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Journal of Lipid Research, Vol. 50, 256-264, February 2009
Copyright © 2009 by American Society for Biochemistry and Molecular Biology

Cardiolipin increases in chromatophores isolated from Rhodobacter sphaeroides after osmotic stress: structural and functional roles

Vincenzo De Leo^*, Lucia Catucci^1,*,, Andrea Ventrella^*, Francesco Milano, Angela Agostiano^*, and Angela Corcelli^,

^* Department of Chemistry, Università di Bari, Bari, Italy
Istituto per i Processi Chimico Fisici – Consiglio Nazionale delle Ricerche sez. Bari, Università di Bari, Bari, Italy
Department of Medical Biochemistry, Biology and Physics, Università di Bari, Bari, Italy

This work was supported by PRIN 2006 (Complessi Porfirinici Autoorganizzati su Scala Nanoscopica: Proprietà e Applicazioni Tecnologiche) of the Ministero Italiano dell'Università e della Ricerca Scientifica.

Published, JLR Papers in Press, August 20, 2008.

¹ To whom correspondence should be addressed. e-mail: catucci{at}chimica.uniba.it

Chromatophores isolated from cells of Rhodobacter sphaeroides exposed to hypertonic solutions were enriched in cardiolipin (CL). Because CL levels are raised by increasing the incubation time of R. sphaeroides in hypertonic solutions, it was possible to isolate chromatophores containing different CL amounts by starting from cells incubated in hypertonic solutions for different times. The functionality and stability of the photosynthetic proteins in chromatophore membranes having different CL levels were investigated. Reaction center (RC) stabilization with respect to thermal denaturation and photoxidative damage was observed by flash photolysis and fluorescence emission experiments in CL-enriched chromatophores. To gain detailed information about the structures of endogenous CLs, this lipid family was isolated and purified by preparative TLC, and characterized by high-resolution mass spectrometry. We conclude that osmotic shock can be used as a tool to modulate CL levels in isolated chromatophores and to change the composition of the RC lipid annulus, avoiding membrane artifacts introduced by the use of detergents.

Supplementary key words lipid-protein interactions • reaction center • thermal denaturation • photoxidative damage • flash photolysis

Abbreviations: Bchl, bacteriochlorophyll; Bpheo, bacteriopheophytin; CL, cardiolipin or bisphosphatidylglycerol; CR, charge recombination; ESI-MS, electrospray ionization mass spectrometry; MS, mass spectrometry; MS/MS, tandem mass spectrometry; PC, phosphatidylcholine; PE, phosphatidylethanolamine; PG, phosphatidylglycerol; RC, reaction center; SQDG, sulfoquinovosyldiacylglycerol

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