Abstract
In the purple membrane (PM) of Halobacterium salinarum is present a phospholipid dimer consisting of sulfo-triglycosyl-diether (S-TGD-1) esterified to the phosphate group of phosphatidic acid (PA), i.e., S-TGD-1-PA, called glycocardiolipin (GlyC) (Corcelli, A., M. Colella, G. Mascolo, F. P. Fanizzi, and M. Kates. A novel glycolipid and phospholipid in the purple membrane. 2000. Biochemistry. 39: 3318-3326). The GlyC content of whole cells, PM, and other cell fractions of H. salinarum have been analyzed. GlyC is a nonabundant phospholipid in H. salinarum cells, and it represents one of the major phospholipids of isolated PM. In this report, we show that a) GlyC is formed during the isolation of PM, b) GlyC increase in H. salinarum cells is specifically induced by osmotic shock, and c) in correspondence with GlyC increase, a decrease of S-TGD-1 levels occurs. The changes in membrane lipid composition observed during the isolation of PM are due to de novo synthesis of GlyC from S-TGD-1.
Highlights
In the purple membrane (PM) of Halobacterium salinarum is present a phospholipid dimer consisting of sulfo-triglycosyl-diether (S-TGD-1) esterified to the phosphate group of phosphatidic acid (PA), i.e., S-TGD-1-PA, called glycocardiolipin (GlyC)
Cardiolipin is present in bacterial membranes in relation to the function of generating an electrochemical potential for substrate transport and ATP synthesis; recent crystallographic studies have shown that a cardiolipin molecule is located on the intramembrane surface of the reaction center from Rhodobacter sphaeroides [14]
An archaeal bisphosphatidilglycerol or archaeal cardiolipin (BPG) and a glycocardiolipin (GlyC) have been found among residual lipids associated with delipidated BR fractions isolated from an engineered strain of H. salinarum [1] in the natural halophilic community inhabiting the crystallizer brines of salterns [17], in a number of isolates from the saltern ponds of Margherita di Savoia (Italy), and in validated strains available from culture collections [17]
Summary
In the purple membrane (PM) of Halobacterium salinarum is present a phospholipid dimer consisting of sulfo-triglycosyl-diether (S-TGD-1) esterified to the phosphate group of phosphatidic acid (PA), i.e., S-TGD-1-PA, called glycocardiolipin (GlyC) Combining ESI-MS data and proton and phosphorus nuclear magnetic resonance (NMR) data of the purified novel lipids, together with the identification of their acid degradation products, allowed the elucidation of the chemical structures of the novel PM phospholipids [2]. Their structures are, respectively, of a phosphosulfoglycolipid, 3-HSO3-Galp1-6Manp␣1-2Glcp␣1-1-[ sn -2,3-di- O -phytanylglycerol]-6-[phospho- sn -2,3-di- O -phytanylglycerol] (called glycocardiolipin, or GlyC), and a glyceroldiether analog of bisphosphatidylglycerol, sn-2,3di-O-phytanyl-1-phosphoglycerol-3-phospho-sn-2,3-di-O-phytanylglycerol (archaeal BPG) (Fig. 1).
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