Outer Membrane–Peptidoglycan Anchoring in <i>Pseudomonas aeruginosa</i>

with the use of purified recombinant PA2854, OprI, and synthetic samples of the cell-wall peptidoglycan, in each case documenting the attachment of the side-chain ε-amino group of Lys83 of OprI to the peptide stem of the peptidoglycan. OprI forms a trimeric structure. The X-ray structure of the trimeric state of OprI was solved to 2.1 Å resolution, which reveals it as an extended 82 Å helix bundle. The X-ray structure of PA2854 was also solved at 2.63 Å resolution. The enzyme is composed of three domains, which were documented to bind to the synthetic peptidoglycan and to OprI. The enzyme turns over both non-cross-linked and cross-linked peptidoglycan as its substrate. A model for the ternary assembly of the complex of PA2854-OprI-peptidoglycan is proposed based on the collective evidence. We document that anchoring of the outer membrane to the cell wall catalyzed by PA2854 does not appear to be a redundant reaction (product of more than one enzyme), in the absence of which the bacterium shows a weakened envelope, prone to disruption.