1. k8凯发

      Image processing and 3D reconstruction

      Minghao Chen

      Published: 2023-10-17 DOI: 10.17504/protocols.io.x54v9d99mg3e/v1
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      Abstract

      Image processing and 3D reconstruction

      Steps

      Image processing

      1.

      Use cryoSPARC for the following steps except those particularly mentioned.

      2.

      Do motion correction by [Patch Motion Correction]

      Bin 2x in fourier cropping for super-resolution video stacks

      Bin 1x in fourier cropping for regular video stacks

      3.

      Do contrast transfer function determination by [Patch CTF Estimation]

      Remove the outlier micrographs base on the estimated defocus and resolution value.

      4.

      Do particle picking by [Topaz]

      Manually pick 10 micrographs as learning dataset

      Optimize the 'picking threshold' with the 10 mics

      Apply the parameter to the entile dataset

      5.

      Particle extraction

      Use the box size 1.5 times larger than the target particles

      Bin 4x to facilitate the following classification jobs

      6.

      2D classification

      Set 50-100 classes dependent on the data size

      Remove the obvious junk particles

      7.

      Obtain an initial model

      [1] Use Ab-initial (Optional) only select the 2D classes that show high-resolution features

      [2] Use previously determined structure if it's available

      [3] Create a new medel by AlphaFold

      8.

      Do 3D classification by [Reterogeneous Refinement]

      Low-pass your model to 15-20 Å

      Run the job with 2-3 junk models

      Run multiple times (typically 2-4 rounds) until the result converges

      9.

      Re-extract the particles with

      bin 2x for super-resolution video stacks

      bin 1x for regular video stacks

      3D reconstruction

      10.

      Do 3D reconstruction by [Homogeneous Refinement]

      Repeat 2-3 times until the resolution converges

      Check whether the FSC curve is healthy

      11.

      (Optional)

      Do CTF refiment followed by homogeneous refinement.

      Check whether the resolution get improved

      12.

      (Optional)

      Do local refinement if the map contains multiple rigid sub-regions

      Decide the masks based on [3D Variability] or [3D Flex]

      Use [ChimeraX] to create the maps

      Use [EMAN2] to compose the final maps at the end

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