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The structure and function of gramicidin A embedded in interdigitated bilayer
1National Laboratory of Biomacromolecules, Institute of Biophysics, Academia Sinica, Beijing, People's Republic of China.
Insights
Phase transition to interdigitated lipid bilayers significantly alters membrane protein function and structure. Gramicidin A showed reduced K+ transport and altered conformation in interdigitated bilayers, indicating a more hydrophobic environment.
Area of Science:
- Biophysics
- Membrane Biology
- Protein Structure
Background:
- Membrane proteins are crucial for cellular functions.
- Lipid bilayer structure influences protein activity.
- Phase transitions in lipid bilayers can alter the membrane environment.
Purpose of the Study:
- To investigate the impact of lipid bilayer phase transitions on membrane protein function and structure.
- To model these effects using linear gramicidin (gramicidin A).
Main Methods:
- Induction of interdigitated dipalmitoylphosphatidylglycerol (DPPG) liposomes using atropine.
- Assaying K+ transport via gramicidin using membrane potential measurements.
- Analyzing gramicidin's environment using intrinsic fluorescence spectroscopy.
- Determining gramicidin's conformation with circular dichroism (CD) spectroscopy.
Main Results:
- Gramicidin's K+ transport capability was reduced in interdigitated bilayers compared to normal bilayers.
- Intrinsic fluorescence indicated a more hydrophobic environment for gramicidin in interdigitated bilayers.
- CD measurements revealed that gramicidin's conformation deviated from the typical beta6.3 helix in interdigitated bilayers.
Conclusions:
- Interdigitated lipid bilayers significantly affect membrane protein function, specifically reducing ion transport.
- The altered hydrophobic environment and conformational changes in gramicidin highlight the structural impact of interdigitation.
- These findings suggest that lipid bilayer phase state is a critical determinant of membrane protein behavior.
Abstract:
The effects of phase transition from normal to interdigitated lipid bilayer on the function and structure of membrane proteins were studied using linear gramicidin (gramicidin A) as a model. Interdigitated bilayer structure of dipalmitoylphosphatidylglycerol (DPPG) liposomes that was induced by atropine could not be changed notably by intercalating of gramicidin. The K+ transportation of gramicidin in both normal and interdigitated bilayer was assayed by measuring the membrane potential. Results showed that gramicidin in interdigitated bilayer exhibited lower transport capability. Intrinsic fluorescence spectrum of gramicidin in interdigitated bilayer blue-shifted 2.8 nm from the spectrum in normal bilayer, which means that interdigitation provides a more hydrophobic environment for gramicidin. Circular dichroism measurement results indicated that the conformation of gramicidin in interdigitated bilayer is not the typical beta6.3 helix as in the normal bilayer. The results suggested that the interdigitated lipid bilayer might largely affect the structure and function of membrane proteins.