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Organizers: Joakim Andén, Dorit Hanein, Roy R. Lederman and Steven J. Ludtke

All Talks – Past talks – Upcoming Talks

Next Talk

Erik Thiede
Asst. Professor of Chemistry and Chemical Biology, Cornell University

Date and time: December 3rd, 2025 Wednesday at 8am PST / 11am EST / 4pm GMT / 5pm CET / 12am China

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Deconstructing Algorithms for “Discrete” Heterogeneity in Cryo-EM

Classic approaches to analyzing conformational or compositional heterogeneity in cryo-EM model attempt to recover a discrete set of structures from the data.  But despite how common these algorithms are, exactly how these structures relate to the structures the molecule observes in solution is not fully understood. In this talk, we revisit the likelihood-based algorithm for finding discrete classes.  By considering the limit of a large number of structures, we show that this algorithm can be viewed as an approach to solving a stochastic inverse problem for the latent structural probability density.  This gives us a new understanding of how the algorithm behaves in the limit of large data.  Moreover, our analysis gives a systematic way to construct new algorithms for recovering probability densities associated withheterogeneous data.  As an initial contribution, we introduce an algorithm based on the Wasserstein gradient flow.  Our work points the way towards more efficient and noise-robust algorithms for recovering heterogeneity with quantitative accuracy.

Diego Sanchez Espinosa, Erik Thiede, Yunan Yang.

Last Talk

Peter Van Blerkom
Researcher, UC Santa Barbara

Date and time: October 8th, 2025 Wednesday at 8am PST / 11am EST / 4pm GMT / 5pm CET / 12am China

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The GoldX Fiducial Eraser

Gold nanoparticles are standard fiducial markers in cryogenic electron tomography but often cause reconstruction artifacts due to their high electron density. We present a post-processing tool that automatically detects and suppresses these particles by replacing them with the local background. The method yields cleaner tomograms without loss of sample information or introduction of new artifacts, enabling more accurate visualization and interpretation of native cellular structures. 

References:
Van Blerkom P, Bezault A, Sauvanet C, Hanein D, Volkmann N. The GoldX Fiducial Eraser. International Journal of Molecular Sciences. 2024; 25(13):7442. https://doi.org/10.3390/ijms25137442