Globular or end-to-end? A two-dimensional Spectrum Analysis for Assessing Modes of Aggregation from Sedimentation Velocity Experiments


  • Researchers are trying to understand subunit polymerization details, especially molecular weight and shape distributions in mixed solutions. A significant challenge is analyzing these when multiple components are present. The 2-dimensional spectrum analysis, introduced here, examines sedimentation velocity experiments to decipher aggregation modes. It can distinguish between fibril-type and globular aggregations. To process efficiently, the method leverages supercomputer parallelization.


  • We use the frictional ratio, k=f/f0, to parameterize the diffusion coefficient.
  • A sedimentation coefficient formula is applied.
  • The solute mixture is described using a model.
  • The NNLS algorithm compares the model to experimental data, b, identifying solute coefficients.
  • s and k=f/f0 values are estimated based on known protein and DNA molecule ranges.
  • A 2D mesh for each s, f/f0 pair is developed and refined.
  • Further refinement methods include maximum entropy regularization and genetic algorithm optimization, with the 2D analysis as a starting point.


  • The 2-dimensional spectrum analysis reliably describes systems with varied sedimentation coefficients and shapes, outperforming other methods in variance.
  • The method accurately represented a heterogeneous plasmid digest and two systems, "Mo27Fe30, Keplerate" and "Bindzil 30/360", distinct in molecular weight but consistent in shape.
  • Using this analysis, it's possible to determine both sedimentation and shape properties, helping to identify the aggregation mode of systems (e.g., fibril or globular).
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Comparability Studies
Material Science (metal nanoparticles, synthetic polymers, drug compounds)

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