Cryoelectron microscopy was used to obtain a 3-D image at 2.0 nm resolution of 2-D arrays of smooth muscle alpha-actinin. The reconstruction reveals a well-resolved long central domain with 90 degrees of left-handed twist and near 2-fold symmetry. However, the molecular ends which contain the actin binding and calmodulin-like domains, have different structures oriented approximately 90 degrees to each other ...
Cryoelectron microscopy was used to obtain a 3-D image at 2.0 nm resolution of 2-D arrays of smooth muscle alpha-actinin. The reconstruction reveals a well-resolved long central domain with 90 degrees of left-handed twist and near 2-fold symmetry. However, the molecular ends which contain the actin binding and calmodulin-like domains, have different structures oriented approximately 90 degrees to each other. Atomic structures for the alpha-actinin domains were built by homology modeling and assembled into an atomic model. Model building suggests that in the 2-D arrays, the two calponin homology domains that comprise the actin-binding domain have a closed conformation at one end and an open conformation at the other end due to domain swapping. The open and closed conformations of the actin-binding domain suggests flexibility that may underlie Ca2+ regulation. The approximately 90 degrees orientation difference at the molecular ends may underlie alpha-actinin's ability to crosslink actin filaments in nearly any orientation.
Related Citations:
Projection image of smooth muscle alpha-actinin from two-dimensional crystals formed on positively charged lipid layers Taylor, K.A., Taylor, D.W. (1993) J Mol Biol 230: 196
The three-dimensional structure of alpha-actinin obtained by cryoelectron microscopy suggests a model for Ca(2+)-dependent actin binding Tang, J., Taylor, D.W., Taylor, K.A. (2001) J Mol Biol 310: 845
Isoforms of alpha-actinin from cardiac, smooth and skeletal muscle form polar arrays of actin filaments Taylor, K.A., Taylor, D.W., Schachat, F. (2000) J Cell Biol 149: 635
Organizational Affiliation:
Institute of Molecular Biophysics, Florida State University, Tallahassee, FL 32306-4380, USA.
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