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B6db references: 29684243

type Journal Article
authors Alam M, Srivastava A, Dutta A, Sau AK
title Biochemical and biophysical studies of Helicobacter pylori arginine decarboxylase, an enzyme important for acid adaptation in host
journal IUBMB Life
sel selected
ui 29684243
year (2018)
volume 70
pages 658-669
keywords activity; circular dichroism; inhibition; thermal stability
abstract Despite importance of arginine decarboxylase (ADC: EC of Helicobacter pylori (H. pylori) 26695 pathogenic strain for acid adaptation in host, the enzyme has not yet been studied at a molecular level. Using combined approaches that include kinetic assays, site-directed mutagenesis, circular dichroism, heat-induced denaturation, analytical gel-filtration, and homology modeling, we report here a detailed investigation of H. pylori ADC. The pyridoxal 5'-phosphate (PLP)-dependent enzyme exhibits higher catalytic activity in the presence of Mg2+ ions at pH ∼8.5. Unlike other bacterial ADCs, this homolog exists as a hexamer. The higher thermal stability (Tm ∼65.8  0.2 C) of the enzyme observed from the heat-induced circular dichroism measurements indicates its secondary structural stabilization in the presence of PLP. The kinetic parameters Km and kcat of the enzyme are determined to be 3.4  0.2 mM and 55.2  1.0 min-1 , respectively. We elucidate that Cys487, a conserved residue located at the active-site, is involved in the catalysis, whose pKa value was estimated to be ∼7.2. The homology model of the protein show conserved α/β TIM barrel and β-sandwich domains, which are characteristic features of fold III decarboxylases. A lower sequence identity (∼21%) of this enzyme compared with its human counterpart has enabled us to screen putative inhibitors of H. pylori ADC. We found that α-difluoromethylarginine inhibits the activity of the H. pylori enzyme competitively with a Ki value ∼118 M and thus it can serve as a basis to design inhibitors with higher efficacy against this ADC.
last changed 2018/10/05 11:38

B6db references