Differential dynamic behavior of actin filaments containing tightly- bound Ca2+ or Mg2+ in the presence of myosin heads actively hydrolyzing ATP

Conrad A. Rebello, Richard D. Ludescher

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Abstract

We have investigated how Ca2+ or Mg2+ bound at the high-affinity cation binding site ir F-actin modulates the dynamic response of these filaments to ATP hydrolysis by attached myosin head fragments (S1). Rotational motions of the filaments were monitored using steady-state phosphorescence emission anisotropy of the triplet probe erythrosin-5- iodoacetamide covalently attached to cysteine 374 of actin. The anisotropy of filaments containing only Ca2+ increased from 0.080 to 0.137 upon binding S1 in a rigor complex and decreased to 0.065 in the presence of ATP, indicating that S1 induced additional rotational motions in the filament during ATP hydrolysis. The comparable anisotropy values for Mg2+ containing filaments were 0.067, 0.137, and 0.065, indicating that S 1 hydrolysis did not induce measurable rotational motions in these filaments. Phalloidin, a fungal toxin which stabilizes F-actin and increases its rigidity, increased the anisotropy of F-actin containing either Ca2+ or Mg2+ but not the anisotropy of the 1:l S1-actin complexes of these filaments. Mg2+- containing filaments with phalloidin bound also displayed increased rotational motions during S1 ATP hydrolysis. A strong positive correlation between the phosphorescence anisotropy of F-actin under specific conditions and the extent of the rotational motions induced by S1 during ATP hydrolysis suggested that the long axis torsional rigidity of F-actin plays a crucial role in modulating the dynamic response of the filaments to ATP hydrolysis by S1. Cooperative responses of F-actin to dynamic perturbations induced by S1 during ATP hydrolysis may thus be physically mediated by the torsional rigidity of the filament.

Original languageEnglish (US)
Pages (from-to)13288-13295
Number of pages8
JournalBiochemistry
Volume38
Issue number40
DOIs
StatePublished - Oct 5 1999

All Science Journal Classification (ASJC) codes

  • Biochemistry

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