The bimodal role of filamin in controlling the architecture and mechanics of F-actin networks.
Reconstituted actin filament networks have been used extensively to understand the mechanics of the actin cortex and decipher the role of actin cross-linking proteins in the maintenance and deformation of cell shape. However, studies of the mechanical role of the F-actin cross-linking protein filamin have led to seemingly contradictory conclusions, in part due to the use of ill-defined mechanical assays. Using quantitative rheological methods that avoid the pitfalls of previous studies, we systematically tested the complex mechanical response of reconstituted actin filament networks containing a wide range of filamin concentrations and compared the mechanical function of filamin with that of the cross-linking/bundling proteins alpha-actinin and fascin. At steady state and within a well defined linear regime of small non-destructive deformations, F-actin solutions behave as highly dynamic networks (actin polymers are still sufficiently mobile to relax the stress) below the cross-linking-to-bundling threshold filamin concentration, and they behave as covalently cross-linked gels above that threshold. Under large deformations, F-actin networks soften at low filamin concentrations and strain-harden at high filamin concentrations. Filamin cross-links F-actin into networks that are more resilient, stiffer, more solid-like, and less dynamic than alpha-actinin and fascin. These results resolve the controversy by showing that F-actin/filamin networks can adopt diametrically opposed rheological behaviors depending on the concentration in cross-linking proteins.
Department of Chemical and Biomolecular Engineering, The Johns Hopkins University, 3400 N. Charles Street, Baltimore, MD 21218, USA.
Yiider
Y
Tseng
Kwang M
KM
An
Osigwe
O
Esue
Denis
D
Wirtz
D000185:Actinin / Q000737:chemistry; D000199:Actins / Q000737:chemistry*; D000818:Animals; D002352:Carrier Proteins / Q000737:chemistry; D002645:Chickens; D003285:Contractile Proteins / Q000502:physiology*; D064448:Filamins; D005782:Gels; D008840:Microfilament Proteins / Q000737:chemistry / Q000502:physiology*
D000199:Actins; D002352:Carrier Proteins; D003285:Contractile Proteins; D064448:Filamins; D005782:Gels; D008840:Microfilament Proteins; D000185:Actinin; C020324:fascin