Lpg0406, a hypothetical protein from Legionella pneumophila, belongs to carboxymuconolactone decarboxylase (CMD) family. We determined the crystal structure of lpg0406 both in its apo and reduced form. The structures reveal that lpg0406 forms a hexamer and have disulfide exchange properties. The protein has an all-helical fold with a conserved thioredoxin-like active site CXXC motif and a proton relay system similar to that of alkylhydroperoxidase from Mycobacterium tuberculosis (MtAhpD), suggesting that lpg0406 might function as an enzyme with peroxidase activity and involved in antioxidant defense. A comparison of the size and the surface topology of the putative substrate-binding region between lpg0406 and MtAhpD indicates that the two enzymes accommodate the different substrate preferences. The structural findings will enhance understanding of the CMD family protein structure and its various functions.

Aminopeptidases are a group of exopeptidases that catalyze the removal of a wide range of N-terminal amino acid residues from peptides and proteins. They have many important commercial applications in the food industry. We determined the crystal structure of an aminopeptidase LapB from Legionella pneumophila. The overall structure reveals that the N-terminal protease-associated (PA) domain presents a new fold and shields the active site cavity of the conserved C-terminal peptidase domain. The steady-state kinetic analysis of LapB and the PA domain deletion mutant indicate that the PA domain inhibited enzyme activity of the peptidase domain. Interestingly, the activity of LapB was largely increased by various organic solvents such as ethanol, propanol, and methanol at the concentration of 60% (v/v). CD analysis provided evidence that organic solvents induce the PA domain conformational changes that eliminate the inhibition role. The unique properties indicate the application potential of LapB in the food processing industry.

The Legionella pneumophila type II secretion system can promote bacterial growth under a wide variety of conditions and mediates the secretion of more than 25 proteins, including the uncharacterized effector Lpg2622. Here, we determined the crystal structures of apo-Lpg2622 and Lpg2622 in complex with the cysteine protease inhibitor E64. Structural analysis suggests that Lpg2622 belongs to the C1 family peptidases. Interestingly, unlike the other structurally resolved papain-like cysteine proteases, the propeptide of Lpg2622 forms a novel super-secondary structural fold (hairpin-turn-helix) and can be categorized into a new group. In addition, the N-terminal β-sheet of the Lpg2622 propeptide plays a regulatory role on enzymatic activity. This study enhances our understanding of the classification and regulatory mechanisms of the C1 family peptidases.

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Dephospho-CoA kinase (DPCK; EC 2.7.1.24) catalyzes the final step in the coenzyme A biosynthetic pathway. DPCK transfers a phosphate group from ATP to the 3-hydroxyl group of the ribose of dephosphocoenzyme A (dCoA) to yield CoA and ADP. Upon the binding of ligands, large conformational changes is induced in DPCKs, as well as in many other kinases, to shield the bound ATP in their catalytic site from the futile hydrolysis by bulk water molecules. To investigate the molecular mechanisms underlying the phosphoryl transfer during DPCK catalytic cycle, we determined the crystal structures of the Legionellapneumophila DPCK (LpDPCK) both in its apo-form and in complex with ATP. The structures reveal that LpDPCK comprises of three domains, the classical core domain, the CoA domain, and the LID domain, which are packed together to create a central cavity for substrate-binding and enzymatic catalysis. The binding of ATP induces large conformational changes, including a hinge-bending motion of the CoA binding domain and the "helix to loop" conformational change of the P-loop. Finally, modeling of a dCoA molecule to the enzyme provides insights into the catalytic mechanism of DPCK.