title: Fast and accurate reference-free alignment of subtomograms.
abstract: In cryoelectron tomography alignment and averaging of subtomograms, each dnepicting the same macromolecule, improves the resolution compared to the individual subtomogram. Major challenges of subtomogram alignment are noise enhancement due to overfitting, the bias of an initial reference in the iterative alignment process, and the computational cost of processing increasingly large amounts of data. Here, we propose an efficient and accurate alignment algorithm via a generalized convolution theorem, which allows computation of a constrained correlation function using spherical harmonics. This formulation increases computational speed of rotational matching dramatically compared to rotation search in Cartesian space without sacrificing accuracy in contrast to other spherical harmonic based approaches. Using this sampling method, a reference-free alignment procedure is proposed to tackle reference bias and overfitting, which also includes contrast transfer function correction by Wiener filtering. Application of the method to simulated data allowed us to obtain resolutions near the ground truth. For two experimental datasets, ribosomes from yeast lysate and purified 20S proteasomes, we achieved reconstructions of approximately 20Å and 16Å, respectively. The software is ready-to-use and made public to the community.
authors.affiliation: Max-Planck Institute of Biochemistry, Department of Molecular Structural Biology, D-82152 Martinsried, Germany.
authors.forename: Yuxiang
authors.initials: Y
authors.lastname: Chen
authors.forename: Stefan
authors.initials: S
authors.lastname: Pfeffer
authors.forename: Thomas
authors.initials: T
authors.lastname: Hrabe
authors.forename: Jan Michael
authors.initials: JM
authors.lastname: Schuller
authors.forename: Friedrich
authors.initials: F
authors.lastname: Förster
mesh_terms: D000465:Algorithms; D020285:Cryoelectron Microscopy / Q000379:methods*; D055032:Electron Microscope Tomography; D007091:Image Processing, Computer-Assisted; D021621:Imaging, Three-Dimensional; D046988:Proteasome Endopeptidase Complex / Q000648:ultrastructure; D012270:Ribosomes / Q000648:ultrastructure; D012984:Software; D015003:Yeasts / Q000648:ultrastructure
chemical_list: D046988:Proteasome Endopeptidase Complex