Analysis of the Electronic Structure of the Special Pair of a Bacterial Photosynthetic Reaction Center by C-13 Photochemically Induced Dynamic Nuclear Polarization Magic-Angle Spinning NMR Using a Double-Quantum Axis

作者：Najdanova Marija; Graesing Daniel; Alia A; Matysik Joerg^*

来源：Photochemistry and Photobiology, 2018, 94(1): 69-80.

DOI：10.1111/php.12812

The origin of the functional symmetry break in bacterial photosynthesis challenges since several decades. Although structurally very similar, the two branches of cofactors in the reaction center (RC) protein complex act very differently. Upon photochemical excitation, an electron is transported along one branch, while the other remains inactive. Photochemically induced dynamic nuclear polarization (photo-CIDNP) magic-angle spinning (MAS) C-13 NMR revealed that the two bacteriochlorophyll cofactors forming the Special Pair donor dimer are already well distinguished in the electronic ground state. These previous studies are relying solely on C-13-C-13 correlation experiments as radio-frequency-driven recoupling (RFDR) and dipolar-assisted rotational resonance (DARR). Obviously, the chemical-shift assignment is difficult in a dimer of tetrapyrrole macrocycles, having eight pyrrole rings of similar chemical shifts. To overcome this problem, an INADEQUATE type of experiment using a POST C7 symmetry-based approach is applied to selectively isotope-labeled bacterial RC of Rhodobacter (R.) sphaeroides wild type (WT). We, therefore, were able to distinguish unresolved sites of the macromolecular dimer. The obtained chemical-shift pattern is in-line with a concentric assembly of negative charge within the common center of the Special Pair supermolecule in the electronic ground state.

• 出版日期2018-2
• 单位河北医科大学