ProRgpB inhibitor loop variants V126K, E131D, N132R significantly boost RgpB affinity *in silico*
Background
Porphyromonas gingivalis (P. gingivalis) is a keystone pathogen in periodontal disease and is increasingly linked to systemic conditions like Alzheimer's disease and inflammatory arthritis. Its primary virulence factor, Arginine-specific gingipain B (RgpB), is a cysteine protease that degrades host proteins and evades immune responses. RgpB is initially synthesized with a propeptide inhibitor that prevents premature activation. However, this natural inhibition is overcome in the extracellular environment, allowing RgpB to exert its pathogenic effects. Developing potent inhibitors against RgpB is crucial for therapeutic strategies, but current approaches often lack specificity or sufficient affinity. This study addresses the need for optimized RgpB inhibitors by leveraging the natural propeptide structure.
Study Design
Researchers designed 52 mutant variants of the ProRgpB inhibitory loop to enhance its binding affinity for RgpB. For each variant model, four independent molecular dynamics replicas were performed to simulate molecular interactions. Subsequently, binding free energy calculations were conducted using MM/GBSA (Molecular Mechanics/Generalized Born Surface Area) to quantify the interaction strength. Promising variants were further validated with Thermodynamic Integration calculations. The wild-type (WT) loop served as the control for comparison, with its binding affinity measured at -109.8 ± 4.9 kcal mol-1.
Results
Most of the 52 designed variants of the ProRgpB inhibitory loop exhibited more favorable binding affinities for RgpB compared to the wild-type (WT) loop.
> The most promising variants identified were V126K with an affinity of -128.1 ± 5.6 kcal mol-1, E131D at -120.6 ± 8.2 kcal mol-1, and N132R showing the strongest affinity at -135.8 ± 4.6 kcal mol-1.
Statistical analysis using ANOVA followed by Tukey's post-hoc test confirmed that V126K and E131D showed statistically significant improvements in binding affinity (p = 0.001) compared to the WT. Thermodynamic Integration calculations consistently corroborated these findings, confirming a significant increase in relative binding affinity for the selected variants. These in silico results strongly suggest that specific amino acid substitutions within the ProRgpB inhibitory loop can dramatically improve its inhibitory potential against RgpB by enhancing binding affinity, providing a solid basis for future experimental validation.
Key Findings
- Most of 52 designed ProRgpB inhibitor loop variants showed more favorable binding affinities than the WT loop (-109.8 ± 4.9 kcal mol-1).
- Variant V126K exhibited significantly enhanced affinity at -128.1 ± 5.6 kcal mol-1 (p = 0.001).
- Variant E131D also showed significant improvement with an affinity of -120.6 ± 8.2 kcal mol-1 (p = 0.001).
- Variant N132R demonstrated the strongest affinity at -135.8 ± 4.6 kcal mol-1.
- Thermodynamic Integration calculations confirmed increased binding affinity for selected variants.
Why It Matters
This study provides a robust in silico framework for the rational design of highly potent RgpB inhibitors, a critical step towards new therapies for periodontal disease and associated systemic conditions. Optimized ProRgpB inhibitor loop variants offer a promising blueprint for developing novel peptide-based drugs that specifically target P. gingivalis virulence. The identified mutations (e.g., V126K, N132R) could inform the synthesis of next-generation peptide therapeutics, potentially leading to more effective and targeted treatments than current broad-spectrum approaches. While in vitro and in vivo validation are still needed, this computational approach significantly accelerates the initial discovery phase, offering a pathway to translate these findings into clinically relevant protocols for managing P. gingivalis infections and mitigating its systemic impact.
porphyromonas-gingivalis
rgpb
gingipain
protease-inhibitor
peptide-design
in-silico