Trafficking and Activation of Henipavirus, Parahenipavirus, and Henipa-like Virus Fusion Proteins

Abstract

Henipaviruses are emerging zoonotic viruses that have caused deadly outbreaks in humans and livestock across several regions of the world. The fusion (F) protein of henipaviruses plays a critical role in viral entry into host cells and represents a key determinant of viral pathogenicity. This review provides a comprehensive analysis of current knowledge regarding trafficking, activation, as well as the role in particle assembly, of henipavirus F proteins. We discuss the unique characteristics of henipavirus F proteins compared to other paramyxovirus fusion proteins, with particular emphasis on their distinctive trafficking and activation mechanisms. Attention is also given to novel henipaviruses that have been detected in hosts other than bats, namely rodents and shrews. These viruses are sufficiently different that the International Committee on Taxonomy of Viruses has proposed a new genus for them, the Parahenipaviruses. We discuss how variations in F protein characteristics between Henipaviruses, Parahenipaviruses, and yet-unclassified henipa-like viruses might influence their trafficking and activation. Understanding these molecular mechanisms is crucial for developing effective therapeutic strategies against henipavirus infections and for predicting the emergence of novel henipavirus strains with pandemic potential.

Keywords: cedar virus; hendra virus; nipah virus; paramyxovirus; viral entry; zoonotic diseases.

Figure 1

Schematic of Henipavirus particle and fusion protein. (a) The nucleocapsid (N) protein (black lines) encapsidates the negative-sense, single-stranded RNA genome. The RNA-dependent RNA polymerase (L, black dot) and phosphoprotein tetramers (P, yellow shapes) complete the replication complex. The matrix protein (M, green oblongs) interacts with the cytoplasmic tails of the fusion proteins (F, red or green trimers) and of the attachment proteins (G, blue tetramers) as well as with the N protein to direct particle assembly. Green trimers represent F proteins that have not been proteolytically processed while red trimers represent processed fusion-competent F proteins. (b) The henipavirus F protein is synthesized as an inactive precursor, which is cleaved into two disulfide bond-linked fragments, F₁ and F₂. This cleavage exposes a hydrophobic fusion peptide (FP) at the N-terminus of the membrane-anchored F₁ fragment. The F₁ fragment also contains two heptad repeats (HRA and HRB) that snap together into a six-helix bundle in the post-fusion state. The cytoplasmic tail (CT) contains signals that govern F protein trafficking. TM, transmembrane.

Figure 2

Trafficking and activation of the henipavirus F protein. From bottom left: The F-trimer is transported to the plasma membrane as the precursor F₀ (green trimers, blue arrows). Upon endocytosis (purple arrows), F₀ is trafficked to Rab5⁺/4⁺ early/sorting endosomes, where it is cleaved by endosome-resident proteases into F₁₊₂ (red trimers). This fusion-competent F protein is returned to the plasma membrane via Rab11⁺-recycling endosomes. The F protein may interact with the attachment (G) protein and the matrix (M) protein at or near the plasma membrane to initiate particle assembly.

Figure 3

Phylogenetic relationships of Henipaviruses, Parahenipaviruses, and henipa-like viruses based on their F proteins. Amino acid sequences corresponding to putative F proteins were aligned using ClustalOMEGA (Version 1.2.2) [46], with the resulting phylogenetic tree generated using the Neighbor-Joining method. The optimal tree is shown. The percentage of replicate trees in which the associated taxa clustered together in the bootstrap test (1000 replicates) are shown next to the branches. GenBank accession numbers are indicated in Table 1. Viruses marked with a * have not been formally classified and are considered henipa-like viruses. Measles virus (MeV, NP_056922.1), Angavokely virus (AngV), Cedar virus (CedV), Ghana virus (GhV), Nipah virus (NiV), Hendra virus (HeV), Ninorex virus (NinExV), Chodsigoa hypsibia henipavirus (ChyV), Camp Hill virus (CHV), Resua virus (ResV), Gamak virus (GAKV), Crocidura tanakae henipavirus (CtV), Jingmen Crocidura shantungensis henipavirus 1 (JCS-1), Wufeng Crocidura attenuata henipavirus 1 (Wca-1), Shiyan Crocidura tanakae henipavirus (SCtV), Wufeng Chodsigoa smithii henipavirus 1 (WCs-1), Jingmen Crocidura shantungensis henipavirus 2 (JCS-2), Daeryong virus (DARV), Denwin virus (DewV), Melian virus (MelV), Lechcodon virus (LechV), Wenzhou shrew henipavirus 1 (WsV1), Wenzhou Apodemus agrarius henipavirus 1 (WAa-1), Hasua virus (HasV), Mojiang virus (MojV), and Langya virus (LayV).

