The binuclear metalloenzyme Helicobacter pylori arginase is important for pathogenesis of the bacterium in the human stomach. Despite conservation of the catalytic residues, this single Trp enzyme has an insertion sequence (--153ESEEKAWQKLCSL165--) that is extremely crucial to function. This sequence contains the critical residues, which are conserved in the homologue of other Helicobacter gastric pathogens. However, the underlying basis for the role of this motif in catalytic function is not completely understood. Here, we used biochemical, biophysical and molecular dynamics simulations studies to determine that Glu155 of this stretch interacts with both Lys57 and Ser152. These interactions are essential for positioning of the motif through Trp159, which is located near Glu155 (His122-Trp159-Tyr125 contact is essential to tertiary structural integrity). The individual or double mutation of Lys57 and Ser152 to Ala considerably reduces catalytic activity with Lys57 to Ala being more significant, indicating they are crucial to function. Our data suggest that the Lys57-Glu155-Ser152 interaction influences the positioning of the loop containing the catalytic His133 so that this His can participate in catalysis, thereby providing a mechanistic understanding into the role of this motif in catalytic function. Lys57 was also found only in the arginases of other Helicobacter gastric pathogens. Based on the non-conserved motif, we found a new molecule, which specifically inhibits this enzyme. Thus, the present study not only provides a molecular basis into the role of this motif in function, but also offers an opportunity for the design of inhibitors with greater efficacy.

No abstract

The bimetallic enzyme arginase catalyses the conversion of L‐arginine to L‐ornithine and urea. In Helicobacter pylori (a known human gastric pathogen), this enzyme is an important virulence factor. In spite of the conservation of the catalytic and the metal‐binding residues, the H. pylori homolog possesses a 13‐residue motif (–153ESEEKAWQKLCSL165–) present in the middle of the protein sequence, whose role was recently elucidated. Despite several reviews available on arginases, no report has thoroughly illustrated the underlying basis for the importance of the above motif of the H. pylori enzyme in structure and function. In this review, we systematically describe a mechanistic basis for its importance in structure and function based on the known data. This motif of the H. pylori enzyme is present exclusively in the arginases of other Helicobacter gastric pathogens, where the critical residues are conserved, implying that the nonconserved stretch has been selected during the evolution of the enzyme in these gastric pathogens in a specific manner to perform its role in the structure and function. The combined information can be useful for understanding the function of arginases in other Helicobacter gastric pathogens. Additionally, this knowledge can be utilised to screen and design new small molecule inhibitors, specific to the arginases of these pathogens.