Why Are Regions Missing From My Cryo-EM Structure? 7 Causes Of Unresolved Density And How To Investigate Them

By Austin Gamble Jarvi

Cryo-electron microscopy has made it possible to resolve complex biological structures in remarkable detail, but even a strong reconstruction may contain regions with weak, unclear, or missing density. These gaps can appear in flexible loops, protein termini, individual domains, side chains, ligand-binding regions, and protein-protein interaction sites. While missing density is often interpreted as disorder, the explanation may be more complex. Local flexibility, multiple conformational states, incomplete occupancy, compositional heterogeneity, preferred orientations, alignment uncertainty, and reconstruction limitations can all affect what is visible. Understanding these possibilities is essential for separating true biological behavior from experimental effects.

Learn how to interpret missing density more carefully and identify the questions that a solved structure may still leave open.