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How does the virus invade cleverly? Uncover the secret of the fusion of HIV and cells!
In today's world, some viruses are causing global health challenges, the most well-known of which is human immunodeficiency virus (HIV). The ingenious and complex intrusion process of this virus deserves our in-depth exploration.
A fusion mechanism is any method by which a cell or virus fuses with a cell, and the mechanical facilities for these processes enable it to proceed.
In the process of cell fusion, two separate cells first need to be fused into a hybrid cell. Whether it is virus-cell fusion or cell-to-cell fusion, it covers three main processes: dehydration of polar groups, promotion of half-fusion, and opening and expansion of pores between different cells.
Key steps in virus-cell fusion
Take HIV as an example. The virus enters host cells mainly by fusing the immune cell membrane of the infected object. For successful fusion, HIV must bind to receptors such as CD4, CCR5, and CXCR4. This process not only involves the proteins of the virus itself, but also explains the basic principles of membrane fusion.
Scientists have discovered that the structure and properties of viral fusion proteins are crucial for membrane fusion.
The role of fusion proteins (Fusogens)
In the fusion process of viruses and cells, fusion proteins play an important role. These proteins help overcome barriers to membrane fusion. In particular, scientists divide these fusion proteins into four categories:
Class I fusion protein
This type of fusion protein consists of three subunits, and before fusion, the fusion loop is hidden within its structure. After fusion, its structure will refold to form a new trimer structure. Both HIV and influenza virus fusion depend on such proteins.
Class II fusion protein
This type of fusion protein is also composed of three subunits and contains multiple β-pleated sheets, which can change its conformation in an acidic environment and participate in inserting the fusion ring into the target membrane.
Class III fusion protein
The structure of this type of fusion protein contains both α-helices and β-sheets and also plays an important role in the cell fusion process.
Class IV fusion protein
Although this type of fusion protein does not participate in traditional virus-cell fusion, when they are expressed on the cell surface, they can induce fusion between cells.
Mechanism of cell fusion
During the fusion process of mammalian cells, there are usually five main stages:
1. Set fusion ability
Cells must adjust the composition of their membranes to give them the ability to fuse. This requires protein synthesis and removes obstacles to the fusion process.
2. Chemotaxis
Cells attract each other through signaling molecules to pair up. For example, sperm cells are attracted to eggs through hormonal signals.
3. Membrane adhesion
When cells come into contact, they establish connections through cell recognition mechanisms, which is also a necessary step before fusion.
4. Membrane fusion
This step drives the mixing of cell contents, mainly regulated by fusion proteins, forming fusion pores to allow internal communication.
5. Reset after fusion
After fusion is complete, the cell's fusion machinery needs to be disassembled to prevent further unnecessary fusion.
Therapeutic Potential
Exploring the application of fusion mechanisms has also become a research direction for emerging therapies. For example, certain viral glycoproteins lose their fusion ability in the presence of NMT inhibitors, which may serve as a therapeutic strategy against hemorrhagic viruses.
The fusion process is so complex and exquisite. How do these viruses find their target cells and complete their invasion?
