Calcium Determines the Supramolecular Organization of Fibrillin-Rich Microfibrils

• Published in: The Journal of cell biology Vol. 141; no. 3; pp. 829 - 837
• Main Authors: Wess, T. J., Purslow, P. P., Sherratt, M. J., Ashworth, J., Shuttleworth, C. A., Kielty, C. M.
• Format: Journal Article
• Language: English
• Published: United States Rockefeller University Press 04-05-1998; The Rockefeller University Press
• Subjects: Animals; Average linear density; Biopolymers; Calcium; Calcium - metabolism; Cattle; Cellular biology; Ciliary Body - chemistry; Ciliary Body - metabolism; Ciliary Body - ultrastructure; Computer Simulation; Elastic tissue; Extracellular Matrix - ultrastructure; Extracellular Matrix Proteins - chemistry; Extracellular Matrix Proteins - metabolism; Extracellular Matrix Proteins - ultrastructure; Eyes & eyesight; Fibrillins; Mass distribution; Microfilament Proteins - chemistry; Microfilament Proteins - metabolism; Microfilament Proteins - ultrastructure; Models, Molecular; Periodicity; Solar fibrils; Transmission electron microscopy; Ungulates; Wave diffraction; X ray diffraction
• ISSN: 0021-9525; 1540-8140
• DOI: 10.1083/jcb.141.3.829

Microfibrils are ubiquitous fibrillin-rich polymers that are thought to provide long-range elasticity to extracellular matrices, including the zonular filaments of mammalian eyes. X-ray diffraction of hydrated bovine zonular filaments demonstrated meridional diffraction peaks indexing on a fundamental axial periodicity (D) of ∼56 nm. A Ca2+-induced reversible change in the intensities of the meridional Bragg peaks indicated that supramolecular rearrangements occurred in response to altered concentrations of free Ca2+. In the presence of Ca2+, the dominant diffracting subspecies were microfibrils aligned in an axial 0.33-D stagger. The removal of Ca2+ caused an enhanced regularity in molecular spacing of individual microfibrils, and the contribution from microfibrils not involved in staggered arrays became more dominant. Scanning transmission electron microscopy of isolated microfibrils revealed that Ca2+ removal or addition caused significant, reversible changes in microfibril mass distribution and periodicity. These results were consistent with evidence from x-ray diffraction. Simulated meridional x-ray diffraction profiles and analyses of isolated Ca2+-containing, staggered microfibrillar arrays were used to interpret the effects of Ca2+. These observations highlight the importance of Ca2+ to microfibrils and microfibrillar arrays in vivo.