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Structural characterization of peptide fragments from hCD81-LEL
M Dhanasekaran1, P W Baures, S VanCompernolle
1Department of Chemistry, Kansas State University, USA.
Summary
Two peptides from human CD81 (hCD81) large extra-cellular loop (LEL) show helical structures in TFE, influenced by pH and salt. Peptide 1 blocks hepatitis C virus glycoprotein E2 (HCV-E2) binding at high concentrations.
Area of Science:
- Biochemistry
- Structural Biology
- Virology
Background:
- The large extra-cellular loop (LEL) of human CD81 (hCD81) is crucial for binding hepatitis C virus glycoprotein E2 (HCV-E2).
- Understanding the structural dynamics of hCD81 LEL peptides is key to elucidating HCV-E2 interaction mechanisms.
Purpose of the Study:
- To characterize the solution conformation of two hCD81 LEL peptides.
- To determine the solution structure of a critical peptide (Peptide 1) involved in HCV-E2 binding.
- To investigate the influence of environmental factors (TFE, pH, NaCl) on peptide structure.
Main Methods:
- Circular dichroism (CD) spectroscopy to assess secondary structure.
- 1D and 2D proton nuclear magnetic resonance (1H NMR) spectroscopy for detailed structure determination.
- Cell-based assays to evaluate peptide inhibition of rHCV-E2 binding to hCD81.
Main Results:
- Both peptides were unstructured in water but adopted significant alpha-helical conformations in 20% or higher trifluoroethanol (TFE).
- CD data indicated that electrostatic forces (pH and NaCl concentration) stabilize the helical structure of both peptides.
- Peptide 1 inhibited recombinant HCV-E2 (rHCV-E2) binding to hCD81 on Molt-4 T cells at high concentrations (3.5 mM), suggesting low binding affinity in aqueous solution.
Conclusions:
- The structural behavior of hCD81 LEL peptides in solution is influenced by solvent composition and ionic strength.
- The observed helical propensity in TFE aligns with their native conformation within the protein.
- Peptide 1's ability to block HCV-E2 binding, despite its disordered state in water, highlights the complexity of protein-peptide interactions in viral entry.