Figure 4

Tyr-based endocytic motifs and putative endocytic signals in the HNV F cytoplasmic tail. Sequence alignment of henipavirus F-CT residues was performed using ClustalOMEGA [46]. All Tyr residues are highlighted in red. Location of canonical endocytic motifs of the form YXXØ (where X is any amino acid and Ø is an amino acid with a bulky hydrophobic sidechain) is indicated by yellow highlights. Putative, non-canonical, Tyr-based endocytic signals are indicated with a blue box. CT, cytoplasmic tail. The first charged residue, which signals the end of the transmembrane region, is indicated in bold font. Black-dash lines indicate regions lacking alignment. Bat, rodent, and shrew reservoirs are denoted by the same symbols as in Figure 3. GenBank accession numbers are indicated in Table 1. Ninorex virus (NinExV), Chodsigoa hypsibia henipavirus (ChyV), Camp Hill virus (CHV), Resua virus (ResV), Gamak virus (GAKV), Crocidura tanakae henipavirus (CtV), Jingmen Crocidura shantungensis henipavirus 1 (JCS-1), Wufeng Crocidura attenuata henipavirus 1 (Wca-1), Shiyan Crocidura tanakae henipavirus (SCtV), Wufeng Chodsigoa smithii henipavirus 1 (WCs-1), Jingmen Crocidura shantungensis henipavirus 2 (JCS-2), Daeryong virus (DARV), Denwin virus (DewV), Melian virus (MelV), Lechcodon virus (LechV), Wenzhou shrew henipavirus 1 (WsV1), Wenzhou Apodemus agrarius henipavirus 1 (WAa-1), Hasua virus (HasV), Mojiang virus (MojV), Langya virus (LayV), Angavokely virus (AngV), Cedar virus (CedV), Ghana virus (GhV), Nipah virus (NiV), and Hendra virus (HeV).

Figure 5

F1-F2 cleavage site of HeV and NiV and the predicted cleavage sites of the other Henipaviruses, Parahenipaviruses, and henipa-like viruses. Sequence alignment of HNV F protein residues was performed using ClustalOMEGA [46]. The residue after which cleavage occurs, or is predicted to occur, is indicated in red. Arrow indicates cleavage site. FP, fusion peptide. Known or predicted FP residues are indicated in bold font. GenBank accession numbers are indicated in Table 1. Ninorex virus (NinExV), Chodsigoa hypsibia henipavirus (ChyV), Camp Hill virus (CHV), Resua virus (ResV), Gamak virus (GAKV), Crocidura tanakae henipavirus (CtV), Jingmen Crocidura shantungensis henipavirus 1 (JCS-1), Wufeng Crocidura attenuata henipavirus 1 (Wca-1), Shiyan Crocidura tanakae henipavirus (SCtV), Wufeng Chodsigoa smithii henipavirus 1 (WCs-1), Jingmen Crocidura shantungensis henipavirus 2 (JCS-2), Daeryong virus (DARV), Denwin virus (DewV), Melian virus (MelV), Lechcodon virus (LechV), Wenzhou shrew henipavirus 1 (WsV1), Wenzhou Apodemus agrarius henipavirus 1 (WAa-1), Hasua virus (HasV), Mojiang virus (MojV), Langya virus (LayV), Angavokely virus (AngV), Cedar virus (CedV), Ghana virus (GhV), Nipah virus (NiV), and Hendra virus (HeV).