Abstract
Bordetella pertussis causes the severe childhood disease whooping cough, by releasing several toxins, including pertussis toxin (PT) as a major virulence factor. PT is an AB5-type toxin, and consists of the enzymatic A-subunit PTS1 and five B-subunits, which facilitate binding to cells and transport of PTS1 into the cytosol. PTS1 ADP-ribosylates α-subunits of inhibitory G-proteins (Gαi) in the cytosol, which leads to disturbed cAMP signaling. Since PT is crucial for causing severe courses of disease, our aim is to identify new inhibitors against PT, to provide starting points for novel therapeutic approaches. Here, we investigated the effect of human antimicrobial peptides of the defensin family on PT. We demonstrated that PTS1 enzyme activity in vitro was inhibited by α-defensin-1 and -5, but not β-defensin-1. The amount of ADP-ribosylated Gαi was significantly reduced in PT-treated cells, in the presence of α-defensin-1 and -5. Moreover, both α-defensins decreased PT-mediated effects on cAMP signaling in the living cell-based interference in the Gαi-mediated signal transduction (iGIST) assay. Taken together, we identified the human peptides α-defensin-1 and -5 as inhibitors of PT activity, suggesting that these human peptides bear potential for developing novel therapeutic strategies against whooping cough.
Highlights
It was demonstrated that pertussis toxin (PT) causes severe and long-lasting inflammation of the airways in a mouse model [27]
B. pertussis strains not expressing PT did not cause leukocytosis, which is a hallmark of severe pertussis, or death. These results clearly indicate a pivotal role of PT in causing severe courses of disease, which makes it an attractive target for the development of novel pharmacological strategies [28,29,30]
Prompted by previous findings that defensins inhibited the enzyme activity of ADPribosylating toxins such as diphtheria toxin [31], we investigated whether defensins interfere with the enzyme activity of PTS1
Summary
The B-pentamer facilitates binding to the cell surface via sialoglycoproteins that are present on most cell types [1,4,5,6]. PT follows a retrograde intracellular transport through the Golgi to the endoplasmic reticulum (ER) [7]. This retrograde transport is inhibited by brefeldin A (BFA), which disrupts vesicle transport between the ER and Golgi apparatus [7,8]. In the ER, the binding of ATP to the toxin causes destabilization of the interaction between PTS1 and the B-pentamer, which results in the release of PTS1 from the holotoxin [9,10,11].
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