Factor D Protein: Covid-19

Why in News

A new study by Johns Hopkins Medicine researchers suggests that blocking a human protein factor D may curtail the potentially deadly inflammatory reactions that many patients have to the novel coronavirus (SARS-CoV-2).

Key Points

  • Method: The new study used normal human blood serum and three subunits of the SARS-CoV-2 spike protein to discover exactly how the virus hijacks the immune system and endangers normal cells.
  • Focus: Team focused on two proteins, factor H and factor D, which are known as “complement” proteins, because they help the immune system clear pathogens from the body.
  • Findings: The researchers discovered that Covid-19’s spike protein causes factor D to overstimulate the immune response, which in turn prevents factor H from mediating that response.
    • Spike proteins on the surface of SARS-CoV-2 are the means by which it attaches to cells targeted for infection.
    • The spikes first grab hold of a molecule called heparan sulfate.
      • Heparan sulfate is a large, complex sugar molecule found on the surface of cells in the lungs, blood vessels and smooth muscle making up most organs.
    • Facilitated by its initial binding with heparan sulfate, SARS-CoV-2 then uses another cell-surface component, the protein known as angiotensin-converting enzyme 2 (ACE2), as its doorway into the attacked cell.
      • ACE2 is a protein on the surface of many cell types.
      • It is an enzyme that generates small proteins – by cutting up the larger protein angiotensinogen – that then go on to regulate functions in the cell.
    • When SARS-CoV-2 attacks the ACE2 receptors to proliferate and infect more cells in the human body, it also prevents Factor H from using the sugar molecule to bind with cells.
      • Factor H’s main function is to regulate the chemical signals that trigger inflammation and keep the immune system from harming healthy cells.
    • The team found that by blocking factor D, they were able to stop the destructive chain of events triggered by SARS-CoV-2.
  • Significance:
    • It has provided a definite direction for research to tackle Covid-19.
    • There may already be drugs in development for other diseases that can block this protein, a positive sign for the study.

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