Modeling Beta-Traces for Beta-Barrels from Cryo-EM Density Maps

Cryo-electron microscopy (cryo-EM) has produced density maps of various resolutions. Although alpha-helices can be detected from density maps at 5-8 angstrom resolutions, beta-strands are challenging to detect at such density maps due to close-spacing of beta-strands. The variety of shapes of beta-sheets adds the complexity of beta-strands detection from density maps. We propose a new approach to model traces of beta-strands for beta-barrel density regions that are extracted from cryo-EM density maps. In the test containing eight beta-barrels extracted from experimental cryo-EM density maps at 5.5 angstrom-8.25 angstrom resolution, StrandRoller detected about 74.26% of the amino acids in the beta-strands with an overall 2.05 angstrom 2-way distance between the detected beta-traces and the observed ones, if the best of the fifteen detection cases is considered.