al. 1991; Downing et al. 1996; Reinhardt et al. 1996, Reinhardt et al. 1997; Qian and Glanville 1997; Sherratt et al. 1997, Sherratt et al. 2001; Yuan et al. 1997; Wess et al. 1998a; Ashworth et al. 1999a). Our model predicts maturation from a parallel head-to-tail alignment to an approximately one-third stagger that is stable as a 56-nm folded form, but not as an ∼100-nm form (Fig. 5). This model accounts for all microfibril structural features, suggests that inter- and intramolecular interactions drive conformation changes to form extensible microfibrils, and defines the number of molecules in cross section.


The supramolecular organization of fibrillin-rich microfibrils.

Baldock C, Koster AJ, Ziese U, Rock MJ, Sherratt MJ, Kadler KE, Shuttleworth CA, Kielty CM - J. Cell Biol. (2001)

A model of fibrillin alignment in microfibrils. Schematic diagram depicting the folding of fibrillin molecules in a beaded microfibril. (a) A single NH2- and COOH-terminal processed molecule and N-glycosylation sites are indicated. Antibody epitopes are colored on the molecule (red, 2502; blue/cyan, 11C1.3; purple, PF2; orange, 2499). (b) Alignment in 160-nm periodicity microfibrils with dashed circles representing regions of the molecule predicted to contribute to the bead. (c) Molecular folding that would generate ∼100-nm periodicity; solid black lines show the position of possible transglutaminase cross links and solid circles show the bead position. (d) Packing and folding that would generate the stable 56-nm periodicity microfibrils. The evidence for the model is presented in the Discussion. While the predicted folds are shown, it should be noted that the precise packing arrangement of folded segments contributing to the bead remains unresolved.
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Related In: Results  -  Collection

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Figure 5: A model of fibrillin alignment in microfibrils. Schematic diagram depicting the folding of fibrillin molecules in a beaded microfibril. (a) A single NH2- and COOH-terminal processed molecule and N-glycosylation sites are indicated. Antibody epitopes are colored on the molecule (red, 2502; blue/cyan, 11C1.3; purple, PF2; orange, 2499). (b) Alignment in 160-nm periodicity microfibrils with dashed circles representing regions of the molecule predicted to contribute to the bead. (c) Molecular folding that would generate ∼100-nm periodicity; solid black lines show the position of possible transglutaminase cross links and solid circles show the bead position. (d) Packing and folding that would generate the stable 56-nm periodicity microfibrils. The evidence for the model is presented in the Discussion. While the predicted folds are shown, it should be noted that the precise packing arrangement of folded segments contributing to the bead remains unresolved.
Mentions: We have derived a model of fibrillin alignment in microfibrils based on (a) AET-generated three-dimensional reconstructions of untensioned microfibrils that define microfibril dimensions and molecular organization, (b) mapping of antibody and colloidal gold binding sites in directionally orientated untensioned microfibrils, which demonstrate intramolecular folding, (c) mass changes on microfibril extension showing that interbead unfolding precedes bead unraveling, (d) immunofluorescence studies of extracellular fibrillin deposition that show a major conformational change, and (e) published observations (Keene et al. 1991; Downing et al. 1996; Reinhardt et al. 1996, Reinhardt et al. 1997; Qian and Glanville 1997; Sherratt et al. 1997, Sherratt et al. 2001; Yuan et al. 1997; Wess et al. 1998a; Ashworth et al. 1999a). Our model predicts maturation from a parallel head-to-tail alignment to an approximately one-third stagger that is stable as a 56-nm folded form, but not as an ∼100-nm form (Fig. 5). This model accounts for all microfibril structural features, suggests that inter- and intramolecular interactions drive conformation changes to form extensible microfibrils, and defines the number of molecules in cross section.

Bottom Line: Mass mapping shows that, in solution, microfibrils with periodicities of <70 and >140 nm are stable, but periodicities of approximately 100 nm are rare.Microfibrils comprise two in-register filaments with a longitudinal symmetry axis, with eight fibrillin molecules in cross section.We present a model of fibrillin alignment that fits all the data and indicates that microfibril extensibility follows conformation-dependent maturation from an initial head-to-tail alignment to a stable approximately one-third staggered arrangement.

View Article: PubMed Central - PubMed

Affiliation: Wellcome Trust Centre for Cell-Matrix Research, Schools of Biological Sciences and Medicine, University of Manchester, Manchester, M13 9PT, United Kingdom. clair.baldock@man.ac.uk

ABSTRACT
We propose a new model for the alignment of fibrillin molecules within fibrillin microfibrils. Automated electron tomography was used to generate three-dimensional microfibril reconstructions to 18.6-A resolution, which revealed many new organizational details of untensioned microfibrils, including heart-shaped beads from which two arms emerge, and interbead diameter variation. Antibody epitope mapping of untensioned microfibrils revealed the juxtaposition of epitopes at the COOH terminus and near the proline-rich region, and of two internal epitopes that would be 42-nm apart in unfolded molecules, which infers intramolecular folding. Colloidal gold binds microfibrils in the absence of antibody. Comparison of colloidal gold and antibody binding sites in untensioned microfibrils and those extended in vitro, and immunofluorescence studies of fibrillin deposition in cell layers, indicate conformation changes and intramolecular folding. Mass mapping shows that, in solution, microfibrils with periodicities of <70 and >140 nm are stable, but periodicities of approximately 100 nm are rare. Microfibrils comprise two in-register filaments with a longitudinal symmetry axis, with eight fibrillin molecules in cross section. We present a model of fibrillin alignment that fits all the data and indicates that microfibril extensibility follows conformation-dependent maturation from an initial head-to-tail alignment to a stable approximately one-third staggered arrangement.

Show MeSH
Related in: MedlinePlus