Insights into PG-binding, conformational change, and dimerization of the OmpA C-terminal domains from Salmonella enterica serovar Typhimurium and Borrelia burgdorferi.
Salmonella enterica serovar Typhimurium can induce both humoral and cell-mediated responses when establishing itself in the host. These responses are primarily stimulated against the lipopolysaccharide and major outer membrane (OM) proteins. OmpA is ...
Salmonella enterica serovar Typhimurium can induce both humoral and cell-mediated responses when establishing itself in the host. These responses are primarily stimulated against the lipopolysaccharide and major outer membrane (OM) proteins. OmpA is one of these major OM proteins. It comprises a N-terminal eight-stranded β-barrel transmembrane domain and a C-terminal domain (OmpA CTD ). The OmpA CTD and its homologs are believed to bind to peptidoglycan (PG) within the periplasm, maintaining bacterial osmotic homeostasis and modulating the permeability and integrity of the OM. Here we present the first crystal structures of the OmpA CTD from two pathogens: S. typhimurium (STOmpA CTD ) in open and closed forms and causative agent of Lyme Disease Borrelia burgdorferi (BbOmpA CTD ), in closed form. In the open form of STOmpA CTD , an aspartate residue from a long β2-α3 loop points into the binding pocket, suggesting that an anion group such as a carboxylate group from PG is favored at the binding site. In the closed form of STOmpA CTD and in the structure of BbOmpA CTD , a sulfate group from the crystallization buffer is tightly bound at the binding site. The differences between the closed and open forms of STOmpA CTD , suggest a large conformational change that includes an extension of α3 helix by ordering a part of β2-α3 loop. We propose that the sulfate anion observed in these structures mimics the carboxylate group of PG when bound to STOmpA CTD suggesting PG-anchoring mechanism. In addition, the binding of PG or a ligand mimic may enhance dimerization of STOmpA CTD , or possibly that of full length STOmpA.
Organizational Affiliation:
Center for Structural Genomics of Infectious Diseases, University of Chicago, 5735 South Ellis Avenue, Chicago, Illinois, 60637.,Structural Biology Center, Biosciences, Argonne National Laboratory, Argonne, Illinois, 60439.,National Security Directorate, Pacific Northwest National Laboratory, Richland, Washington, 99352.,Earth and Biological Sciences Directorate, Pacific Northwest National Laboratory, Richland, Washington, 99352.,Midwest Center for Structural Genomics, Argonne National Laboratory, Argonne, Illinois, 60439.
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