title: The influence of divalent cations on the dynamic properties of actin filaments: a spectroscopic study.
abstract: The principal aim of this investigation was to study the change of the protein flexibility and/or conformational properties of actin filaments upon the replacement of Ca2+ by Mg2+. The temperature dependence of the fluorescence lifetime and the anisotropy decay of N-(iodoacetyl)-N'-(5-sulfo-1-naphthyl)ethylenediamine (IAEDANS) attached covalently to the Cys374 residue of actin were measured. Saturation transfer electron paramagnetic resonance (ST-EPR) experiments were also carried out using N-(1-oxyl-2,2,6, 6-tetramethyl-4-piperidinyl)-maleimide (MSL) attached to the same residue (Cys374). The Arrhenius analysis of the temperature dependence of the fluorescence lifetimes shows that for Mg-F-actin, both the activation energy (E*) and the frequency factor (A) are smaller than they are for Ca-F-actin. The longer rotational correlation times resolved in the fluorescence experiments are larger in the Mg2+-loaded form of the actin filament between 6 degreesC and 28 degreesC, but this difference becomes negligible above 28 degreesC. The results of saturation transfer electron paramagnetic resonance measurements on maleimide spin-labeled actin filaments indicate that the replacement of Ca2+ by Mg2+ induced a decrease of the mobility of the label on the sub-millisecond time scale. Based upon these results, we concluded that the filaments polymerized from Ca-actin are more flexible than the filaments of Mg-actin.
authors.affiliation: Department of Biophysics, University Medical School of Pécs, P.O.B. 99. H-7601 Pécs, Hungary.
authors.forename: G
authors.initials: G
authors.lastname: Hild
authors.forename: M
authors.initials: M
authors.lastname: Nyitrai
authors.forename: J
authors.initials: J
authors.lastname: Belágyi
authors.forename: B
authors.initials: B
authors.lastname: Somogyi
mesh_terms: D000199:Actins / Q000737:chemistry* / Q000502:physiology*; D000818:Animals; D055592:Biophysical Phenomena; D001703:Biophysics; D002118:Calcium / Q000737:chemistry; D002413:Cations, Divalent / Q000737:chemistry; D004578:Electron Spin Resonance Spectroscopy; D005454:Fluorescence Polarization; D005456:Fluorescent Dyes; D066298:In Vitro Techniques; D008027:Light; D008274:Magnesium / Q000737:chemistry; D009119:Muscle Contraction / Q000502:physiology; D009282:Naphthalenesulfonates; D011487:Protein Conformation; D011817:Rabbits; D012542:Scattering, Radiation; D013113:Spin Labels; D013816:Thermodynamics
chemical_list: D000199:Actins; D002413:Cations, Divalent; D005456:Fluorescent Dyes; D009282:Naphthalenesulfonates; D013113:Spin Labels; C006421:1,5-I-AEDANS; D008274:Magnesium; D002118:Calcium