Symmetry and planar chirality of a protein measured on an angular basis in a transmission electron microscope

TL;DR

This paper introduces a new method using electron orbital angular momentum to measure planar chirality and symmetry in proteins, enhancing cryo electron microscopy analysis and 3D reconstruction speed.

Contribution

A novel composite planar chirality operator and measurement approach using electron OAM to analyze protein structures in cryo EM.

Findings

Unveiled atomic structures of biomolecules using electron OAM

Enabled faster protein identification in cryo EM

Improved 3D reconstruction accuracy and speed

Abstract

In quantum mechanics, each conserved quantity (e.g., energy, position, linear momentum and angular momentum) is associated with a Hermitian operator. Its expected value can then be determined by performing a measurement on the wavefunction. In modern electron microscopy, one can select the initial and final states of the electron and the measurement basis by performing measurements of scattering processes. For example, the orbital angular momentum (OAM) of an electron can be used to reveal the n-fold symmetry of a wavefunction scattered by a sample. Here, we introduce a new composite planar chirality operator that can be used to measure a spiral-like feature in a sample. This concept develops the concept of chirality to highlight a specific roto-scale symmetry. We show that planar chirality can be characterized using an electron OAM sorter to uncover the atomic structures of biomolecules in cryo electron microscopy, either in a stand-alone analysis for fast identification of protein structures or in the context of conventional cryo electron microscopy to produce faster and more detailed 3D reconstructions by solving upside-down orientation ambiguities.