Pasteurella multocida type D and rarely type A produce an about 145 kDa protein toxin called PMT (Pasteurella multocida Toxin). The toxin is the major cause of bone-destruction in progressive atrophic rhinitis induced by the pathogen. During recent years our knowledge about the molecular biology of the toxin has largely increased. The toxin consists of an N-terminal part, which is involved in receptor binding and cellular up-take. The C-terminal part consists of 3 domains (C1, C2 and C3) and harbors the biological activity of the toxin. It was shown that domain C3 of PMT acts as a deamidase, which targets heterotrimeric G proteins of the Gi,o Gq/11 and G12/13 family. Heterotrimeric G proteins are activated by GDP/GTP exchange induced by heptahelical membrane receptors (G-protein-coupled receptors, GPCRs) and their active state is terminated by hydrolysis of GTP. PMT causes deamidation of a specific glutamine residue of the α-subunits of the G proteins thereby inhibiting GTP hydrolysis, which causes constitutive activation of the G protein and strong activation of downstream signal pathways. How PMT-induced activation of G proteins causes destruction of bones (e.g., nasal turbinates in atrophic rhinitis) is topic of recent research and will be discussed.