Structure of the OmpA‐like domain of RmpM from Neisseria meningitidis

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Abstract
Summary: RmpM is a putative peptidoglycan binding protein from Neisseria meningitidis that has been shown to interact with integral outer membrane proteins such as porins and TonB‐dependent transporters. Here we report the 1.9 Å crystal structure of the C‐terminal domain of RmpM. The 150‐residue domain adopts a βαβαββ fold, as first identified in Bacillus subtilis chorismate mutase. The C‐terminal RmpM domain is homologous to the periplasmic, C‐terminal domain of Escherichia coli OmpA; these domains are thought to be responsible for non‐covalent interactions with peptidoglycan. From the structure of the OmpA‐like domain of RmpM, we suggest a putative peptidoglycan binding site and identify residues that may be essential for binding. Both the crystal structure and solution experiments indicate that RmpM may exist as a dimer. This would promote more efficient peptidoglycan binding, by allowing RmpM to interact simultaneously with two glycan chains through its C‐terminal, OmpA‐like binding domain, while its (structurally uncharacterized) N‐terminal domain could stabilize oligomers of porins and TonB‐dependent transporters in the outer membrane.