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Updated: Sep 14, 2025

Structure of HIV-1 Capsid Assemblies by Cryo-electron Microscopy and Iterative Helical Real-space Reconstruction
Published on: August 9, 2011
Accurate helical parameter estimation based on cylindrical unrolling
Mingtao Huang1, Jinying Ma2, Xiaoyu Fu2
1Key Laboratory for Protein Sciences of Ministry of Education, School of Life Sciences, Tsinghua University, Beijing 100084, China; Tsinghua-Peking Joint Center for Life Sciences, Beijing 100084, China; Beijing Frontier Research Center for Biological Structure, Beijing 100084, China; State Key Laboratory of Membrane Biology, School of Life Sciences, Tsinghua University, Beijing 100084, China; School of Life Sciences, Tsinghua University, Beijing 100084, China; Department of Electronic Engineering, Tsinghua University, Beijing 100084, China; Beijing National Research Center for Information Science and Technology, Tsinghua University, Beijing 100084, China.
None:
Helical structure is fundamental for filamentous and tubular macromolecular assemblies that play crucial roles in structural scaffolding and signaling processes. Structure determination of these assemblies relies on the precise estimation of their helical parameters. Although layer-line-based methods are widely used, their application is often challenging due to structural flexibility and heterogeneity. Herein, we report a method for helical parameter estimation based on cylindrical unrolling, called helix is simple (HELIS), which is implemented in a software package with the same name. HELIS treats helical structures as rolled two-dimensional (2D) crystals. Estimation of the helical parameters of structures visualized by cryo-electron tomography (cryo-ET) is derived from simplified 2D reciprocal-lattice measurements. HELIS also incorporates auxiliary algorithms to trace and unbend curved filaments, determine relative polarity, and perform in situ helical reconstruction. HELIS is a comprehensive helical structure determination tool with high accuracy for helical parameter estimation that is applicable to various helical assemblies.
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