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Mast cell degranulation is important in the pathogenesis of anaphylaxis and allergic disorders. Many animal venoms contain components that can induce mast cell degranulation, and this has been thought to contribute to the pathology and mortality caused by envenomation. However, we recently reported evidence that mast cells can enhance the resistance of mice to the venoms of certain snakes and that mouse mast cell-derived carboxypeptidase A3 (CPA3) can contribute to this effect. Here, we investigated whether mast cells can enhance resistance to the venom of the Gila monster, a toxic component of that venom (helodermin), and the structurally similar mammalian peptide, vasoactive intestinal polypeptide (VIP). Using 2 types of mast cell-deficient mice, as well as mice selectively lacking CPA3 activity or the chymase mouse mast cell protease-4 (MCPT4), we found that mast cells and MCPT4, which can degrade helodermin, can enhance host resistance to the toxicity of Gila monster venom. Mast cells and MCPT4 also can limit the toxicity associated with high concentrations of VIP and can reduce the morbidity and mortality induced by venoms from 2 species of scorpions. Our findings support the notion that mast cells can enhance innate defense by degradation of diverse animal toxins and that release of MCPT4, in addition to CPA3, can contribute to this mast cell function.

MARTX toxins modulate the virulence of a number of Gram-negative Vibrio species. This family of toxins is defined by the presence of a cysteine protease domain (CPD), which proteolytically activates the Vibrio cholerae MARTX toxin. Although recent structural studies of the CPD have uncovered a novel allosteric activation mechanism, the mechanism of CPD substrate recognition or toxin processing is unknown. Here, we show that interdomain cleavage of MARTXVc enhances effector domain function. We also identify the first small molecule inhibitors of this protease domain and present the 2.35 Å structure of the CPD bound to one of these inhibitors. This structure, coupled with biochemical and mutational studies of the toxin, reveals the molecular basis of CPD substrate specificity and underscores the evolutionary relationship between the CPD and the clan CD caspase proteases. These studies are likely to prove valuable for devising novel anti-toxin strategies for a number of bacterial pathogens.

An unusual type of glycosylation has been observed for tissue plasminogen activator (t-PA). The monosaccharide fucose is glycosidically linked to threonine-61 in the epidermal growth factor region of t-PA. The presence of O-linked fucose was demonstrated by carbohydrate analysis and mass spectrometry of tryptic and chymotryptic peptides that contain this site. The susceptibility of the fucose residue to alpha-fucosidase indicated that it was in the alpha-anomeric configuration. Fucosylation of threonine-61 was observed in t-PA isolated from the Bowes melanoma cell line and from recombinant expression systems using Chinese hamster ovary or human embryonic kidney cells. Fucosylation of the homologous residue in prourokinase has also been reported recently. Our results indicate that this novel type of glycosylation may be common to the epidermal growth factor domains found in coagulation and fibrinolytic proteins and, therefore, suggest that the modification may have functional significance.