| Abstract
| - Using the bacteriochlorophyll a (Bchl) cofactors as intrinsic probes to monitor changes inmembrane protein structure, we investigate the response to high-pressure of the LH2 complexes from thephotosynthetic bacteria Rhodobacter sphaeroides 2.4.1 and Rhodopseudomonas acidophila 10050. ByFT-Raman spectroscopy, we demonstrate that high pressure does not induce significant distortion of theprotein-bound 850 nm-absorbing bacteriochlorophyll molecules, or break of the hydrogen bond they areinvolved in. This indicates in particular that the oligomerization of the polypeptides is not perturbed upto 0.6 GPa. The pressure-induced changes in the Bchl absorption spectra are attributed to pigment−pigment interactions. In contrast, the loss of 800 nm-absorbing bacteriochlorophyll reflects pressure-induced alterations to the tertiary structure of the protein in proximity to the membrane/cytosol interface.This suggests that the LH2 protein does have two independent structural domains. The first domain ispressure independent and comprises mostly the C-terminal domain. The second domain located on theN-terminal side exhibits sensitivity to pressure and pH reminiscent of soluble proteins. The LH2 thusconstitutes a suitable model system for studying in detail the stability of membrane-embedded hydrophobichelices and helices located at or close to the solvent/membrane interface.
|
