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Sample support system improves cryo-EM resolution

Gold foil reduces ice-layer buckling and sample movement

by Celia Henry Arnaud
October 10, 2020 | APPEARED IN VOLUME 98, ISSUE 39


Credit: Neil Grant/MRC Laboratory of Molecular Biology
The gold foil sample support consists of an array of 3-mm grids (gold circles) that each contain about 800 hexagons with more than 5,000 200-nm holes.
Credit: Science
In this transmission electron micrograph of an individual hexagonal grid from the gold foil, each dot represents a 200 nm hole.

Although cryo-electron microscopy is a powerful method for determining the structures of nanoparticles and biological molecules, it still faces challenges. For example, sample movement can cause image blurring and loss of resolution. Katerina Naydenova, Peipei Jia, and Chris Russo of the Medical Research Council Laboratory of Molecular Biology now show that buckling and subsequent deformation of the ice layer in which the particles are suspended causes this movement. A new sample support eliminates this buckling and reduces sample movement to less than 1 Å (Science 2020, DOI: 10.1126/science.abb7927). The sample support is gold foil with hexagonally arrayed round holes. The foil is suspended across a 3 mm hexagonal mesh grid with about 800 hexagons, each of which contains more than 5,000 holes smaller than 300 nm. To eliminate buckling, the ratio of the diameter of the holes to the thickness of the ice layer should be no more than 11:1. So, for a sample that is 30 nm thick, the holes need to be less than 330 nm to render the molecules motionless. The researchers determined the structure of a 223-kilodalton DNA-protecting protein, at a resolution of 1.9 Å. Eliminating the movement also allowed them to remove the effects of radiation damage from the final structure.



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