DIFFUSE ADHERENCE OF ENTEROPATHOGENIC ESCHERICHIA-COLI STRAINS - PROCESSING OF AIDA-I

The adherence of pathogenic Escherichia coli to the mucosa of the smal l intestine is an important step in the development of diarrhoea. To s tudy the molecular basis of the diffuse adherence (DA) pattern of E. c oli strains expressing the classical serotypes of enteropathogenic E. coli (EPEC), strain 2787 (0126:H27) was investigated. By expression cl oning, a plasmid-derived 6.0 kb DNA fragment was identified which conf erred the DA phenotype on recipient K-12 strains. This fragment encode d the 100 kDa adhesin involved in diffuse adherence (AIDA-I) which by mild heat shock treatment was isolated from the surface of the wild-ty pe and recombinant DA-positive strains. Analysis of the entire DNA fra gment revealed two open reading frames coding for proteins of 45 kDa a nd 132 kDa, respectively. The 132 kDa protein has been identified as t he AIDA-I precursor protein which after cleavage of the signal sequenc e undergoes additional C-terminal processing for maturation to AIDA-I. Though the function of the cytoplasmic 45 kDa protein is not known, p reliminary evidence indicates that authentic expression of the protein is a prerequisite for the correct processing of the 132 kDa precursor to AIDA-I. The AIDA-I precursor exhibits significant homology to the virG (icsA) protein of Shigella flexneri which apparently plays a majo r role in the events leading to the intercellular spread of invasive S higella organisms.