The binding of terbium ions to tubulin induces ring formation

Arch Biochem Biophys. 1993 Feb 1;300(2):582-7. doi: 10.1006/abbi.1993.1081.

Abstract

The intrinsic fluorescence excitation and emission spectra of chicken brain tubulin showed the characteristic tryptophan fluorescence. The emission spectrum of Tb3+ in the presence of tubulin and GTP excited at 295 nm, showed four peaks, with the maxima at 490, 545, and 586 nm and a minor peak around 620 nm. Titration of tubulin with Tb3+ was followed by the increment in luminescence at 545 nm and showed a sigmoidal curve where the initial lag interval and the maximal luminescence intensity depended on tubulin concentration. The presence of Mg2+, Co2+, and Zn2+ diminished both the sigmoidicity of the curve and the maximal luminescence intensity. Titration of tubulin with Tb3+ also produced a sigmoidal increase in turbidity, which was shifted to the left with respect to the luminescence curve. The dependence of turbidity on the wavelength of the Tb(3+)-induced polymers revealed that the large structures formed were not microtubules. Electron microscopy of the aggregates induced by Tb3+ showed mainly a lattice of double rings with side-by-side contacts. These results indicate that Tb3+ induces principally double ring formation and that these rings (33 +/- 2 nm external diameter) aggregate in large-ordered arrays. The luminescence of Tb3+ seems to be induced mainly by the aggregation of rings.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Brain / metabolism
  • Chickens
  • Chlorides / pharmacology
  • Cobalt / pharmacology
  • Kinetics
  • Macromolecular Substances
  • Magnesium / pharmacology
  • Manganese / pharmacology
  • Manganese Compounds*
  • Microscopy, Electron
  • Protein Binding
  • Protein Conformation*
  • Spectrometry, Fluorescence
  • Terbium / chemistry
  • Terbium / metabolism*
  • Tubulin / chemistry
  • Tubulin / metabolism*
  • Tubulin / ultrastructure
  • Zinc / pharmacology
  • Zinc Compounds*

Substances

  • Chlorides
  • Macromolecular Substances
  • Manganese Compounds
  • Tubulin
  • Zinc Compounds
  • Terbium
  • Cobalt
  • Manganese
  • zinc chloride
  • cobaltous chloride
  • Magnesium
  • Zinc
  • manganese chloride