Daf As A Receptor For Bacteria And Viruses

DAF has been shown to be a receptor for E. coli expressing Dr adhesins (Bernet-Camard et al., 1996; Nowicki et al., 1993; Pham et al., 1995; Pham et al., 1997). E. coli expressing fimbrial Dr, and afimbrial AFA-I, afimbrial AFA-III and fimbrial F1845 require CCP3 for attachment. Two dra-positive X strains (E. coli 8826 and E. coli 7372) bind CCP4 (Nowicki et al., 1990; Pham et al., 1995). DAF amino acid substitutions, S155A, C156A, and S165L (Hasan et al., 2002), completely block the binding of the Dr adhesin. Beyond DAF's CCPs, its GPI anchor appears to be involved in the Dr(+) E. coli internalization process (Selvarangan et al., 2000). Diseases of these bacteria include (gestational) pyelonephritis, cystitis, and diarrhea [reviewed in (Nowicki et al., 2001)]. One theory regarding the pathogenicity of E. coli bearing AFA/Dr adhesins in the intestine is that the adhesin-DAF interaction induces PMN transepithelial migration, and in turn the production of TNF-a and which upregulates intestinal DAF thereby creating more receptors for the bacterial binding (Betis et al., 2003).

Accumulating evidence indicates that certain viruses in Picornaviridae bind DAF. DAF is a receptor for echovirus 7 (Ward et al., 1994), coxsackieviruses B1, B3, and B5, and enterovirus 70 (Karnauchow et al., 1996; Shafren et al., 1995). The list now includes coxsackievirus A21; echoviruses 6, 11, 12 and 30; enterovirus 68 and human rhinovirus 87 (Blomqvist et al., 2002; Shafren et al., 1997a). While members of the coxsackievirus B-like B-cluster of human enteroviruses (coxsackievirus B 1, 3, and 5; echovirus 6, 7, 11, 12, and 30) bind CCPs 2-4 of DAF, members of the poliovirus-like C-cluster of human enteroviruses (coxsackievirus A21) and members of the enterovirus 70-like D-cluster of human enteroviruses (enterovirus 70) bind CCP1 (Powell et al., 1999). However, within these clusters, the binding sites of the viruses on DAF may not be the same. Mapping echovirus 7, echovirus 11, and echovirus 12 binding data on the crystal structure of CCPs 3-4 shows that echovirus 12 binding is negatively affected by E134A while echovirus 7 binding is positively affected by F169A, an amino acid on the opposite side of DAF CCP3 (Williams et al., 2003). Often, DAF is not the sole receptor for these viruses. Coxsackievirus A21 may bind ICAM-1 as well as DAF (Shafren et al., 1997a) and coxsackievirus B3 binds the coxsackie-adenovirus receptor (CAR) (Shafren et al., 1997b). Enterovirus 70 is believed to have an additional cell surface receptor (Alexander and Dimock, 2002). Although early work indicated that ICAM-1 was required for coxsackievirus A21 to enter cells (Shafren et al., 1997a), clinical isolates have been found which appear to infect DAF expressing cells without the aid of ICAM-1 or DAF-antibody cross-linking (Newcombe et al., 2004).

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