Detergent Choice Shapes the Solution Structures of Photosystems I and II: Implications for Crystallization and High-Resolution Studies.

Photosystems I (PSI) and II (PSII) are pigment-protein complexes that perform the light-driven charge separation necessary to convert solar energy into a biochemically usable form in a fundamental process called photosynthesis. Small-angle X-ray scattering provides unique structural insights into PSI and PSII in solution under near-physiological conditions. Here, we study the solubilization of PSI and PSII with different detergents, the octaethylene glycol monododecyl ether (C12E8) and the most commonly used n-dodecyl-β-D-maltoside (DDM). It is noteworthy that the volume of the C12E8 detergent belt is more compact for PSI and PSII than for DDM. Furthermore, circular dichroism measurements were used to detect thermal destabilization in protein solutions containing C12E8. The impacts of the size, number, mobility, and stabilization of the C12E8 molecules in the PSII complex solution before crystallization and after detergent extraction in the crystal are discussed in terms of obtaining an improved X-ray structure.