High-Resolution Single-Molecule Structure Revealed by Electron Microscopy and Individual Particle Electron Tomography

Area of Science:

• Structural Biology
• Biophysics
• Biochemistry

Background:

• Proteins are inherently dynamic and heterogeneous in solution.
• Conventional structural methods like X-ray crystallography and single-particle electron microscopy provide static snapshots, insufficient for capturing protein dynamics.
• Understanding protein dynamics is crucial for biological function and processes like energy conversion by molecular motors.

Purpose of the Study:

• To develop and demonstrate a method for determining the three-dimensional structure of individual protein particles.
• To overcome the limitations of existing techniques in visualizing dynamic and heterogeneous protein structures.
• To enable the study of protein dynamics through particle-by-particle structural comparisons.

Main Methods:

• Innovations in cryo-electron microscopy (cryoEM) sample preparation and operation for cryo-electron tomography (cryoET).
• Development of an optimized negative staining (OpNS) protocol to eliminate artifacts and enhance image contrast.
• Implementation of cryo-positive staining (cryoPS) for high-resolution visualization of protein secondary structures.
• Application of Individual Particle Electron Tomography (IPET), a novel high-throughput reconstruction method for individual protein structures.

Main Results:

• Achieved the first high-clarity, single-molecule 3D electron microscopy (EM) images of individual proteins, including an IgG antibody (14 Å resolution) and a 17nm high-density lipoprotein (HDL) (36 Å resolution).
• Demonstrated successful imaging of individual 17 nm HDL particles (120-200 kDa) using cryoET.
• Visualized secondary structures like β-strands and helical belts within proteins using cryoPS.
• Established IPET as a robust method capable of reconstructing individual protein structures, challenging previous assumptions.

Conclusions:

• The developed methods, particularly IPET, allow for the determination of individual protein structures from EM data.
• This particle-by-particle approach overcomes the limitations of averaging in conventional EM techniques.
• Opens new avenues for investigating protein dynamics and heterogeneity at the single-molecule level.