Measles Virus And Hemagglutinin Protein

Introduction to MeV

MeV is a paramyxovirus with a non-segmented RNA genome that encodes various proteins, including nucleocapsid protein (NP), virulence factors (C and V), phosphoprotein (P), matrix protein (M), hemagglutinin (H), membrane fusion protein (F), and RNA-dependent RNA polymerase (L). MeV is enveloped and contains two viral glycoproteins, H and F, on its membrane. The H and F proteins form a hetero-oligomer that is essential for inducing membrane fusion. Upon binding to its receptor, the H protein undergoes a conformational change, leading to a structural rearrangement of the F protein. This rearrangement occurs from the metastable pre-fusion form to the intermediate and post-fusion forms. These changes facilitate the fusion of the viral envelope with the host cell membrane, allowing the virus to enter the cell. During this process, the binding of H protein to cell receptors is the initial event of infection. The attachment of H to its host receptor triggers the fusion of the F protein between the virus and the host cell membrane.

Interaction between H Protein and MeV Receptors

MeV receptors play a critical role in the viral entry process, allowing the virus to attach to and enter host cells. Three protein molecules have been identified as MeV receptors, CD46, the signaling lymphocyte activation molecule (SLAM), and nectin-4.

• CD46
  CD46 is a widely expressed cellular receptor that serves as a regulator of complement activation. It is involved in various physiological processes, including immune regulation and tissue homeostasis. Certain strains of MeV, particularly vaccine strains and laboratory-adapted strains, can utilize CD46 as a receptor for viral entry.
  The interaction between MeV hemagglutinin (H) protein and CD46 is mediated by specific binding sites on both molecules. This interaction triggers the fusion of the viral envelope with the host cell membrane, facilitating viral entry. CD46 is found on the surface of nucleated human cells, allowing MeV to infect a broad range of cell types.
• SLAM
  SLAM, also known as CD150, is a cell surface receptor primarily expressed on immune cells, including B cells, T cells, dendritic cells, and macrophages. SLAM is the primary receptor used by wild-type MeV strains for entry into host cells.
  The binding of the MeV H protein to SLAM initiates a series of events leading to viral entry. This interaction triggers membrane fusion and the release of the MeV genome into the host cell, ultimately leading to viral replication and spread. The tropism of MeV for immune cells is largely attributed to its reliance on the SLAM receptor.
• Nectin-4
  Nectin-4, also known as poliovirus receptor-related 4 (PVRL4), is a cell adhesion molecule belonging to the nectin family. It is expressed at high levels in the respiratory epithelium and is involved in cell-to-cell adhesion. Nectin-4 has emerged as an alternative receptor for MeV entry, particularly in certain types of human cancer.
  In cancer cells, MeV can exploit the presence of nectin-4 to gain entry into the cells. The interaction between the MeV H protein and nectin-4 allows the virus to infect and replicate within cancer cells, potentially offering a novel approach for oncolytic virotherapy.

It's important to note that the usage of these receptors by MeV can vary depending on the viral strain, viral adaptation, and cell type. The receptor repertoire of MeV highlights its ability to infect a wide range of cell types, contributing to the systemic and respiratory manifestations observed in measles infections.

Understanding the specific interactions between MeV and its receptors, including CD46, SLAM, and nectin-4, provides insights into viral tropism, pathogenesis, and potential targets for therapeutic interventions and vaccine development. Ongoing research continues to explore the intricate details of MeV receptor usage to enhance our understanding of this viral infection.