Structural Characterization of the Type IV Secretion System in Brucella melitensis for Virtual Screening-Based Therapeutic Targeting

Brucellosis is a globally important zoonotic disease caused by Brucella melitensis, the most virulent and clinically significant species affecting both humans and livestock. Unlike many Gram-negative pathogens, B. melitensis lacks conventional virulence factors and instead relies on specialized systems such as the Type IV Secretion System (T4SS) for the secretion of effector proteins. In this study, an integrated computational pipeline was implemented to identify, model, and assemble the T4SS components encoded by virB operon from the complete B. melitensis proteome. Template-based modeling strategies were employed to model T4SS subcomplexes, referencing crystallographic data from E. coli T4SS. Structural superposition with E. coli homologues revealed highly conserved architecture despite only 30–50% sequence identity. Stereochemical validation confirmed favorable interactions among most VirB protein pairs, and membrane insertion analysis corroborated the spatial orientation of the modeled T4SS. Potential of T4SS as a drug target was explored by targeting dimeric interface of VirB11 ATPase to disrupt protein–protein interactions. Virtual screening of compounds from DrugBank revealed compounds with docking score ≤−7.0 kcal/mol, and ADMET screening yielded three promising candidates─Ezetimibe (Drug ID: DB00973), