Cryo-EM structure of the prefusion state of canine distemper virus fusion protein ectodomain
David Kalbermatter1, Neeta Shrestha2,3, Flavio M Gall4
1Institute of Biochemistry and Molecular Medicine, University of Bern, Bern, Switzerland.
Abstract:
Measles virus (MeV) and canine distemper virus (CDV), two members of the Morbillivirus genus, are still causing important global diseases of humans and animals, respectively. To enter target cells, morbilliviruses rely on an envelope-anchored machinery, which is composed of two interacting glycoproteins: a tetrameric receptor binding (H) protein and a trimeric fusion (F) protein. To execute membrane fusion, the F protein initially adopts a metastable, prefusion state that refolds into a highly stable postfusion conformation as the result of a finely coordinated activation process mediated by the H protein. Here, we employed cryo-electron microscopy (cryo-EM) and single particle reconstruction to elucidate the structure of the prefusion state of the CDV F protein ectodomain (solF) at 4.3 Å resolution. Stabilization of the prefusion solF trimer was achieved by fusing the GCNt trimerization sequence at the C-terminal protein region, and expressing and purifying the recombinant protein in the presence of a morbilliviral fusion inhibitor class compound. The three-dimensional cryo-EM map of prefusion CDV solF in complex with the inhibitor clearly shows density for the ligand at the protein binding site suggesting common mechanisms of membrane fusion activation and inhibition employed by different morbillivirus members.
Insights
Researchers visualized the canine distemper virus fusion protein in its prefusion state. This structural insight into morbillivirus fusion mechanisms could aid in developing new antiviral therapies.
Area of Science:
- Structural biology
- Virology
- Molecular mechanisms of viral entry
Background:
- Measles virus (MeV) and canine distemper virus (CDV) are significant morbilliviruses causing diseases in humans and animals.
- Morbillivirus cell entry depends on the interaction between the H (hemagglutinin) and F (fusion) glycoproteins.
- The F protein transitions from a metastable prefusion state to a stable postfusion state to mediate membrane fusion.
Purpose of the Study:
- To determine the high-resolution structure of the canine distemper virus (CDV) F protein ectodomain (solF) in its prefusion state.
- To understand the structural basis of morbillivirus fusion and identify potential targets for antiviral intervention.
Main Methods:
- Cryo-electron microscopy (cryo-EM) and single particle reconstruction were used to analyze the prefusion CDV F protein.
- The prefusion state was stabilized using a GCNt trimerization sequence and a morbilliviral fusion inhibitor.
Main Results:
- A 4.3 Å resolution cryo-EM map of the prefusion CDV solF trimer was obtained.
- The structure revealed the ligand binding site of the inhibitor, suggesting conserved fusion mechanisms across morbilliviruses.
- Density for the inhibitor was observed within the protein binding site.
Conclusions:
- The study provides the first structural elucidation of the prefusion state of the CDV F protein.
- The findings suggest conserved mechanisms for membrane fusion activation and inhibition among morbilliviruses.
- This structural information is valuable for the design of novel antiviral drugs targeting morbillivirus entry.
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