Spectroscopic study of conformational changes in subdomain 1 of G- actin: Influence of divalent cations

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Temperature dependence of the fluorescence intensity and anisotropy decay of N~(Iodoacetyl)-N'-(5-sulfo-1-naphthyl)ethylenediamine attached to Cys374 of actin monomer was investigated to characterize conformational differences between Ca- and Mg-G-actin. The fluorescence lifetime is longer in Mg-G-actin than that in Ca-G-actin in the temperature range of 5-34°C. The width of the lifetime distribution is smaller by 30% in Mg-saturated actin monomer at 5°C, and the difference becomes negligible above 30°C. The semiangle of the cone within which the fluorophore can rotate is larger in Ca-G-actin at all temperatures. Electron paramagnetic resonance measurements on maleimide spin-labeled (on Cys374) monomer actin gave evidence that exchange of Ca2+ for Mg2+ induced a rapid decrease in the mobility of the label immediately after the addition of Mg2+. These results suggest that the C-terminal region of the monomer becomes more rigid as a result of the replacement of Ca2+ by Mg2+. The change can be related to the difference between the polymerization abilities of the two forms of G-actin.

Original languageEnglish
Pages (from-to)2023-2032
Number of pages10
JournalBiophysical journal
Issue number4
Publication statusPublished - Oct 1997

ASJC Scopus subject areas

  • Biophysics

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