RTX cytotoxins recognize β 2 integrin receptors through N-linked oligosaccharides

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Abstract
Bordetella pertussis adenylate cyclase (AC) toxin–hemolysin (Hly) (CyaA, ACT, or AC-Hly) is a cytotoxin of the RTX (repeat in toxin) family. It delivers into target cells an AC domain that catalyzes uncontrolled conversion of ATP to cAMP, a key signaling molecule subverting phagocyte functions. CyaA utilizes a heavily N-glycosylated β 2 integrin receptor CD11b/CD18 (α M β 2 , Mac-1, or CR3). We show that deglycosylation of cell surface proteins by glycosidase treatment, or inhibition of protein N-glycosylation by tunicamycin, ablates CyaA binding and penetration of CD11b-expressing cells. Furthermore, binding of CyaA to cells was strongly inhibited in the presence of free saccharides occurring as building units of integrin oligosaccharide complex, whereas saccharides absent from integrin oligosaccharide chains failed to inhibit CyaA binding to CD11b/CD18-expressing cells. CyaA, hence, selectively recognized sugar residues of N-linked oligosaccharides of integrins. Moreover, glycosylation of CD11a/CD18, another receptor of the β 2 integrin family, was also essential for cytotoxic action of other RTX cytotoxins, the leukotoxin of Aggregatibacter actinomycetemcomitans (LtxA) and the Escherichia coli α-Hly (HlyA). These results show that binding and killing of target cells by CyaA, LtxA, and HlyA depends on recognition of N-linked oligosaccharide chains of β 2 integrin receptors. This sets a new paradigm for action of RTX cytotoxins.