Acidic pH Triggers Lipid Mixing Mediated by Lassa Virus GP

Area of Science:

• Virology
• Molecular Biology
• Biochemistry

Background:

• Lassa virus (LASV) causes Lassa hemorrhagic fever, a significant public health concern in West Africa.
• LASV entry into host cells is mediated by its envelope glycoprotein (GP), a class I membrane fusogen and the virus's only surface antigen.
• Previous research identified cellular receptors and endosomal acidification as crucial for LASV infection.

Purpose of the Study:

• To investigate the conformational changes in LASV GP triggered by physiological endosomal conditions.
• To directly visualize and characterize the LASV GP-mediated fusion process using a single-particle assay.
• To elucidate the role of lysosomal-associated membrane protein 1 (LAMP1) in LASV fusion kinetics.

Main Methods:

• Incubation of LASV pseudovirions at physiological late endosome temperature and pH to assess infectivity and GP conformation via antibody binding.
• Development and application of a single-particle fluorescence assay to observe LASV GP-mediated lipid mixing with supported planar bilayers.
• Quantification of lipid mixing kinetics in the presence and absence of cellular receptors, specifically LAMP1, under varying pH conditions.

Main Results:

• Incubation at physiological late endosome temperature and pH inactivates LASV pseudovirions, correlating with GP conformational changes.
• Direct visualization confirmed that endosomal pH and physiological temperature are sufficient to trigger LASV GP-mediated lipid mixing.
• While not essential for triggering lipid mixing, LAMP1 significantly increased the kinetics of fusion at endosomal pH and enabled robust lipid mixing under less acidic conditions.

Conclusions:

• LASV GP undergoes functionally relevant conformational changes at physiological endosomal conditions, leading to membrane fusion.
• LAMP1 plays a crucial role in enhancing LASV fusion kinetics and efficiency, particularly under mildly acidic endosomal environments.
• These findings provide critical insights into the molecular mechanisms of LASV entry and the host-pathogen interactions involving LAMP1.