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Fragmentation of dimyristoylphosphatidylcholine vesicles by apomyoglobin
1Department of Life Science, Korea Advanced Institute of Science and Technology, Taejon.
Abstract:
Previously we have reported results of a preliminary study on the micellization of phosphatidylcholine vesicles by apomyoglobin at pH 4 (J. W. Lee and H. Kim, 1988, FEBS Lett. 241, 181-184). The micellization study has been extended here to investigate the effect of the lipid to protein ratio, temperature, size of vesicles, and pH. The pH-dependent study indicated that micellization occurs when the protein assumes either a molten globular or random coil structure. Time-dependent hydrophobic labeling by 3-(trifluoromethyl)-3-(m-[125I]iodophenyl)-diazirine showed that there is an initial increase in contact between the protein and hydrophobic acyl chain of lipid followed by a decrease in the interaction. This may be explained as the initial stage of vesicle aggregation which is subsequently superseded by the fragmentation. These reactions are discussed in term of protein unfolding at low pH.
Insights
Apomyoglobin protein causes phosphatidylcholine vesicles to form micelles, especially at low pH when the protein unfolds. This interaction changes over time, suggesting initial aggregation followed by fragmentation.
Area of Science:
- Biochemistry
- Biophysics
- Protein-lipid interactions
Background:
- Previous research established apomyoglobin's ability to micellize phosphatidylcholine vesicles at pH 4.
- Further investigation is needed to understand the factors influencing this process.
Purpose of the Study:
- To extend the micellization study by examining the effects of lipid-to-protein ratio, temperature, vesicle size, and pH.
- To elucidate the mechanism of protein-induced vesicle aggregation and fragmentation.
Main Methods:
- Investigated micellization across varying lipid-to-protein ratios, temperatures, vesicle sizes, and pH conditions.
- Utilized time-dependent hydrophobic labeling with 3-(trifluoromethyl)-3-(m-[125I]iodophenyl)-diazirine.
- Analyzed protein structure changes (molten globular, random coil) in relation to pH.
Main Results:
- Micellization was observed when apomyoglobin adopted molten globular or random coil structures, particularly at low pH.
- Hydrophobic labeling revealed an initial increase in protein-lipid contact, followed by a decrease.
- The observed changes suggest a process of vesicle aggregation followed by fragmentation.
Conclusions:
- Protein unfolding at low pH is critical for apomyoglobin-induced phosphatidylcholine vesicle micellization.
- The dynamic changes in protein-lipid interaction indicate a complex mechanism involving aggregation and fragmentation.
- These findings contribute to understanding protein-lipid interactions and their structural consequences.