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Journal of Lipid Research, Vol. 45, 194-201, January 2004
Copyright © 2004 by American Society for Biochemistry and Molecular Biology

Osmotic shock stimulates de novo synthesis of two cardiolipins in an extreme halophilic archaeon

Patrizia Lopalco^*, Simona Lobasso, Francesco Babudri and Angela Corcelli^1,*

^* Dipartimento di Fisiologia Generale ed Ambientale, Università di Bari, Bari, Italy
Dipartimento di Chimica, Università di Bari, Bari, Italy

¹ To whom correspondence should be addressed. e-mail: a.corcelli{at}biologia.uniba.it

The present report illustrates the response to osmotic stress of an extreme halophilic archaeon, Halorubrum sp., isolated from the saltern ponds of Margherita di Savoia in southern Italy. The hypotonic stress induces relevant changes in the membrane lipid composition: archaeal cardiolipin content markedly increases, whereas phosphatidylglycerol (PG) decreases. Membranes isolated from this archaeon after cell disruption by osmotic shock are highly enriched in archaeal cardiolipin and reveal the presence of a novel phospholipid. Electrospray ionization mass spectrometry and NMR analyses revealed that this novel lipid has the structure of a sulfo-diglyco-diether-phosphatidic acid, i.e., a phospholipid dimer or a novel cardiolipin analogue. As NMR analyses showed that the sugars in the novel phospholipid dimer are the same and in the same order of a sulfated diglycosyl diphytanylglycerol diether (S-DGD-5) present as a major lipid component in the archaeon membranes, the novel phospholipid dimer was named S-DGD-5-PA.

We conclude that osmotic shock induces a specific increase in the membrane content of the two cardiolipins and suggest that PG and S-DGD-5 are intermediates for the de novo synthesis of archaeal cardiolipin and S-DGD-5-PA, respectively.

Abbreviations: BPG, bisphosphatidylglycerol or cardiolipin (diphytanylglycerol ether analogue); BR, bacteriorhodopsin; ESI-MS, electrospray ionization mass spectrometry; GlyC, glycocardiolipin or 3-HSO₃-Galp-ß1,6-Manp-1,2-Glcp-1,1-[sn-2,3-di-O-phytanylglycerol]-6-[phospho-sn-2,3-di-O-phytanylglycerol] or S-TGD-1-PA; PA, phosphatidic acid (diphytanylglycerol ether analogue); PG, phosphatidylglycerol (diphytanylglycerol ether analogue); PGP-Me, phosphatidylglycerophosphate methyl ester (diphytanylglycerol ether analogue); PGS, phosphatidylglycerosulfate (diphytanylglycerol ether analogue); PM, purple membrane; S-DGD-5, 2-HSO₃-Manp-1,2-Glcp-1,1-sn-2,3-diphytanylglycerol; S-DGD-5-PA, 2-HSO₃-Manp-1,2-Glcp-1,1-[sn-2,3-diphytanylglycerol]-6-[phospho-sn-2,3-diphytanylglycerol]; S-TGD-1, 3-HSO₃-Galp-ß1,6-Manp-1,2-Glcp-1,1-sn-2,3-diphytanylglycerol

Supplementary key words archaeal cardiolipin • sulfated diglycosyl diphytanylglycerol diether phosphatidic acid • halophiles • ARCHAEA

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