Question

Describe the mode of action for AB toxins and why they are typically host-specific. ( explain briefly )

Answer 1

Answer :- The AB toxins are two-component protein complexes secreted by a number of pathogenic bacteria.

1. A portion is a toxic protein portion. which constitute the enzyme which is toxic to cell. The enzyme component (A) enters the cell through endosomes produced by the oligomeric binding/translocation protein (B), and prevents actin polymerisation through ADP-ribosylation of monomeric G-actin.

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2.B portion helps the attachment on the host cell receptor. It removed by host cell by the process of exocytosis

Eg - Botulinum toxins are members of a broad class of bacterial toxic proteins, called AB toxins. ... Other AB toxins include tetanus, cholera, anthrax, shiga and diphtheria toxins.

The mode of action of AB toxins –

1.The B portion is attached on the cell receptor.

2.The host cell engulf the AB toxin through the endocytosis. And a vesicle is formed and move into the cytoplasm.

3.In side the vesicle the AB particles separated. The A protein portion is released in to cytoplasm , which exert a toxic effect on host cell.

4.The Remaining B portion is removed from the cell through the process of exocytosis.

5.The A enzyme [toxin] attached to the elongation factor 2 [translation protein] and stop the translation processes and inhibit the protein synthesis.

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6.Eg :- the Cholera AB toxin attached on the GM receptor of intestinal cell membrane. The A protein is made up of two domain A1 domain[toxic] and A2 domain [attached to B portion] attached with each other by disulphide bond . The enzyme protease breaks these two domains. The AB is entered into cell by endocytosis , and entered into endoplasmic reticulum . A1 is released by A2 into the cytoplasm . A1 act on the cell and stop the protein synthesis process.