The three-dimensional structure of alpha-actinin obtained by cryoelectron microscopy suggests a model for Ca(2+)-dependent actin binding.
The three-dimensional structure of alpha-actinin from rabbit skeletal muscle was determined by cryoelectron microscopy in combination with homology modeling of the separate domain structures based on results previously determined by X-ray crystallography and nuclear magnetic resonance spectroscopy. alpha-Actinin was induced to form two-dimensional arrays on a positively charged lipid monolayer and micrographs were collected from unstained, frozen hydrated specimens at tilt angles from 0 degrees to 60 degrees. Interpretation of the 15 A-resolution three-dimensional structure was done by manually docking homologous models of the three key domains, actin-binding, three-helix motif and the C-terminal calmodulin-like domains. The initial model was refined quantitatively to improve its fit to the experimental reconstruction. The molecular model of alpha-actinin provides the first view of the overall structure of a complete actin cross-linking protein. The structure is characterized by close proximity of the C-terminal, calmodulin-like domain to the linker between the two calponin-homology domains that comprise the actin-binding domain. This location suggests a hypothesis to explain the involvement of the C-terminal domain in Ca(2+)-dependent actin binding of non-muscle isoforms.
Tang
J
J
Institute of Molecular Biophysics, Florida State University, Tallahassee, FL 32306-4380, USA.
Taylor
D W
DW
Taylor
K A
KA
D000185:Actinin / Q000737:chemistry / Q000378:metabolism* / Q000648:ultrastructure*; D000199:Actins / Q000378:metabolism*; D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology*; D002147:Calmodulin / Q000737:chemistry; D002851:Chromatography, High Pressure Liquid; D020285:Cryoelectron Microscopy; D005583:Fourier Analysis; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011485:Protein Binding / Q000187:drug effects; D020836:Protein Structure, Quaternary / Q000187:drug effects; D017434:Protein Structure, Tertiary / Q000187:drug effects; D011817:Rabbits; D016415:Sequence Alignment
D000199:Actins; D002147:Calmodulin; D000185:Actinin; D002118:Calcium