A clinical isolate of the stomach bacterium Helicobacter pylori has handed researchers a clear example of how evolution can tune an enzyme without touching its catalytic heart. Scientists studying a strain known as G272 found that it tolerated hydrogen peroxide better than the widely used reference strain 26695, and they traced part of that biochemical edge to two amino acids, P160 and K287, which sit outside the catalytic center of the bacterial enzyme catalase. The work, published in BMC Microbiology, shows that naturally occurring sequence variation away from the active site can measurably change how fast this defensive enzyme works.
H. pylori lives in a hostile neighborhood. During colonization of the gastric lining, the bacterium is exposed to oxidative stress, including hydrogen peroxide generated by host defenses. Catalase, encoded by the katA gene, is one of the microbe’s major shields against this compound, breaking it down before it can inflict damage. Although KatA is highly conserved across H. pylori strains, the functional consequences of the small sequence differences that do occur between strains have remained poorly understood, which is what motivated the new analysis.
The team began with a straightforward comparison. Under the assay conditions used in the study, G272 withstood hydrogen peroxide exposure better than 26695. To confirm that catalase was responsible for the detectable peroxide-breaking activity in intact cells, the researchers disrupted the katA gene in G272. That single genetic change abolished detectable whole-cell catalase activity, and inserting a working copy back into the chromosome restored it. The result established KatA as the enzyme behind the phenotype the team wanted to explain.
Next came the biochemistry. The researchers expressed KatA proteins from both strains in Escherichia coli, purified them, and measured their specific catalytic activity under standard conditions. KatA from G272 reached 3,593 ± 207 units per milligram of protein, while KatA from 26695 reached 2,918 ± 130 units per milligram. That gap pointed to real enzymatic differences encoded in the two protein sequences rather than differences in gene expression or cellular environment alone.
Comparing the two sequences revealed only five amino acid differences between the enzymes. To decide which of these might matter, the authors turned to a published dataset of H. pylori KatA sequences and found that the variants carried by G272 at positions 160 and 287 were common in nature, not one-off quirks of a single isolate. Structure-guided mapping then flagged P160 and K287 as the most promising candidates for functional testing, since neither residue belongs to the catalytic machinery itself.
To test the idea directly, the team used site-directed mutagenesis to build two G272-derived enzymes: KatAG272-P160H, in which proline 160 is swapped for the histidine found in the reference strain, and KatAG272-K287Q, in which lysine 287 is replaced by glutamine. If these two positions were merely passive passengers, the swaps should leave activity untouched. Instead, both substitutions reduced the catalytic activity of the G272 enzyme under multiple pH and temperature conditions, and the effect persisted at selected pre-incubation time points designed to probe how activity is retained over time.
The experiments went beyond a single activity number. The four recombinant proteins, the two natural variants and the two engineered mutants, were compared for their pH and temperature responses and for time-dependent activity retention after pre-incubation. The consistent pattern across these different measurements strengthens the conclusion that P160 and K287 are genuine contributors to the enhanced performance of the G272 enzyme, rather than artifacts of one particular assay condition.
The authors are careful about what this does and does not prove. Their conclusion is that the noncatalytic residues P160 and K287 contributed to the higher catalytic activity of KatAG272, supporting the functional relevance of naturally occurring sequence variation outside the catalytic center. They also note that these enzyme-level differences may contribute to strain-level variation in peroxide tolerance, but that direct chromosomal replacement experiments, swapping the residues in the bacterial genome itself, would be needed to determine whether P160 and K287 influence the whole-cell tolerance phenotype in H. pylori. The enzyme data and the cell-level phenotype are connected observations, not yet a demonstrated causal chain.
Even with that caveat, the study adds a useful piece to a larger puzzle. H. pylori infects a large share of the world’s population and its ability to survive oxidative attack in the stomach is central to its persistence. Understanding how peroxide tolerance varies between strains, and which sequence differences underlie that variation, could inform how researchers think about strain diversity in this pathogen. The finding that two common, naturally occurring variants outside the active site can shift catalytic output also serves as a reminder that enzyme evolution often works through subtle adjustments far from the residues that carry the reaction itself.
Subject of Research: How two noncatalytic amino acid variants enhance catalase activity in a clinical Helicobacter pylori strain
Article Title: Noncatalytic residues P160 and K287 contribute to the enhanced catalytic activity of catalase from a clinical Helicobacter pylori strain
Article References: Wang, X., Li, X., Guan, Y., Wu, D., Hong, W., Yang, Y., Chen, Z., Feng, Y., & Cui, G. (2026). Noncatalytic residues P160 and K287 contribute to the enhanced catalytic activity of catalase from a clinical Helicobacter pylori strain. BMC Microbiology. https://doi.org/10.1186/s12866-026-05868-x
Image Credits: AI Generated
DOI: 10.1186/s12866-026-05868-x
Keywords: Helicobacter pylori, catalase, KatA, hydrogen peroxide, oxidative stress, site-directed mutagenesis, enzyme kinetics, noncatalytic residues, strain variation, gastric colonization, protein sequence variation, BMC Microbiology
