Conformation changes of actin during formation of filaments and paracrystals and upon interaction with DNase I, cytochalasin B, and phalloidin
Spin labels attached to rabbit muscle actin became more immobilized upon conversion of actin from the G state to the F state with 50 mM KCl. Titration of G-actin with MgCl/sub 2/ produced F-actin-like EPR spectra between 2 and 5 mM, and F-actin filaments by electron microscopy. Higher concentrations of MgCl/sub 2/ produced bundles of actin and eventually paracrystals, accompanied by further immobilization of spin labels. The effects of MgCl/sub 2/ and KCl were competitive: addition of MgCl/sub 2/ to 50 mM could convert F-actin (50 mM KCl) to paracrystalline (P) actin; the reverse titration (0 to 200 mM KCl in the presence of 20 mM MgCl/sub 2/) was less complete. Addition of DNase I to G- or F-actin gave the expected amorphous electron micrographic pattern, and the actin was not sedimentable at (400,000 x g x h). EPR showed that the actin was in the G conformation. Addition of DNase I to paracrystalline actin gave the F conformation (EPR) but the actin was G by electron microscopy. Phalloidin converted G-actin to F-actin, had no effect on F-actin, and converted P-actin to the F state by electron microscopy but maintained the P conformation by EPR. Cytochalasin B produced no effects observable by EPR or centrifugation but untwisted paracrystals into nets. Since actin retained its P conformation by EPR in two states which were morphologically not P, we conclude that the P state is a distinct conformation of the actin molecule and that actin filaments aggregate to form bundles (and eventually paracrystals) when actin monomers are able to enter the P conformation.
- Research Organization:
- Univ. of Rochester, NY
- OSTI ID:
- 5842179
- Journal Information:
- J. Biol. Chem.; (United States), Vol. 255:3
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ACTIN
STRUCTURAL CHEMICAL ANALYSIS
MUSCLES
MORPHOLOGY
BIOCHEMICAL REACTION KINETICS
ELECTRON MICROSCOPY
ELECTRON SPIN RESONANCE
MOLECULAR STRUCTURE
RABBITS
ANIMALS
KINETICS
MAGNETIC RESONANCE
MAMMALS
MICROSCOPY
ORGANIC COMPOUNDS
PROTEINS
REACTION KINETICS
RESONANCE
VERTEBRATES
550800* - Morphology
550200 - Biochemistry