NUCLEOTIDES INCREASE THE INTERNAL FLEXIBILITY OF FILAMENTS OF DEPHOSPHORYLATED ACANTHAMOEBA MYOSIN-II

Citation
Mj. Redowicz et al., NUCLEOTIDES INCREASE THE INTERNAL FLEXIBILITY OF FILAMENTS OF DEPHOSPHORYLATED ACANTHAMOEBA MYOSIN-II, The Journal of biological chemistry, 271(21), 1996, pp. 12401-12407
Citations number
40
Categorie Soggetti
Biology
ISSN journal
00219258
Volume
271
Issue
21
Year of publication
1996
Pages
12401 - 12407
Database
ISI
SICI code
0021-9258(1996)271:21<12401:NITIFO>2.0.ZU;2-2
Abstract
The actin-activated Mg2+-ATPase activity of Acanthamoeba myosin II min ifilaments is dependent both on Mg2+ concentration and on the state of phosphorylation of three serine sites at the C-terminal end of the he avy chains. Previous electric birefringence experiments on minifilamen ts showed a large dependence of signal amplitude on the phosphorylatio n state and Mg2+ concentration, consistent with large changes in filam ent flexibility. These observations suggested that minifilament stiffn ess was important for function. We now report that the binding of nucl eotides to dephosphorylated minifilaments at Mg2+ concentrations neede d for optimal activity increases the flexibility by about 10-fold, as inferred from the birefringence signal amplitude increase. An increase in flexibility with nucleotide binding is not observed for dephosphor ylated minifilaments at lower Mg2+ concentrations or for phosphorylate d minifilaments at any Mg2+ concentration examined. The relaxation tim es for minifilament rotations that are sensitive to the conformation m yosin heads are also observed to depend on phosphorylation, Mg2+ conce ntration, and nucleotide binding. These latter experiments indicate th at the actin activated Mg2+-ATPase activity of Acanthamoeba myosin II correlates with both changes in myosin head conformation and the abili ty of minifilaments to cycle between stiff and flexible conformations coupled to nucleotide binding and release.