McrBC Molecular scissiors

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GS-3 Science and Technology
GS-2 Issues relating to health
GS-4 Medical Ethics 


IISER has determined the atomic structure of McrBC- a complex bacterial protein that helps prevent viral infections in bacterial cells as molecular scissors. 


Working with molecular scissors. A high- resolution structure of McrBC was possible by using electron cryomicroscopy, commonly known as cryo-EM. 

Phage Therapy

  • The determination of the McrBC’s structure has long-term implications in ‘phage therapy’ and could help combat drug-resistant infections in the future. 
  • The practice of phage therapy uses bacterial viruses (phages) to treat bacterial infections. 
  • Phages are groups of viruses that infect and kill bacterial cells and phage therapy is the therapeutic use of bacteriophages to treat bacterial infections.
  • Understanding of the molecular scissors would aid in combating multidrug-resistant microbes. 

How the molecular scissors in bacteria work?

  • Like humans, bacteria to have an elaborate defense system to combat phages or the viruses which infect bacterial cells. 
  • These phages inject their DNA into the bacterial cell, wherein they multiply and duplicate the virus that eventually bursts out of that cell to infect many more.
  • So to prevent infection, bacteria have specialized ‘molecular scissors’ which specifically cut the foreign DNA, thereby preventing their multiplication in bacterial cells. 
  • The molecular scissors of bacteria also regulate the entry of other foreign DNA that might host an antibiotic resistance gene. 

Features of McrBC 

  • To cut the foreign DNA, McrBC is powered by an inbuilt motor that uses GTP (guanosine triphosphate) is the energy currency of the bacterial cell. 
  • The atomic structure of McrBC (by using cryo-EM) reveals the details of its working parts. McrBC is used as a laboratory tool to study the readability of human and other genomes. 

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