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J Biol Chem. 2017 Apr 28;292(17):7077-7086. doi: 10.1074/jbc.M116.769778. Epub 2017 Mar 15.

Structural and functional characterization of Caenorhabditis elegans α-catenin reveals constitutive binding to β-catenin and F-actin.

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From the School of Biological Sciences, Seoul National University, Seoul 08826, South Korea.
the Pohang Accelerator Laboratory, Pohang, Gyeongbuk 37673, South Korea.
the Department of Biophysics and Chemical Biology and.
the Institute of Molecular Biology and Genetics, Seoul National University, Seoul 08826, South Korea.
the Department of Zoology and Program in Genetics, University of Wisconsin, Madison, Wisconsin 53706.
the Department of Cell Biology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15261, and.
the Departments of Biology.
Molecular and Cellular Physiology, and.
Structural Biology, Stanford University School of Medicine, Stanford, California 94305.
From the School of Biological Sciences, Seoul National University, Seoul 08826, South Korea,


Intercellular epithelial junctions formed by classical cadherins, β-catenin, and the actin-binding protein α-catenin link the actin cytoskeletons of adjacent cells into a structural continuum. These assemblies transmit forces through the tissue and respond to intracellular and extracellular signals. However, the mechanisms of junctional assembly and regulation are poorly understood. Studies of cadherin-catenin assembly in a number of metazoans have revealed both similarities and unexpected differences in the biochemical properties of the cadherin·catenin complex that likely reflect the developmental and environmental requirements of different tissues and organisms. Here, we report the structural and biochemical characterization of HMP-1, the Caenorhabditis elegans α-catenin homolog, and compare it with mammalian α-catenin. HMP-1 shares overall similarity in structure and actin-binding properties, but displayed differences in conformational flexibility and allosteric regulation from mammalian α-catenin. HMP-1 bound filamentous actin with an affinity in the single micromolar range, even when complexed with the β-catenin homolog HMP-2 or when present in a complex of HMP-2 and the cadherin homolog HMR-1, indicating that HMP-1 binding to F-actin is not allosterically regulated by the HMP-2·HMR-1 complex. The middle (i.e. M) domain of HMP-1 appeared to be less conformationally flexible than mammalian α-catenin, which may underlie the dampened effect of HMP-2 binding on HMP-1 actin-binding activity compared with that of the mammalian homolog. In conclusion, our data indicate that HMP-1 constitutively binds β-catenin and F-actin, and although the overall structure and function of HMP-1 and related α-catenins are similar, the vertebrate proteins appear to be under more complex conformational regulation.


Caenorhabditis elegans (C. elegans); HMP-1; HMP-2; X-ray crystallography; actin; cell adhesion; four helix bundle; small-angle X-ray scattering (SAXS); α-catenin (a-catenin)

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