This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Bacteria, Subject name: Microbiology
[{'content': 'Mechanism of action of pertussis toxin is all except: \nSelect and explain. \nA. Act by ADP ribosylation of GI subunit, B. Increase in calcium, C. Act by decreasing GTP, D. B subunit having ADP ribosylating activity', 'role': 'user'}, {'content': "Answer: A \nExplanation: Ans. is 'a' i.e., Act by ADP ribosylation of GI subunitRef: (Harrison, 19th/e, p. 1021 and Ananthanarayan, 9th/e, p. 333)Pertussis toxin (PT) - Most imp. Virulence factor composed of 2 subunits (A and B) like cholera toxin. A subunit having ADP ribosylation activity of G protein - | cAMP - responsible for several biological effects like T cell mitogeni- city, Hemagglutination, Adhesion to respiratory ciliated cells, induction of leukocytosis, histamine sensitizer.", 'role': 'assistant'}]