Arginase is a bimetallic enzyme that utilizes mainly Mn2+ or Co2+ for catalytic function. In human homolog, the substitution of Mn2+ with Co2+ significantly reduces the Km value without affecting the kcat. However, in the Helicobacter pylori counterpart (important for pathogenesis), the kcat increases nearly 4-fold with Co2+ ions both in the recombinant holoenzyme and arginase isolated from H. pylori grown with Co2+ or Mn2+. This suggests that the active site of arginase in the two homologs is modulated differently by these two metal ions. To investigate the underlying mechanism for metal-induced difference in catalytic activity in the H. pylori enzyme, we used biochemical, biophysical and microsecond molecular dynamics simulations studies. The study shows that the difference in binding affinity of Co2+ and Mn2+ ions with the protein is linked to a different positioning of a loop (–122HTAYDSDSKHIHG134–) that contains a conserved catalytic His133. Consequently, the proximity of His133 and conserved Glu281 is varied. We found that the Glu281–His133 interaction is crucial for catalytic function and was previously unexplored in other homologs. We suggest that the proximity difference between these two residues in the Co2+- and Mn2+-proteins alters the proportion of protonated His133 via variation in its pKa. This affects the efficiency of proton transfer — an essential step of l-arginine hydrolysis reaction catalyzed by arginase and thus activity. Unlike in human arginase, the flexibility of the above segment observed in H. pylori homolog suggests that this region in the H. pylori enzyme may be explored to design its specific inhibitors.
-
Cover Image
Cover Image
In this issue Qu and colleagues (pp. 3649–3660) have determined the crystal structure of TauA and have characterized its thermodynamic binding parameters by isothermal titration calorimetry in complex with taurine and different alkanesulfonates. The cover figure shows desolvation of the taurine binding protein TauA dictates ligand selectivity. TauA is shown in cartoon with taurine in red sticks. Water droplets indicate fully hydrated binding site. Image provided by Konstantinos Beis.
Metal-induced change in catalytic loop positioning in Helicobacter pylori arginase alters catalytic function
Ankita Dutta, Mohit Mazumder, Mashkoor Alam, Samudrala Gourinath, Apurba Kumar Sau; Metal-induced change in catalytic loop positioning in Helicobacter pylori arginase alters catalytic function. Biochem J 12 December 2019; 476 (23): 3595–3614. doi: https://doi.org/10.1042/BCJ20190545
Download citation file:
Sign in
Sign in to your personal account
Captcha Validation Error. Please try again.