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The membrane insertion of trichosanthin is membrane-surface-pH dependent
1State Key Laboratory of Biomembranes, Department of Biological Sciences and Biotechnology, Tsinghua University, Beijing 100084, People's Republic of China.
The Biochemical Journal
|July 21, 2000
Summary
Trichosanthin (TCS), a protein from traditional Chinese medicine, inserts into cell membranes at low pH. This pH-dependent conformational change exposes hydrophobic sites, enabling its ribosome-inactivating function.
Area of Science:
- Biochemistry
- Molecular Biology
- Pharmacology
Background:
- Trichosanthin (TCS) is a type-I ribosome-inactivating protein (RIP) from the traditional Chinese herb Tianhuafen.
- TCS exhibits immunomodulatory, anti-tumour, and anti-HIV activities, with membrane insertion crucial for its function.
- Understanding TCS's membrane-insertion mechanism is key to its therapeutic applications.
Purpose of the Study:
- To elucidate the mechanism of membrane insertion for Trichosanthin (TCS).
- To investigate the role of pH in TCS membrane interaction and conformational changes.
Main Methods:
- Monolayer experiments to assess membrane-insertion ability.
- Fluorescence spectroscopy with 1-anilinonaphthalene-8-sulphonic acid probe.
- Circular Dichroism (CD) spectroscopy to analyze secondary structure changes.
Main Results:
- TCS membrane insertion is dependent on low pH.
- Low pH induces a conformational change in TCS, exposing hydrophobic sites without altering secondary structure.
- This conformational change leads to a molten globular state, facilitating membrane interaction.
Conclusions:
- A pH-dependent mechanism for TCS membrane insertion is proposed.
- The conformational change at low pH is critical for TCS to enter the cytoplasm and exert its RIP activity.
- This study provides insights into the structure-function relationship of TCS for potential therapeutic development.