Protein/Lipid Interaction in the Bacterial Photosynthetic Reaction Center:  Phosphatidylcholine and Phosphatidylglycerol Modify the Free Energy Levels of the Quinones

• Published in: Biochemistry (Easton) 2004-10, Vol.43 (40), p.12913-12923
• Main Authors: Nagy, László, Milano, Francesco, Dorogi, Márta, Agostiano, Angela, Laczkó, Gábor, Szebényi, Kornélia, Váró, György, Trotta, Massimo, Maróti, Péter
• Format: Article
• Language: English
• Subjects: Amino Acids - metabolism; Cytochromes - metabolism; Electron Transport; Kinetics; Lipid Bilayers - chemistry; Lipid Bilayers - metabolism; Membranes, Artificial; Molecular Conformation; Phosphatidylcholines - metabolism; Phosphatidylglycerols - metabolism; Photosynthetic Reaction Center Complex Proteins - chemistry; Photosynthetic Reaction Center Complex Proteins - metabolism; Proteins - metabolism; Quinones - chemistry; Quinones - metabolism; Rhodobacter sphaeroides; Rhodobacter sphaeroides - chemistry; Rhodobacter sphaeroides - metabolism; Spectrum Analysis; Thermodynamics; Water - metabolism
• ISSN: 0006-2960; 1520-4995
• DOI: 10.1021/bi0489356

The role of characteristic phospholipids of native membranes, phosphatidylcholine (PC), phosphatidylglycerol (PG), and cardiolipin (CL), was studied in the energetics of the acceptor quinone side in photosynthetic reaction centers of Rhodobacter sphaeroides. The rates of the first, k AB(1), and the second, k AB(2), electron transfer and that of the charge recombination, k BP, the free energy levels of QA -QB and QAQB - states, and the changes of charge compensating protein relaxation were determined in RCs incorporated into artificial lipid bilayer membranes. In RCs embedded in the PC vesicle, k AB(1) and k AB(2) increased (from 3100 to 4100 s-1 and from 740 to 3300 s-1, respectively) and k BP decreased (from 0.77 to 0.39 s-1) compared to those measured in detergent at pH 7. In PG, k AB(1) and k BP decreased (to values of 710 and 0.26 s-1, respectively), while k AB(2) increased to 1506 s-1 at pH 7. The free energy between the QA -QB and QAQB - states decreased in PC and PG (ΔG°Q A − Q B → Q A Q B − = −76.9 and −88.5 meV, respectively) compared to that measured in detergent (−61.8 meV). The changes of the QA/QA - redox potential measured by delayed luminescence showed (1) a differential effect of lipids whether RC incorporated in micelles or vesicles, (2) an altered binding interaction between anionic lipids and RC, (3) a direct influence of PC and PG on the free energy levels of the primary and secondary quinones probably through the intraprotein hydrogen-bonding network, and (4) a larger increase of the QA/QA - free energy in PG than in PC both in detergent micelles and in single-component vesicles. On the basis of recent structural data, implications of the binding properties of phospholipids to RC and possible interactions between lipids and electron transfer components will be discussed.