2019 · Herdendorf — Staphylococcus aureus Evasion Proteins EapH1 and EapH2: Residue-Level Investigation of an Alternative Binding Motif for Human Neutrophil Elastase
Super-Abstract
Two bacterial immune-evasion proteins (EapH1 and EapH2) from Staphylococcus aureus inhibit a key human immune enzyme — neutrophil elastase — but use structurally different binding strategies. This in-vitro biochemistry study maps exactly which amino-acid residues in EapH2 are responsible for that inhibition. The findings illuminate how a pathogen evades neutrophil defences and could inform future anti-infective design. (Archives of Biochemistry and Biophysics, 2019.)
Commentary
This is a detailed structural biochemistry study with no direct connection to molecular hydrogen therapy. Herdendorf et al. investigate how two related bacterial proteins, EapH1 and EapH2, inhibit human neutrophil elastase (hNE) — a serine protease central to the innate immune response. The study finds that EapH2 binds hNE via a completely different binding motif than EapH1, with residue N127 as the main functional determinant. Molecular hydrogen does not feature as an intervention; the study appears in this database only because its journal-level indexing overlaps with biochemistry searches. The work is solid mechanistic biochemistry, but contributes nothing directly to the H₂ research field.
Key quotes
- „EapH2 has an altogether distinct hNE binding motif than EapH1“ — central structural finding: the two homologs use different inhibition mechanisms
- „inhibition of hNE by EapH2 is characterized by a rapid association rate (2.9 × 105 M-1s-1) coupled with a very slow dissociation rate (5.9 × 10-4 s-1), yielding an apparent inhibition constant of 2.11 nM“ — kinetic parameters showing extremely tight, slow-release binding
- „N127 is the main functional determinant in EapH2, and T125 serves an ancillary role aiding in the optimal orientation of N127“ — key residues identified by mutational analysis
Our assessment
This is a well-executed in-vitro biochemistry paper investigating bacterial immune evasion — it is not a hydrogen therapy study. No H₂ was administered; the „hydrogen“ referenced in the abstract refers to hydrogen bonds within protein crystal structures, which is standard chemistry. The paper has no direct relevance to molecular hydrogen (H₂) as a medical or nutritional intervention. It should be read as background structural biology rather than evidence for any H₂ health effect.
Study design
- Type: in-vitro biochemistry / kinetic and mutational analysis · Model: recombinant proteins (EapH1, EapH2, hNE); single amino-acid mutants · H₂ intervention: none
- Result: EapH2 inhibits hNE with Ki ≈ 2.11 nM via a distinct binding motif from EapH1; N127A mutation reduces inhibition ~200-fold; T125A abolishes time-dependence despite modest Ki effect
Abstract
The Staphylococcus aureusExtracellular Adherence Protein (Eap) and its homologs, EapH1 and EapH2, are a family of secreted proteins that potently inhibit the neutrophil serine proteases Neutrophil Elastase (hNE), Cathepsin G, and Proteinase 3. Similarly to EapH1, inhibition of hNE by EapH2 is characterized by a rapid association rate (2.9 × 105 M-1s-1) coupled with a very slow dissociation rate (5.9 × 10-4 s-1), yielding an apparent inhibition constant of 2.11 nM. As with EapH1, inhibition of hNE by EapH2 is also time-dependent in character. A phenylalanine in EapH2 replaces the leucine in EapH1 that sits over the hNE catalytic serine and creates a potential steric clash. Indeed, the EapH1 L59F mutant is severely decreased in its ability to inhibit hNE (~9500-fold). When compared to the EapH1:hNE co-crystal structure, a model of the EapH2:hNE complex predicts an alternative binding motif comprised of EapH2 residues 120-127. These putative interfacing residues were individually mutated and kinetically interrogated. The EapH2 N127A mutant resulted in the largest decrease in hNE inhibition (~200-fold) and loss of the time-dependent characteristic. Surprisingly, the time-dependent characteristic was still abolished in the EapH2 T125A mutant, even though it was less perturbed in hNE inhibition (~25-fold). T125 forms an intra-molecular hydrogen bond to the carbonyl oxygen of N127 in the EapH2 crystal structure. Given these observations, we conclude (i) that EapH2 has an altogether distinct hNE binding motif than EapH1, (ii) that N127 is the main functional determinant in EapH2, and (iii) that T125 serves an ancillary role aiding in the optimal orientation of N127.
Source & links
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