B-286. The Escherichia coli AIDA-I Autotransporter Undergoes Glycosylation Independently of Export

M-E. Charbonneau, M. Mourez;
Univ. de Montréal, Saint-Hyacinthe, QC, CANADA.

The Escherichia coli Adhesin Involved in Diffuse Adherence (AIDA-I) is one of the few glycosylated proteins found in Escherichia coli. O-glycosylation is mediated by the aah gene which codes for a specific heptosyltransferase that is located at the cytoplasmic face of the inner membrane. Little is still know about the mechanism involved in this modification. In eukaryotes and some Gram positive bacteria, O-glycosylation can be coupled with secretion. We therefore asked if the same coupling occurred for the AIDA-I autotransporter. By deleting the whole signal sequence or by blocking the sec-translocation machinery with sodium azide, we showed that glycosylation can occur in the cytoplasm of the bacteria without any requirement for secretion. AIDA-I harbors an extended signal sequence of 49 amino acids, specific role of which remains controversial. We observed that deletion of the N-terminal signal sequence extension affected the expression level of the protein but that the protein is still exported to the outer membrane and glycosylated. This confirms the lack of correlation between secretion and glycosylation. Cytoplasmic glycosylation is, to our knowledge, an extremely rare event in the biogenesis of glycoproteins of Gram negative bacteria.