Which molecular mechanism underlies the action of diphtheria toxin on host cells?

• A Cleavage of SNARE proteins at the neuromuscular junction
• B ADP-ribosylation of Gs protein, causing unregulated adenylate cyclase activity
• C ADP-ribosylation of elongation factor 2, halting protein synthesis ✓
• D Activation of adenylate cyclase through calmodulin binding

Explanation

Fragment C of diphtheria toxin catalyses transfer of ADP-ribose from NAD onto elongation factor 2, irreversibly inactivating it and arresting translation, which kills the cell. Option B describes cholera toxin acting on Gs protein, option A describes tetanospasmin and botulinum toxin cleaving synaptobrevin and SNAP-25, and option D describes Bordetella pertussis toxin. The tox gene of Corynebacterium diphtheriae is acquired by lysogenic conversion via beta-corynephage.

Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.