Data analysis and modeling of small-angle neutron scattering data with contrast variation from bio-macromolecular complexes

Whitten, Andrew E.; Jeffries, Cy M.

doi:10.1016/bs.mie.2022.09.015

Cited by 1 publication

(1 citation statement)

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“…Without SEC, the SANS signals of various constituents of the polydisperse solutions would be averaged and difficult to deconvolute. In contrast, using SEC-SANS fractions of different molecular masses can be analyzed separately, revealing their sizes and shapes in solution [ 37 , 38 ]. SANS has been widely used in various protein systems, including studies on protein folding [ 39 ], ligand–protein interactions [ 40 ], and the structural analysis of protein complexes, providing valuable insights into the mechanisms of biological processes.…”

Section: Introductionmentioning

confidence: 99%

Solution Structures of Two Different FRP-OCP Complexes as Revealed via SEC-SANS

Hajizadeh,

Golub,

Moldenhauer

et al. 2024

IJMS

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Photosynthetic organisms have established photoprotective mechanisms in order to dissipate excess light energy into heat, which is commonly known as non-photochemical quenching. Cyanobacteria utilize the orange carotenoid protein (OCP) as a high-light sensor and quencher to regulate the energy flow in the photosynthetic apparatus. Triggered by strong light, OCP undergoes conformational changes to form the active red state (OCPR). In many cyanobacteria, the back conversion of OCP to the dark-adapted state is assisted by the fluorescence recovery protein (FRP). However, the exact molecular events involving OCP and its interaction with FRP remain largely unraveled so far due to their metastability. Here, we use small-angle neutron scattering combined with size exclusion chromatography (SEC-SANS) to unravel the solution structures of FRP-OCP complexes using a compact mutant of OCP lacking the N-terminal extension (∆NTEOCPO) and wild-type FRP. The results are consistent with the simultaneous presence of stable 2:2 and 2:1 FRP-∆NTEOCPO complexes in solution, where the former complex type is observed for the first time. For both complex types, we provide ab initio low-resolution shape reconstructions and compare them to homology models based on available crystal structures. It is likely that both complexes represent intermediate states of the back conversion of OCP to its dark-adapted state in the presence of FRP, which are of transient nature in the photocycle of wild-type OCP. This study demonstrates the large potential of SEC-SANS in revealing the solution structures of protein complexes in polydisperse solutions that would otherwise be averaged, leading to unspecific results.

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