Membrane protein stability: high pressure effects on the structure and chromophore-binding properties of the light-harvesting complex LH2.
Using the bacteriochlorophyll a (Bchl) cofactors as intrinsic probes to monitor changes in membrane protein structure, we investigate the response to high-pressure of the LH2 complexes from the photosynthetic bacteria Rhodobacter sphaeroides 2.4.1 and Rhodopseudomonas acidophila 10050. By FT-Raman spectroscopy, we demonstrate that high pressure does not induce significant distortion of the protein-bound 850 nm-absorbing bacteriochlorophyll molecules, or break of the hydrogen bond they are involved in. This indicates in particular that the oligomerization of the polypeptides is not perturbed up to 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 is pressure independent and comprises mostly the C-terminal domain. The second domain located on the N-terminal side exhibits sensitivity to pressure and pH reminiscent of soluble proteins. The LH2 thus constitutes a suitable model system for studying in detail the stability of membrane-embedded hydrophobic helices and helices located at or close to the solvent/membrane interface.
Division of Biochemistry and Molecular Biology, IBLS, University of Glasgow, Glasgow G128QQ, Scotland. andrew.gall@bio.gla.ac.uk
Andrew
A
Gall
Aleksandr
A
Ellervee
James N
JN
Sturgis
Niall J
NJ
Fraser
Richard J
RJ
Cogdell
Arvi
A
Freiberg
Bruno
B
Robert
D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry; D001429:Bacteriochlorophylls / Q000737:chemistry*; D002338:Carotenoids / Q000737:chemistry; D045342:Light-Harvesting Protein Complexes / Q000737:chemistry*; D008565:Membrane Proteins / Q000737:chemistry*; D008969:Molecular Sequence Data; D011312:Pressure; D011485:Protein Binding; D020836:Protein Structure, Quaternary; D017434:Protein Structure, Tertiary; D012242:Rhodobacter sphaeroides / Q000737:chemistry; D012241:Rhodopseudomonas / Q000737:chemistry; D013053:Spectrophotometry; D013059:Spectrum Analysis, Raman; D013816:Thermodynamics
C081521:B800-850 light-harvesting complex, bacteria; D001426:Bacterial Proteins; D001429:Bacteriochlorophylls; D045342:Light-Harvesting Protein Complexes; D008565:Membrane Proteins; C104880:spheroidenone; D002338:Carotenoids