Abstract
The Yersinia adhesin YadA is the prototype of a novel class of bacterial adhesins which form oligomeric lollipop-like structures and are anchored in the outer membrane by the C terminus. For YadA, six different regions (R) or domains (D) are predicted from the amino acid sequence: the N-terminal leader sequence, head-D, neck-D, stalk-D, linking-R, and a C-terminal transmembrane region consisting of four beta-strands. To identify structural and functional features of these domains, we performed in-frame deletion mutagenesis and constructed N-terminally tagged YadA variants. Diverse YadA variants were analyzed for outer membrane localization, surface exposure, oligomerization adhesion properties, and ability to protect against complement-mediated lysis. We demonstrated that (i) the C-terminal region (amino acids [aa] 353 to 422) is sufficient for outer membrane insertion and formation of trimers in the outer membrane; (ii) the head, neck, and stalk domains (aa 26 to 330) are surface exposed, forming a passenger domain; and (iii) the linking region (aa 331 to 369) is responsible for outer membrane translocation of the passenger domain. Thus, YadA meets all the criteria of an autotransporter. The same may be true for all other members of the YadA family, forming a subfamily of surface-attached oligomeric autotransporters. Moreover, in-frame truncation mutagenesis suggested that the head and neck domains together form the YadA-binding module which is located on the top of the stalk. However, the YadA-binding module did not confer serum resistance. Mutants lacking the head and neck domain were resistant to complement-mediated lysis. In-frame truncation of the stalk domain did not result in significant attenuation of the mutant in an orogastric mouse infection model.