Determine the origin of excess density in the GroEL central cavity

Determine whether the density filling the central cavity observed in single-particle X-ray diffraction images of GroEL consists of water, salt, or protein.

Background

The paper compares the reconstructed electron density of detergent-solubilized photosystem I trimers with crystal and molecular-dynamics structures, noting that retained water, salt, and detergent may contribute to unresolved density. It relates this interpretation to an earlier single-particle diffraction experiment on GroEL, in which the central cavity also appeared to contain additional density.

The composition of that GroEL cavity density remains unresolved because the available diffraction data do not distinguish among water, salt, and protein. Resolving its origin would clarify how residual material carried into the gas phase contributes to low-resolution single-particle diffraction reconstructions.

References

A similar effect was observed in single-particle diffraction from GroEL, whose central cavity appeared filled with density, although it could not be determined whether this was water, salt or protein [8].

— Three-dimensional imaging of isolated membrane-protein complexes in vacuo with an X-ray laser  (2610.11729 - Ayyer et al., 8 Oct 2026) in Main text, paragraph discussing the comparison of the PS I reconstruction with molecular-dynamics models and Fig. 4