The Nanoscale Organization of the Nipah Virus Fusion Protein Reveals Novel Insights into Membrane Fusion Mechanisms

Core Concepts

The nanoscale organization of the Nipah virus fusion protein on biological membranes is critical for its membrane fusion activity, and is regulated by interactions with endocytosis components.

Abstract

The study used single-molecule localization microscopy to investigate the nanoscale organization of the Nipah virus fusion protein (NiV-F) on cell and virus-like particle membranes. The key findings are:

NiV-F forms regular-sized nanoclusters on biological membranes, independent of its expression level or endosomal cleavage. The estimated size of the NiV-F clusters is similar to the hexamer-of-trimer assembly observed in the crystal structure of the soluble NiV-F ectodomain.

Mutations that destabilize the hexameric interface of NiV-F lead to more dispersed and smaller clusters, while a mutation that stabilizes the hexameric interface promotes clustering. This suggests the NiV-F nanoclusters are likely hexamer-of-trimer assemblies on membranes.

NiV-F molecules sequestered in nanoclusters favor membrane fusion activation, indicating the spatial organization of NiV-F is important for its function.

The interactions between NiV-F, the endocytosis adaptor complex AP-2, and the clathrin coat stabilize the NiV-F nanoclusters on the cell membrane. Disrupting these interactions leads to more dispersed NiV-F distribution.

The authors propose that the NiV-F nanoclusters are the fundamental unit of the Nipah virus fusion machinery, and this organization facilitates membrane fusion triggering by a mixed population of NiV-F molecules with varied degrees of cleavage and opportunities for interacting with the NiV-G/receptor complex.

Stats

The cell surface expression levels of NiV-F constructs are comparable.
The fusion activity of FLAG-tagged NiV-F mutants is similar to their untagged counterparts.
The cleavage efficiency of the NiV-F mutants varies, with L53D being the least efficiently cleaved.

Quotes

"NiV-F forms regular-sized nanoclusters on biological membranes regardless of the expression level or endosomal cleavage."
"The nano-organization of NiV-F reveals the fundamental unit of NiV fusion machinery."
"The interactions among NiV-F, the AP-2 complex, and the clathrin coat assembly stabilize the NiV-F clusters."

Key Insights Distilled From

The nanoscale organization of the Nipah virus fusion protein informs new membrane fusion mechanisms

by Wang,Q., Liu... at www.biorxiv.org 02-08-2024

https://www.biorxiv.org/content/10.1101/2024.02.07.579372v1

Deeper Inquiries

How do the NiV-F nanoclusters reorganize upon triggering by the NiV-G/receptor complex on live cell membranes

Upon triggering by the NiV-G/receptor complex on live cell membranes, the NiV-F nanoclusters likely reorganize by facilitating interactions between adjacent F molecules at the edge of the clusters. This reorganization allows the fusion-active NiV-F molecules to initiate conformational changes and merge with the opposing membranes. The triggered, fusion-active NiV-F at the cluster periphery may act as a catalyst for other F molecules within the cluster, maximizing the energy required for membrane fusion. The transient interactions between the F molecules and the NiV-G/receptor complex likely play a crucial role in coordinating the fusion process.

What is the minimum number of NiV-F molecules required within a nanocluster to facilitate membrane fusion activation

The minimum number of NiV-F molecules required within a nanocluster to facilitate membrane fusion activation is not definitively established in the current research. However, based on the observations that NiV-F nanoclusters are favorable for membrane fusion activation and that a mixed population of NiV-F molecules within a cluster can contribute to fusion pore formation, it can be inferred that a collaborative effort of multiple copies of NiV-F is necessary to overcome the energy barrier for membrane fusion. Further studies focusing on quantifying the exact number of NiV-F molecules within a nanocluster and their specific roles in fusion activation would provide more insights into this aspect.

How do the host factors that maintain the NiV-F nanoclusters represent potential therapeutic targets for Nipah virus infections

Host factors that maintain the NiV-F nanoclusters, such as the endocytosis components AP-2 and the clathrin coat assembly, represent potential therapeutic targets for Nipah virus infections. Disrupting the interactions between NiV-F and these host factors could potentially destabilize the F clusters, making the virus less efficient in membrane fusion and cell entry. Targeting the mechanisms that stabilize the NiV-F nanoclusters could hinder the fusion process and reduce viral infectivity. Developing inhibitors that specifically interfere with these interactions could offer a novel approach to combating Nipah virus infections and may lead to the development of new antiviral therapies.