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Energetics of the HIV gp120-CD4 binding reaction
D G Myszka1, R W Sweet, P Hensley
1Department of Oncological Sciences, Huntsman Cancer Institute, University of Utah, Salt Lake City, UT 84112, USA. dmyszka@hci.utah.edu
Summary
The CD4-gp120 interaction in HIV involves significant structural changes in the virus's gp120 protein. This conformational flexibility may aid HIV in infection and immune evasion.
Area of Science:
- Biochemistry
- Virology
- Structural Biology
Background:
- HIV infection begins with the interaction between the cellular receptor CD4 and the viral envelope glycoprotein gp120.
- Understanding this interaction is crucial for developing antiviral therapies.
Purpose of the Study:
- To characterize the assembly state, thermodynamics, and kinetics of the CD4-gp120 interaction.
- To investigate the structural basis of CD4 binding to gp120.
Main Methods:
- Analytical ultracentrifugation
- Titration calorimetry
- Surface plasmon resonance biosensor analysis
- Circular dichroism (CD) spectral studies
Main Results:
- The binding thermodynamics of CD4-gp120 interaction were unexpectedly large, exceeding typical protein-protein interactions.
- Extensive structural rearrangements within the gp120 core occur upon CD4 binding, indicated by large changes in heat capacity and entropy.
- CD spectral studies and slow binding kinetics support significant conformational changes in gp120.
Conclusions:
- gp120 exhibits considerable conformational flexibility upon binding to CD4.
- This flexibility may play a role in HIV's ability to trigger infection.
- Conformational flexibility might also contribute to HIV's mechanism of evading the immune system by masking conserved receptor-binding sites.