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.