C-terminal amino acid residues of the trimeric autotransporter adhesin YadA of Yersinia enterocolitica are decisive for its recognition and assembly by BamA.

The Bam complex is a highly conserved multiprotein machine essential for the assembly of β-barrel outer membrane proteins. It is composed of the essential outer membrane protein BamA and four outer membrane associated lipoproteins BamB-E. The Yersinia enterocolitica Adhesin A (YadA) is the prototype of trimeric auotransporter adhesins (TAAs), consisting of a head, stalk and a β-barrel membrane anchor. To investigate the role of BamA in biogenesis of TAAs, we expressed YadA in a BamA-depleted strain of Escherichia coli, which resulted in degradation of YadA. Yeast-two-hybrid experiments and immunofluorescence studies revealed that BamA and YadA interact directly and colocalize. As BamA recognizes the C-terminus of OMPs, we exchanged the nine most C-terminal amino acids of YadA. Substitution of the amino acids in position 1, 3 or 5 from the C-terminus with glycine resulted in DegP-dependent degradation of YadA. Despite degradation all YadA proteins assembled in the outer membrane. In summary we demonstrate that (i) BamA is essential for biogenesis of the TAA YadA, (ii) BamA interacts directly with YadA, (iii) the C-terminal amino acid motif of YadA is important for the BamA-dependent assembly and differs slightly compared with other OMPs, and (iv) BamA and YadA colocalize.