Optimization of a Cryo-EM Structural Model Representation

Abstract

Electron cryo-microscopy (cryoEM) has been used to resolve atomic resolution biological structures. However, the resulting density maps and models still lack assessment of accuracy and reproducibility. The densities of some residues particularly, the negative charged residues have been found to be consistently absent or have low values in near-atomic resolution cryoEM maps. We thus introduce a procedure to derive an atomic model that faithfully replicates the experimental map and then use this map to ensure data accuracy and reproducibility. We have applied this protocol to describe the 3.3 A structure of the mature P22 bacteriophage capsid, a large and complex macromolecular assembly. This structure identifies previously unknown molecular interactions between capsid subunits, crucial to maintaining particle stability.Acknowledgement: This research has been supported by NIH grants (R01GM079429, P01GM063210, T15LM007093) and R Welch Foundation (Q1242).