Dynamic cross-linking by alpha-actinin determines the mechanical properties of actin filament networks.
We used smooth muscle alpha-actinin to evaluate the contribution of cross-linker dynamics to the mechanical properties of actin filament networks. Recombinant actin-binding domain (residues 2-269) binds actin filaments with a Kd of 1 microM at 25 degrees C, 20 times stronger than actin-binding domain produced by thermolysin digestion of native alpha-actinin (residues 25-257). Between 8 and 25 degrees C the rate constants for recombinant actin-binding domain to bind to (0.8-2.7 microM-1 s-1) and dissociate from (0.2-2.4 s-1) actin filaments depend on temperature. At 8 degrees C actin filaments cross-linked with alpha-actinin are stiff and nearly solid, whereas at 25 degrees C the mechanical properties approach those of actin filaments alone. In these experiments, high actin concentrations kept most of the alpha-actinin bound to actin and temperature varied a single parameter, cross-linker dynamics, because the mechanical properties of pure actin filaments (a viscoelastic gel) or biotinylated actin filaments cross-linked irreversibly by avidin (a stiff viscoelastic solid) depend little on temperature. These results show that the rate of exchange of dynamic cross-links between actin filaments is an important determinant of the mechanical properties of the networks.
Xu
J
J
Department of Biophysics and Biophysical Chemistry, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA.
Wirtz
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Pollard
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TD
D000185:Actinin / Q000737:chemistry* / Q000378:metabolism*; D000199:Actins / Q000737:chemistry / Q000378:metabolism*; D000818:Animals; D001665:Binding Sites; D002645:Chickens; D003432:Cross-Linking Reagents; D004548:Elasticity; D007700:Kinetics; D008840:Microfilament Proteins / Q000737:chemistry / Q000378:metabolism*; D018482:Muscle, Skeletal / Q000378:metabolism; D009130:Muscle, Smooth / Q000378:metabolism; D011817:Rabbits; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D013816:Thermodynamics; D013820:Thermolysin; D014783:Viscosity
D000199:Actins; D003432:Cross-Linking Reagents; D008840:Microfilament Proteins; D011994:Recombinant Proteins; D000185:Actinin; D013820:Thermolysin