Computational Physicochemical Characterization, Comparative Structural Modeling, and Active-Site Mapping of Catalase-Peroxidase from Talaromyces marneffei

Abstract

Introduction: Talaromyces marneffei is a pathogenic dimorphic fungus causing severe systemic mycosis in immunocompromised hosts. To survive within host macrophages, it relies heavily on catalase-peroxidase (KatG) to neutralize hostile reactive oxygen species (ROS). However, its specific physicochemical and structural properties remain poorly understood.

Objectives: This study aims to evaluate the primary physicochemical profiles and predict the three-dimensional (3D) macromolecular configuration of T. marneffei catalase-peroxidase using computational workflows.

Material and Methods:. The primary sequence of T. marneffei KatG (UniProt ID: Q8NJN2) was characterized using ExPASy ProtParam, hydropathy plots, and SignalP. A 3D dual-modeling pipeline was executed via AlphaFold and SWISS-MODEL, validated using Ramachandran plots, ERRAT, and Verify3D, and mapped using PyMOL rendering.

Results: Physicochemical profiling revealed a stable (Instability Index: 25.15), thermally resilient (Aliphatic Index: 72.35), and hydrophilic protein (GRAVY: -0.488) spanning 748 amino acids (82.37 kDa) with a pI of 6.35, lacking an N-terminal secretory signal peptide. For 3D modeling, both algorithms showed high structural convergence with pLDDT scores >90% in the core alpha-helical bundles. Stereochemical validation confirmed high reliability, with Ramachandran highly favored regions at 91.1% (AlphaFold2) and 91.7% (SWISS-MODEL), ERRAT scores around 97.0%, and Verify3D compatibility >91%. Both models identified a shared Lys305 outlier on a flexible peripheral loop. PyMOL successfully mapped the spatial organization of the conserved catalytic triad: Arginine-93 (R93) as the transition state stabilizer, Histidine-97 (H97) as the proton acceptor, and Histidine-270 (H270) as the axial heme-iron binding ligand.

Conclusion: The in silico findings reveal that T. marneffei KatG is an intracellular, highly stable enzyme structurally optimized for efficient catalytic electron transfer, providing crucial insights into the pathogen's primary molecular defense line against host oxidative stress.