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Biophys J. 2008 Nov 15;95(10):4915-23. doi: 10.1529/biophysj.108.131722. Epub 2008 Aug 8.

Dynamic viscoelasticity of actin cross-linked with wild-type and disease-causing mutant alpha-actinin-4.

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  • 1Department of Physics and School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, USA.


The actin cross-linker alpha-actinin-4 has been found to be indispensable for the structural and functional integrity of podocytes; deficiency or alteration of this protein due to mutations results in kidney disease. To gain insight into the effect of the cross-linker on cytoskeletal mechanics, we studied the macroscopic rheological properties of actin networks cross-linked with wild-type and mutant alpha-actinin-4. The frequency-dependent viscoelasticity of the networks is characterized by an elastic plateau at intermediate frequencies, and relaxation toward fluid properties at low frequencies. The relaxation frequencies of networks with mutant alpha-actinin-4 are an order of magnitude lower than that with the wild-type, suggesting a slower reaction rate for the dissociation of actin and alpha-actinin for the mutant, consistent with a smaller observed equilibrium dissociation constant. This difference can be attributed to an additional binding site that is exposed as a result of the mutation, and can be interpreted as a difference in binding energy barriers. This is further supported by the Arrhenius-like temperature dependence of the relaxation frequencies.

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