PyHI

PyHI determines symmetry parameters of helical assemblies from diffraction patterns and two-dimensional class averages using Fourier-Bessel indexing to support high-resolution structural analysis by electron microscopy.

Key Features:

• Data Input Flexibility: Accepts diffraction patterns directly or computes them on-the-fly from two-dimensional class averages of helical assemblies.
• Fourier-Bessel Indexing: Implements Fourier-Bessel indexing and addresses ambiguities in symmetry determination from diffraction patterns.
• Comprehensive Diffraction Analysis: Utilizes both amplitudes and phases of diffraction data to deduce Bessel orders of diffraction peaks.
• Fourier Space Lattice Construction: Constructs a Fourier space lattice from the Bessel orders of two unit vectors.
• Refinement Algorithm: Employs a refinement algorithm to optimize the constructed Fourier space lattice against experimental data.
• Real-Space Helical Assembly Generation: Generates real-space helical assemblies from the optimized Fourier space lattice.
• Symmetry Parameters Output: Produces critical symmetry parameters required for downstream reconstruction and high-resolution structure determination.

Scientific Applications:

• Structural Biology: Supports solving high-resolution structures of macromolecular helices analyzed by electron microscopy.
• Viral Capsids: Facilitates symmetry determination for helical viral capsids.
• Filamentous Proteins and Helical Macromolecules: Enables analysis of filamentous proteins and other helically organized macromolecules.

Methodology:

Fourier-Bessel indexing; calculation of diffraction patterns from two-dimensional class averages or direct diffraction input; analysis of amplitudes and phases to deduce Bessel orders; construction of a Fourier space lattice from Bessel orders of two unit vectors; refinement algorithm to optimize the lattice; generation of real-space helical assemblies from the optimized lattice.