Abstract
It has long been established that diacyl phospholipids isolated from animal cell membranes are predominantly of a mixed-chain variety, meaning that the sn-1 and sn-2 acyl chains are saturated and unsaturated acyl chains, respectively. In general, monoenoic and dienoic acids are found in the sn-2 acyl chain of phosphatidylcholine (PtdCho), whereas polyenoic acids are in phosphatidylethanolamine (PtdEth). These unsaturated chains contain only cis-double bonds, which are always methylene-interrupted. In recent years, the structures and the chain-melting behavior of mixed-chain PtdCho and PtdEth have been systematically studied in this laboratory. Specifically, we have examined the effects of chain unsaturation of the sn-2 acyl chain on the phase transition temperature (Tm) of many PtdCho and PtdEth by high-resolution differential scanning calorimetry (DSC). The Tm values, for instance, obtained from all-unsaturated mixed-chain PtdEth derived from a common precursor can be grouped together according to their chemical formula to form a Tm-diagram. Hence, all the Tm values can be compared simply, systematically, and simultaneously using the Tm-diagram. In addition, the energy-minimized structures of mixed-chain phospholipids containing different numbers/positions of methylene-interruped cis-double bonds have been simulated by molecular mechanics calculations (MM). In this review, the results of our MM and DSC studies carried out with various mixed-chain phospholipids are summarized. In addition, we emphasize that the combined approach of MM and DSC yields unique uniformation that can correlate the various Tm-profiles seen in the Tm-diagram with the structural variation of mixed-chain lipids as caused by the introduction of different numbers/positions of methylene-interrupted cis-double bonds.
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Abbreviations
- ATS:
-
all-trans segment
- ΔC:
-
effective chain length differenence, as measured in C−C bonds, between the sn-1 and the sn-2 acyl chains, an indication of chain asymmetry
- ΔCref :
-
effective chain length difference of the reference state [or, effective chain length difference between the sn-1 and sn-2 acyl chains]
- CL:
-
effective chain length of the longer of the two acyl chains
- DSC:
-
differential scanning calorimetry
- MM:
-
molecular mechanics
- N:
-
distance, in C−C bond lengths, between the two carbonyl oxygens of the sn-1 acyl chains in a trans-bilayer dimer of C(X):C(Y) PtdCho
- PtdCho:
-
phosphatidylcholine
- PtdEth:
-
phosphatidylethanolamine
- PtdGro:
-
phosphatidylglycerol
- Ptd2Gro:
-
Cardiolipin (=diphosphatidylglycerol)
- PtdIns:
-
phosphatidylinositol
- PtdSer:
-
phosphatidylserine
- Tm :
-
main phase transition temperature
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Huang, Ch. Mixed-chain phospholipids: Structures and chain-melting behavior. Lipids 36, 1077–1097 (2001). https://doi.org/10.1007/s11745-001-0818-1
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DOI: https://doi.org/10.1007/s11745-001-0818-1