Does the Reconstitution of RC-LH1 Complexes from Rhodopseudomonas acidophila Strain 10050 into a Phospholipid Bilayer Yield the Optimum Environment for Optical Spectroscopy?

• Published in: The journal of physical chemistry. B Vol. 117; no. 48; pp. 15004 - 15013
• Main Authors: Böhm, Paul S, Kunz, Ralf, Southall, June, Cogdell, Richard J, Köhler, Jürgen
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 05.12.2013
• Subjects: Biological and medical sciences; Buffer solutions; Detergents; Fundamental and applied biological sciences. Psychology; Immobilization; Light-Harvesting Protein Complexes - chemistry; Light-Harvesting Protein Complexes - metabolism; Lipid Bilayers - chemistry; Lipid Bilayers - metabolism; Models, Molecular; Molecular biophysics; Phospholipids; Phospholipids - chemistry; Phospholipids - metabolism; physical chemistry; polyvinyl alcohol; Polyvinyl alcohols; Proteins; Radiation-biomolecule interaction; Rhodopseudomonas; Rhodopseudomonas - chemistry; Rhodopseudomonas - enzymology; Rhodopseudomonas acidophila; Spectra; Spectrophotometry, Ultraviolet; Spectroscopy; Spectroscopy, Near-Infrared; statistics; Rhodospirillales; Light harvesting system; Medium effect; Phospholipid; Dipolar transition; Bacteria; Rhodospirillaceae; Rhodopseudomonas acidophila; Rhodospirillineae; Protein; Absorption spectrum; Bilayers
• DOI: 10.1021/jp409980k
• ISSN: 1520-6106; 1520-5207

We have investigated reaction-center light-harvesting 1 (RC-LH1) complexes from Rhodopseudomonas (Rps.) acidophila in detergent buffer solution and reconstituted into a phospholipid bilayer and compared the results with the outcome of an earlier study conducted on RC-LH1 immobilized in polyvinyl alcohol (PVA). The aim of this study was to test whether the immobilization of the complexes in a PVA matrix might lead to a deterioration of the proteins and thereby limit the accessible information that can be obtained from optical spectroscopy. It has been found that the complexes dissolved in a detergent buffer solution are subject to fast spectral dynamics preventing any meaningful application of single-molecule spectroscopy. In contrast, for the bilayer samples it is revealed that the reconstitution process results in a significantly larger fraction of broken complexes with respect to the preparation of the complexes in a PVA film. Moreover, we find that for the intact complexes the statistics of the key spectral features, such as the spectral separations of the bands and the mutual orientation of their transition-dipole moments, show no variation dependent on using either a bilayer or PVA as a matrix. Given the additional effort involved in the reconstitution process, the lower amount of intact RC-LH1 complexes and, concerning the decisive spectral details, the identical results with respect to embedding the complexes in a PVA matrix, we come to the conclusion that the immobilization of these proteins in a PVA matrix is a good choice for conducting low-temperature experiments on individual light-harvesting complexes.