Structural and Mechanistic Evidence for Calcium Interacting Sites in the HIV Transmembrane Protein gp41 Involved in...

Area of Science:

• Virology
• Structural Biology
• Biochemistry

Background:

• HIV entry relies on the gp41 protein's conformational change to form a six-helix bundle (SHB).
• The interaction between gp41's heptad repeat regions (CHR and NHR) forms the SHB, a target for peptide inhibitors.
• Existing fusion inhibitors like T20 are crucial for managing HIV infection.

Purpose of the Study:

• To identify and characterize calcium interaction motifs (CIMs) within the gp41 protein.
• To investigate the role of calcium ions in the assembly of the gp41 CHR-NHR six-helix bundle.
• To assess the impact of calcium and CIMs on the efficacy of gp41-derived fusion inhibitors.

Main Methods:

• Nuclear Magnetic Resonance (NMR) spectroscopy was employed to detect CIMs.
• Mutagenesis studies were conducted to assess the function of CIMs.
• Fusion inhibition assays were performed in the presence and absence of calcium.

Main Results:

• Calcium interaction motifs (CIMs) were identified in both CHR and NHR regions of gp41.
• SHB assembly is enhanced by Ca²⁺ and impaired in CIM mutants.
• The fusion inhibitor T20 showed reduced efficacy in calcium-containing environments.

Conclusions:

• Calcium ions play a significant role in facilitating gp41 SHB formation.
• CIMs are critical for efficient gp41-mediated membrane fusion.
• Findings suggest potential for developing improved HIV fusion inhibitors by considering calcium's influence.