Phosphatidylglycerols

FIGURE 8.6 Structures of several glycerophospholipids and space-filling models of phosphatidylcholine, phosphatidylglycerol, and phosphatidylinositol. 

B, phosphatidylethanolamine C, phosphatidylglycerol D, diphosphatidylglycerol (cardiolipin). Ra.COO and Rb.COO are fatty acid residues. 

Six two-component models were tested under sink conditions (models 5.1-10.1 in Table 7.3), employing three negatively charged lipids (dodecylcarboxylic acid, phosphatidic acid, and phosphatidylglycerol). These models were also tested in the absence of the sink condition (models 5.0-10.0 in Table 7.3). 

DOPC with Phosphatidylglycerol under Sink Conditions... 

Figure 5. Chemical structures of main lipids of purple membranes from Halobacterium salinarium S9 phosphatidylglycerophosphate (PGP), phosphatidylglycerol (PG) and glycolipid sulfate (GLS).

The architecture of the CM bilayer is symmetrical, with an equal distribution of the lipids (exclusively phospholipids, mainly phosphatidylethanolamine, phosphatidylglycerol and cardiolipin) among the inner and the outer leaflet. In principle, this holds true for most bacteria, except for those living at extremely high temperatures. For further information, see also Chapter 1 of this volume. 

Other alternatives are the lyso-phosphatidylglycerol derivatives in which one of the fatty acid chains coupled to glycerol have been removed. Unfortunately, the phosphatidyl lipids are not available in fully deuterated form, and hence certain regions of the proton spectra will be covered by the glycerol protons. 

Today s mitochondria lack most of the genes involved in phosphohpid metabolism. Therefore, mitochondria have to import most of their hpids. Phospholipids such as phosphatidylcholine, phosphatidylserine, phosphatidylglycerol, and phosphatidylinositol must be synthesized in the endoplasmatic reticulum under the control of nuclear genes and then transferred to mitochondria (Voelker, 2000) (Figure 1). Mitochondria use both nuclear and mitochondrial encoded proteins to further diversify phospholipids (Dowhan, 1997 Kent, 1995 Daum, 1985). Thus, a nuclear phosphatidylserine decarboxylase converts phosphatidylserine into phosphatidylethanolamine, or mitochondrial encoded cardiolipin synthase converts phosphatidylglycerol into cardiolipin which is incorporated exclusively into the inner mitochondrial membrane. 

Figure 1. Control of mitochondrial biogenesis by the nuclear genome. Most mitochondrial proteins, including cytochrome c, are nuclear gene products which are subsequently imported into mitochondria. Similarly, most enzymes involved in synthesis of mitochondrial phosphoplipids are encoded in the nuclear genome. Being located in the endoplasmatic reticulum, they synthesize phosphatidylcholine (PtdCho), phosphatidylserine (PtdSer), phosphatidylglycerol (PG) and phosphatidylinositol (Ptdins). The phospholipids are transferred to the outer membrane. The imported lipids then move into the inner membrane at contact sites. Mitochondria then diversify phospholipids. They decarboxylate phosphatidylserine to phosphatidylethanolamine (PtdEtN), but the main reaction is the conversion of imported phosphatidylglycerol to cardiolipin (CL). Cardiolipins localize mainly in the outer leaflet of the inner membrane.

Abbreviations. AmB, amphotericin B DMPC, drmyristoyl phosphatidylcholine DMPG, dimyristoyl phosphatidylglycerol. 

Abbreviations DOPS, dioleoylphosphatidylserine DLPE, dilauroylphosphatidylethanolamine POPC, palmitoyloleoylphosphatidylcholine DOPG, dioleoyl phosphatidylglycerol SM, sphingomyeline. 

The same type of experiments performed for phosphatidylglycerol (PG) content of liposomes showed a similar trend, but not as pronounced as in the case of PS. Here about 40% of the DCs and 8% of the T-cells showed binding to liposomes containing 50% PG. Influence of PE-content on the binding to these cells was not of great significance (data not shown). 

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