Journal
JOURNAL OF MOLECULAR BIOLOGY
Volume 338, Issue 1, Pages 115-125Publisher
ACADEMIC PRESS LTD- ELSEVIER SCIENCE LTD
DOI: 10.1016/j.jmb.2004.02.034
Keywords
actin-binding protein; muscle protein; image processing; 2-D crystals; lipid monolayer; electron microscopy
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Funding
- NCRR NIH HHS [RR11357] Funding Source: Medline
- NIAMS NIH HHS [AR42872] Funding Source: Medline
- NIGMS NIH HHS [GM64346, U54 GM064346] Funding Source: Medline
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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 90degrees 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 similar to90degrees 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 similar to90degrees orientation difference at the molecular ends may underlie alpha-actinin's ability to crosslink actin filaments in nearly any orientation. (C) 2004 Elsevier Ltd. All rights reserved.
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