Correction of rhodopsin serial crystallography diffraction intensities for a lattice-translocation defect

Abstract

Rhodopsin is a G-protein-coupled receptor that detects light and initiates the intracellular signalling cascades that underpin vertebrate vision. Light sensitivity is achieved by covalent linkage to 11-cis retinal, which isomerizes upon photoabsorption. Serial femtosecond crystallography data collected from rhodopsin microcrystals grown in the lipidic cubic phase were used to solve the roomtemperature structure of the receptor. Although the diffraction data showed high completeness and good consistency to 1.8 A degrees resolution, prominent electron-density features remained unaccounted for throughout the unit cell after model building and refinement. A deeper analysis of the diffraction intensities uncovered the presence of a lattice-translocation defect (LTD) within the crystals. The procedure followed to correct the diffraction intensities for this pathology enabled the building of an improved resting-state model. The correction was essential to both confidently model the structure of the unilluminated state and interpret the light-activated data collected after photoexcitation of the crystals. It is expected that similar cases of LTD will be observed in other serial crystallography experiments and that correction will be required in a variety of systems.