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The lateral diffusion of selectively aggregated peptides in giant unilamellar vesicles
Clarence C Lee1, Matthew Revington, Stanley D Dunn
1Department of Chemistry, The University of Western Ontario, London, Canada.
Abstract:
We have systematically investigated the effect of aggregation of a transmembrane peptide on its diffusion in dimyristoylphosphatidylcholine and in palmitoyloleoylphosphatidylcholine model membranes. The hydrophobic segment of the b subunit from E. coli F(1)F(0)-ATP synthase was modified with a histidine tag at the carbonyl terminus and was aggregated selectively by using a series of multivalent, dendritic chelating agents with nitrilotriacetic acid functional groups. Peptide complexes ranging from monomers to hexamers were formed and studied in giant unilamellar vesicles. The rate of diffusion for the transmembrane peptide complexes were found to depend on the size of the complex. The results agree with predictions from the free area model for monomers and dimers, and the hydrodynamic continuum model for tetramers, pentamers, and hexamers. Comparisons with diffusion of lipids confirm that the diffusion of a transmembrane peptide is enhanced by coupling of density fluctuations between the two monolayers.
Insights
Transmembrane peptide aggregation affects diffusion in model membranes. Larger complexes diffuse slower, aligning with free area and hydrodynamic models, and showing enhanced diffusion due to monolayer coupling.
Area of Science:
- Biophysics
- Membrane protein dynamics
- Biochemistry
Background:
- Transmembrane peptides play crucial roles in cellular functions.
- Understanding their diffusion is key to elucidating membrane protein behavior.
- Aggregation significantly impacts molecular mobility within lipid bilayers.
Purpose of the Study:
- To investigate how the aggregation state of a transmembrane peptide influences its diffusion rate.
- To analyze the diffusion of peptide complexes (monomers to hexamers) in different model membranes.
- To compare experimental findings with theoretical models of molecular diffusion.
Main Methods:
- Systematic aggregation of a modified E. coli F(1)F(0)-ATP synthase b subunit peptide using dendritic chelating agents.
- Formation of peptide complexes ranging from monomers to hexamers.
- Diffusion studies in giant unilamellar vesicles composed of dimyristoylphosphatidylcholine and palmitoyloleoylphosphatidylcholine.
- Comparison with lipid diffusion rates.
Main Results:
- Diffusion rate of transmembrane peptide complexes is dependent on their size (aggregation state).
- Experimental data for monomers and dimers align with the free area model.
- Data for tetramers, pentamers, and hexamers are consistent with the hydrodynamic continuum model.
- Enhanced diffusion was observed, attributed to coupling of density fluctuations between lipid monolayers.
Conclusions:
- Peptide aggregation state is a critical determinant of its membrane diffusion dynamics.
- The study validates the applicability of different theoretical models across various aggregation states.
- Coupling of density fluctuations between lipid monolayers enhances transmembrane peptide diffusion.