This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Microbiology
True about Shiga toxin ? 
Select and explain. 
A. An endotoxin, B. Inhibit protein synthesis, C. Activate adenylyl cyclase, D. Increase cGMP
B: Inhibit protein synthesis
Answer: B: Inhibit protein synthesis 
Explanation: Ans. is 'b' i.e., Inhibit protein synthesis Shiga toxin (verocytotoxin) It is an exotoxin. It is produced by shigella dysentriae type 1. Genes encoding shiga toxin are located on chromosome, while the VT1 of EHEC is phage-encoded. Toxin constits of two subunits - b Subunits, helps is binding and A subunit which has the active poion of toxin. Subunit 'A' is divided into A, and A2 fragment. A l fragments inhibits protein synthesis by inactivating 60s ribosome.