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Intramolecular hydrogen bonding in cardiolipin
W Hübner1, H H Mantsch, M Kates
1Steacie Institute for Molecular Sciences, National Research Council of Canada, Ottawa.
Insights
Intramolecular hydrogen bonding in cardiolipin (CL) was investigated using FT-IR spectroscopy. The C-OH group in hydrogenated CL provides a structural basis for proton conduction, unlike its deoxy analogue.
Area of Science:
- Biochemistry
- Spectroscopy
- Membrane Biophysics
Background:
- Cardiolipin (CL) is a key phospholipid in mitochondrial membranes.
- Proton conduction across membranes is crucial for cellular energy production.
- Understanding CL's molecular structure is vital for elucidating its function.
Purpose of the Study:
- To investigate intramolecular hydrogen bonding in beef heart cardiolipin (18:0-CL) and its synthetic deoxy analogue (16:0-dCL).
- To determine if hydrogen bonding provides a structural basis for proton conduction at the molecular level.
Main Methods:
- Fourier transform infrared (FT-IR) spectroscopy was employed.
- Experiments were conducted on aqueous dispersions, dry films, and CCl4 solutions.
- Differential scanning calorimetry (DSC) was used to determine phase transition temperatures (Tm).
Main Results:
- Evidence suggests intramolecular C-OH...PO2- hydrogen bonding in 18:0-CL, particularly in dry films and CCl4 solutions.
- This bonding was absent in the 16:0-dCL analogue, indicating the importance of the central C-OH group.
- A significant increase in Tm upon switching from H2O to D2O in aqueous dispersions of 18:0-CL supports C-OH hydrogen bonding.
Conclusions:
- The central C-OH group in 18:0-CL plays a role in forming intramolecular hydrogen bonds with phosphate groups.
- These hydrogen bonds offer a potential structural basis for proton conduction in cardiolipin molecules.
- The findings contribute to understanding cardiolipin's role in membrane function and proton transport.
Abstract:
Fourier transform infrared (FT-IR) spectroscopy was used to determine whether intramolecular hydrogen bonding between the C-OH and P-OH groups exists in beef heart cardiolipin (CL) or in hydrogenated beef heart cardiolipin (18:0-CL) as compared to the synthetic 2'-deoxy analogue of cardiolipin (16:0-dCL). Such intramolecular hydrogen bonding would provide a structural basis for proton conduction on the molecular level. In aqueous dispersions at 20 degrees C, both 18:0-CL and 16:0-dCL exist in the gel phase as bilayers with gel to liquid-crystalline transitions (Tm) at 61 and 56 degrees C, respectively, whereas the unsaturated CL exists in the non-bilayer (hexagonal II) state. Evidence for intramolecular hydrogen bonding of the C-OH group in aqueous dispersions of 18:0-CL is provided by the large increase in Tm observed on changing the aqueous medium from H2O to D2O but specific hydrogen-bonded C-OH...PO2- species cannot be identified because water molecules also compete for the PO2- binding sites. However, C-OH...PO2- hydrogen bonds can be identified in dry films of the sodium salt of 18:0-CL or in CCl4 solution. In contrast, such hydrogen bonds cannot be formed in the deoxy analogue (16:0-dCL) indicating that the central C-OH group in 18:0-CL could provide a structural basis for proton conduction, involving the phosphate groups.