Thermodynamics of the beta(2) association in light-harvesting complex I of Rhodospirillum rubrum. Implication of peptide identity in dimer stability.
The core light-harvesting LH1 protein from Rhodospirillum rubrum can dissociate reversibly in the presence of n-octyl-beta-D-glucopyranoside into smaller subunit forms, exhibiting a dramatic blue-shift in absorption. During this process, two main species are observed: a dimer that absorbs at 820 nm (B820) and a monomer absorbing at 777 nm (B777). In the presence of n-octyl-beta-D-glucopyranoside, we have previously shown that the B820 form is not only constituted by the alphabeta heterodimer alone, but that it exists in an equilibrium between the alphabeta heterodimer and beta(2) homodimer states. We investigated the dissociation equilibrium for both oligomeric B820 forms. Using a theoretical model for alphabeta and beta(2), we conclude that the B820 homodimer is stabilized by both hydrophobic effects (entropy) and non-covalent bonds (enthalpy). We discuss a possible interpretation of the energy changes.
Seguin
Jérôme
J
Commissariat à l'Energie Atomique, iBiTecS, URA 2096 CNRS, SBSM, Gif/Yvette, France.
Mayer
Claudine
C
Robert
Bruno
B
Arluison
Véronique
V
D001426:Bacterial Proteins / Q000737:chemistry*; D019281:Dimerization; D019277:Entropy; D004795:Enzyme Stability; D005960:Glucosides / Q000737:chemistry; D045342:Light-Harvesting Protein Complexes / Q000737:chemistry*; D008958:Models, Molecular; D010455:Peptides / Q000737:chemistry; D011487:Protein Conformation; D012247:Rhodospirillum rubrum / Q000201:enzymology*
D001426:Bacterial Proteins; D005960:Glucosides; D045342:Light-Harvesting Protein Complexes; D010455:Peptides; C094744:light-harvesting complex 1, Rhodospirillum; C018619:octyl-beta-D-glucoside