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Deep-etch visualization of 27S clathrin: a tetrahedral tetramer
J E Heuser1, J H Keen, L M Amende
1Department of Cell Biology and Physiology, Washington University School of Medicine, St. Louis, Missouri 63110.
The Journal of Cell Biology
|November 1, 1987
Summary
Clathrin trimers form 27S tetrahedral structures in low ionic strength buffers. These closed tetrahedra, composed of four clathrin triskelions, represent a novel symmetrical assembly.
Area of Science:
- Biochemistry
- Structural Biology
- Molecular Biophysics
Background:
- Clathrin molecules, known as triskelions, assemble into larger structures.
- Previously, 8S clathrin trimers were reported to form 27S oligomers in low ionic strength buffers.
Purpose of the Study:
- To elucidate the structure of the 27S clathrin oligomers.
- To understand the assembly of clathrin in conditions favoring non-cage structures.
Main Methods:
- Deep-etch electron microscopy of quick-frozen and freeze-etched 27S clathrin species.
- Modified freeze-drying on polylysine-treated mica.
- Light scattering and equilibrium centrifugation.
Main Results:
- The 27S species were identified as closed tetrahedra with edges of 33 nm, formed by four clathrin triskelions.
- Electron microscopy revealed four globular domains linked by struts, resembling vertices and legs of triskelions.
- Mass analysis confirmed the 27S polymer is four times the mass of a single triskelion.
Conclusions:
- Low-affinity interactions drive the formation of symmetrical, closed tetrahedral assemblies of four clathrin triskelions under specific buffer conditions.
- These tetrahedra represent a distinct clathrin assembly, smaller than previously described cubic octomers.
- Triskelions adopt a puckered, straight-legged configuration to form the tetrahedral edges.