| Abstract
| - The Helicobacter pylori VacA causes large intracellular vacuoles in epithelial cells such asHeLa or RK13 cells. Two major VacA forms, m1 and m2, divergent in an ∼300 amino acid segmentwithin the cell binding domain P58, display distinct cell-type specificity. Sequence analysis of four vacAalleles showed that a m1-like allele (61) and two m2 alleles (62 and v226) mainly differed in the midregionand that v225, a m1m2 chimera, was a natural double crossover from v226 and another allele. Each ofthese alleles was expressed as a soluble GST−VacA fusion that did not form a large oligomer. Therecombinant VacA portion nevertheless assembled into higher ordered structures and possessed biologicalbinding activity similar to that of the native VacA. A direct comparison of fusion-cell binding activityshowed that m1 > m1m2 > m2 in HeLa cells, whereas there were more similar activities in RK13 cells.Vacuolating analyses of three forms revealed a positive correlation between cell binding activity andvacuolating activity. Moreover, the m1-type N-terminal half portion of the midregion was crucial forHeLa cell cytotoxicity. Kinetic, Scatchard, and inhibition analyses suggested the presence of at least tworeceptors: a m1-type specific high-affinity receptor (Kd = ∼5 nM) and a common VacA receptor interactingsimilarly with m1, m1m2, and m2 via a lower affinity (Kd = 45−67 nM). Expression of mainly them1-type receptor on HeLa cells whereas both receptors on RK13 cells may account for distinct cell bindingactivity and therefore for cell-type specificity.
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