An evolutionary non-conserved motif in Helicobacter pylori arginase mediates positioning of the loop containing the catalytic residue for catalysis

Illuminating the structure-function landscape of an evolutionary nonconserved motif in the arginases of Helicobacter gastric pathogens

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 (-153 ESEEKAWQKLCSL165 -) 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.

Differential role of Pax6 and its interaction with Shh-Gli1-IDH2 axis in regulation of glioma growth and chemoresistance

Glioma is a major brain tumor, and the associated mortality rate is very high. Contemporary therapies provide a chance of survival for 9-12 months. Therefore, a novel approach is essential to improve the survival rate. Sonic hedgehog (Shh) cell signaling is critical for early development in various tumors. This investigation attempted to explore the potential interaction and regulation of Shh-Gli1 cell signaling in association with paired box 6 (Pax6) and isocitrate dehydrogenase 2 (IDH2). The expression pattern of Shh, Gli1, Pax6, and IDH2 was examined by transcriptome analysis, immunohistochemistry, and confocal images. The results suggest the interaction of Shh-Gli1 cell signaling pathway with Pax6 and IDH2 and potential regulation. Thereafter, we performed protein-protein docking and molecular dynamic simulations (MDS) of Gli1 with Pax6 and IDH2. The results suggest differential dynamic interactions of Gli1-IDH2 and Gli1-Pax6. Gli1 knockdown downregulated the expression of Pax6 and upregulated the expression of IDH2. Moreover, Gli1 knockdown decreased the expression of the drug resistance gene MRP1. The knockdown of Pax6 gene in glioma cells downregulated the expression of Gli1 and IDH2 and promoted cell proliferation. Moreover, the efficacy of the treatment of glioma cells with temozolomide (TMZ) and Gli1 inhibitor GANT61 was higher than that of TMZ alone. MDS results revealed that the interactions of Gli1 with IDH2 were stronger and more stable than those with Pax6. Intriguingly, inhibition of Pax6 promoted glioma growth even in the presence of TMZ. However, the tumor-suppressive nature of Pax6 was altered when Gli1 was inhibited by GANT61, and it showed potential oncogenic character, as observed in other cancers. Therefore, we conclude that Pax6 interacted with IDH2 and Gli1 in glioma. Moreover, the Shh-Gli1-IDH2/Pax6 cell signaling axis provides a new therapeutic approach for inhibiting the progression of the disease and mitigating drug resistance in glioma.

A unique aromatic cluster near the active site of H. pylori CPA is essential for catalytic function

Polyamines are essential for cell growth and proliferation. In plants and many bacteria, including Helicobacter pylori, the parent polyamine putrescine is only produced through the metabolism of N-carbamoylputrescine by N-carbamoylputrescine amidase (CPA). Thus, CPA is a crucial intermediate enzyme. Moreover, the absence of CPA in humans makes its presence in H. pylori a potential target for the development of new therapeutics against this pathogen. Despite this enzyme's presence in plants and bacteria, its function is not completely explored. Using structure-guided biochemical and biophysical studies on H. pylori CPA, we discovered an aromatic cluster containing four conserved tryptophans near the catalytic site and elucidated its role. Mutational studies revealed that they are individually vital to enzyme function. Unlike wild-type, which forms a hexamer, the Trp to Ala mutants only formed dimers. Interestingly, two other conserved residues, Gln155 and Asp278, interact with the tryptophan cluster and perform similar roles. Our results indicate that aromatic-aromatic and H-bonding contacts between the residues (Trp156-Trp273, Trp196-Gln155, and Trp153-Asp278) play a crucial role in stimulating activity through hexamer formation. Additionally, Trp156 is essential to generating a catalytically efficient hexamer. These results suggest dual roles for the tryptophans; in hexamer formation and in generating its functionally active form, thereby providing a mechanistic understanding into the role of the cluster. We also elucidated the catalytic roles of Glu43, Lys115, and Cys152, which are present at the active site. Our findings highlight, for the first time, the importance of a tryptophan cluster in H. pylori CPA that can be exploited to design therapeutic inhibitors.