β-Propeller structure of the CJ1041C protein from Campylobacter jejuni and its interaction with Ca 2+ ions

Campylobacter jejuni, the primary bacterial cause of foodborne enteric disease globally, poses a significant health threat due to the rising presence of antibiotic-resistant strains. Identifying novel protein targets for antibacterial drug development becomes crucial through the functional analysis of lesser-studied C. jejuni proteins.

One such protein is CJ1041C, whose role remains unexplored experimentally. To investigate CJ1041C, researchers determined its crystal structures in both apo form and complex with Ca2+ ions. The protein exhibits a six-bladed β-propeller architecture, characterized by six four-stranded β-sheets arranged around a central channel. In the apo form, this channel is closed and contains two negatively charged cavities.

The upper cavity specifically coordinates a Ca2+ ion through conserved residues and also accommodates a glycerol molecule, which may act as a substrate–water mimic. The Ca2+-binding configuration of CJ1041C mirrors that observed in β-propeller lactonases, implying that the protein functions as a lactonase or lactonase-like enzyme.

However, the unique glycerol-binding mode of CJ1041C, along with phylogenetic and sequence analyses, suggests that it is a distinct member of the β-propeller lactonase family. This protein likely possesses catalytic activity towards noncanonical substrates. The authors acknowledge the support from the National Research Foundation of Korea and the ANCHOR program.