EXTRACELLULAR ASSOCIATION AND CYTOPLASMIC PARTITIONING OF THE IPAB AND IPAC INVASINS OF SHIGELLA-FLEXNERI

Shigella species cause bacillary dysentery in humans by invading colon ic epithelial cells. IpaB and IpaC, two major invasins of these pathog ens, are secreted into the extracellular milieu. We show here that Ipa B and IpaC form a complex in the extracellular medium and that each bi nds independently to a 17 kDa polypeptide, IpgC, in the bacterial cyto plasm. The IpgC polypeptide was found to be necessary for bacterial en try into epithelial cells, to stabilize the otherwise unstable IpaB pr otein, and to prevent the proteolytic degradation of IpaC that occurs through its association with unprotected IpaB. We propose that IpgC, w hich is not secreted and thus acts as a molecular chaperone, serves as a receptor that prevents premature oligomerization of IpaB and IpaC w ithin the cytoplasm of Shigella cells.