Metal ion dependency of microfibrils supports a rod-like conformation for fibrillin-1 calcium-binding epidermal growth factor-like domains

J Mol Biol. 1998 Mar 13;276(5):855-60. doi: 10.1006/jmbi.1997.1593.


The effects of the removal and replacement of divalent cations on the ultrastructure of 10 to 12 nm fibrillin-1-containing microfibrils have been studied, in order to investigate the conformation of fibrillin-1 calcium-binding epidermal growth factor-like (cbEGF-like) domains within the microfibril. The NMR structure of a covalently linked pair of cbEGF-like domains from fibrillin-1 recently identified a rigid rod-like conformation for the domain pair stabilised by interdomain calcium binding. This suggested that tandem arrays of fibrillin-1 cbEGF-like domains may adopt an extended conformation within a microfibril. If correct, then removal of bound calcium from fibrillin-1 would be expected to increase the flexibility of each cbEGF-like interdomain linkage, resulting in a decrease in the length of the interbead region of the microfibril (and thus a decrease in bead to bead periodicity), a concomitant increase in its diameter, and an overall increase in the flexibility of the microfibril. Our results show that removal of calcium by treatment with EGTA causes a large alteration of the microfibril structure, resulting in microfibrils with a reduced beaded periodicity, a disrupted interbead region and an increased overall flexibility. These effects are readily reversible by the re-addition of calcium (in the form of CaCl2), but not by the addition of magnesium (MgCl2). This is consistent with conformational changes in cbEGF-like domains causing the major structural effects on the microfibril. These results provide the first direct experimental evidence to support an extended rod-like conformation for multiple tandem repeats of fibrillin-1 cbEGF-like domains within the microfibril, as predicted by the NMR structure of an isolated fibrillin-1 cbEGF-like domain pair.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Actin Cytoskeleton / chemistry*
  • Actin Cytoskeleton / metabolism*
  • Actin Cytoskeleton / ultrastructure
  • Binding Sites
  • Calcium / metabolism
  • Cations, Divalent / metabolism
  • Cell Line
  • Chelating Agents
  • Edetic Acid
  • Egtazic Acid
  • Epidermal Growth Factor / metabolism
  • Fibrillin-1
  • Fibrillins
  • Humans
  • Magnetic Resonance Spectroscopy
  • Marfan Syndrome / metabolism
  • Microfilament Proteins / chemistry*
  • Microfilament Proteins / metabolism*
  • Microfilament Proteins / ultrastructure
  • Microscopy, Electron
  • Protein Conformation


  • Cations, Divalent
  • Chelating Agents
  • FBN1 protein, human
  • Fibrillin-1
  • Fibrillins
  • Microfilament Proteins
  • Egtazic Acid
  • Epidermal Growth Factor
  • Edetic Acid
  • Calcium