tailieunhanh - Báo cáo khoa học: Thermodynamics of the b2 association in light-harvesting complex I of Rhodospirillum rubrum Implication of peptide identity in dimer stability

The core light-harvesting LH1 protein fromRhodospirillum rubrumcan dis-sociate reversibly in the presence ofn-octyl-b-d-glucopyranoside into smal-ler 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). | ễFEBS Journal Thermodynamics of the p2 association in light-harvesting complex I of Rhodospirillum rubrum Implication of peptide identity in dimer stability Jerome Seguin1 Claudine Mayer2 Bruno Robert1 and Veronique Arluison3 1 CEA iBiTecS URA 2096 CNRS SB2SM Gif Yvette France 2 LRMA Universite Paris 6 France 3 IBPC CNRS UPR 9073 conventionnee avec l universite Paris VII France Keywords bacteriochlorophyll light harvesting complex membrane protein purple photosynthetic bacteria transmembrane a helix Correspondence V. Arluison IBPC CNRS UPR 9073 conventionnee avec l universite Paris VII 13 rue P. et M. Curie 75005 Paris France Fax 33 1 58 41 50 20 Tel 33 1 58 41 51 39 E-mail Received 9 October 2007 revised 16 December 2007 accepted 9 January 2008 The core light-harvesting LH1 protein from Rhodospirillum rubrum can dissociate reversibly in the presence of n-octyl-p-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-p-D-glucopyranoside we have previously shown that the B820 form is not only constituted by the aP heterodimer alone but that it exists in an equilibrium between the aP heterodimer and p2 homodimer states. We investigated the dissociation equilibrium for both oligomeric B820 forms. Using a theoritical model for aP and P2 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. doi The primary step in the photosynthetic process in purple bacteria consists of photon absorption by lightharvesting LH pigment-protein complexes. LH ensures the rapid and efficient transfer of excitation energy towards the photosynthetic reaction centre RC where the primary charge separation takes place. In .