title: Spectroscopic study of conformational changes in subdomain 1 of G-actin: influence of divalent cations.
abstract: 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 degrees C. The width of the lifetime distribution is smaller by 30% in Mg-saturated actin monomer at 5 degrees C, and the difference becomes negligible above 30 degrees 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.
authors.affiliation: Department of Biophysics, University Medical School, Pécs, Hungary.
authors.forename: M
authors.initials: M
authors.lastname: Nyitrai
authors.forename: G
authors.initials: G
authors.lastname: Hild
authors.forename: J
authors.initials: J
authors.lastname: Belágyi
authors.forename: B
authors.initials: B
authors.lastname: Somogyi
mesh_terms: D000199:Actins / Q000737:chemistry* / Q000187:drug effects; D000818:Animals; D055592:Biophysical Phenomena; D001703:Biophysics; D002118:Calcium / Q000494:pharmacology; D002413:Cations, Divalent; D004578:Electron Spin Resonance Spectroscopy; D005454:Fluorescence Polarization; D005456:Fluorescent Dyes; D066298:In Vitro Techniques; D008274:Magnesium / Q000494:pharmacology; D009282:Naphthalenesulfonates; D011487:Protein Conformation / Q000187:drug effects; D011817:Rabbits; D013050:Spectrometry, Fluorescence; D013696:Temperature
chemical_list: D000199:Actins; D002413:Cations, Divalent; D005456:Fluorescent Dyes; D009282:Naphthalenesulfonates; C006421:1,5-I-AEDANS; D008274:Magnesium; D002118:Calcium