Unique dimeric structure of the DUF2891 family protein CJ0554 from Campylobacter jejuni

Campylobacter jejuni is a pathogenic bacterium that causes enteritis and Guillain-Barre syndrome in humans. To identify a protein target for the development of a new therapeutic against C. jejuni infection, each gene product of C. jejuni must be functionally characterized. The cj0554 gene of C. jejuni encodes a DUF2891 family protein with unknown functions. To provide functional insights into CJ0554, we determined and analyzed the crystal structure of the CJ0554 protein. CJ0554 adopts an (α/α)6-barrel structure, which consists of an inner α6 ring and an outer α6 ring. CJ0554 assembles into a dimer in a unique top-to-top orientation that is not observed in its structural homologs, N-acetylglucosamine 2-epimerase superfamily members. Dimer formation was verified by analyzing CJ0554 and its ortholog protein through gel-filtration chromatography. The top of the CJ0554 monomer barrel harbors a cavity, which is connected to that of the second subunit in the dimer structure, generating a larger intersubunit cavity. This elongated cavity accommodates extra nonproteinaceous electron density, presumably as a pseudosubstrate, and is lined with generally catalytically active histidine residues that are invariant in CJ0554 orthologs. Therefore, we propose that the cavity functions as the active site of CJ0554. •CJ0554 from Campylobacter jejuni belongs to the DUF2891 family.•CJ0554 adopts an (α/α)6-barrel structure and houses a cavity on the top.•CJ0554 dimerizes in a unique top-to-top orientation.•Invariant histidine residues in the cavity likely form the active site of CJ0554.