The technique used here to get pictures of the folded proteins (cryo-electron microscopy, or cryo-EM) has seen steady improvements over the past couple of decades. [1] It’s analogous to room temperature light microscopy like you might have done in school, but with electrons instead of photons:
>Imaging biological objects in an electron microscope is, in principle, analogous in some respects to light-microscopic imaging of cell and tissue specimens mounted on glass slides. In light microscopy, visible photons serve as the source of radiation; once they pass through the specimen, they are refracted through glass optical lenses to form an image. In electron microscopy, the radiation is electrons, emitted by a source that is housed under a high vacuum, and then accelerated down the microscope column
The number of protein structures determined via cryo-EM is growing fast. Why is cryo-EM exciting for protein structure determination?
The primary technique for determining protein structures is X-ray crystallography, which, as the name implies, requires you to first produce, purify, and crystallize the protein. In contrast, cryo-EM allows determination of the protein structure without having to crystallize it.
In a typical cryo-EM experiment for protein structure determination, the protein molecules are imaged sparsely on a thin film, and many 2-D images are taken. These 2-D images are used to reconstruct the 3-D structure using a variety of computational techniques (including, recently, deep learning)
>images of the object, each with a different orientation, have 2D Fourier transforms that correspond to sections (indicated by red arrows) through the 3D Fourier transform of the original object. Thus, once the 3D Fourier transform is built up from a collection of 2D images spanning a complete range of orientations, Fourier inversion enables recovery of the 3D structure
In the analogous X-ray crystallography experiment, you have to grow crystals of your protein before imaging. The conditions that provide nice crystals are unknown and crystallization itself is sometimes completely out of the question, such as in this article where the authors are imaging a tissue sample
>Imaging biological objects in an electron microscope is, in principle, analogous in some respects to light-microscopic imaging of cell and tissue specimens mounted on glass slides. In light microscopy, visible photons serve as the source of radiation; once they pass through the specimen, they are refracted through glass optical lenses to form an image. In electron microscopy, the radiation is electrons, emitted by a source that is housed under a high vacuum, and then accelerated down the microscope column
The number of protein structures determined via cryo-EM is growing fast. Why is cryo-EM exciting for protein structure determination?
The primary technique for determining protein structures is X-ray crystallography, which, as the name implies, requires you to first produce, purify, and crystallize the protein. In contrast, cryo-EM allows determination of the protein structure without having to crystallize it.
In a typical cryo-EM experiment for protein structure determination, the protein molecules are imaged sparsely on a thin film, and many 2-D images are taken. These 2-D images are used to reconstruct the 3-D structure using a variety of computational techniques (including, recently, deep learning)
>images of the object, each with a different orientation, have 2D Fourier transforms that correspond to sections (indicated by red arrows) through the 3D Fourier transform of the original object. Thus, once the 3D Fourier transform is built up from a collection of 2D images spanning a complete range of orientations, Fourier inversion enables recovery of the 3D structure
In the analogous X-ray crystallography experiment, you have to grow crystals of your protein before imaging. The conditions that provide nice crystals are unknown and crystallization itself is sometimes completely out of the question, such as in this article where the authors are imaging a tissue sample
1. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3537914/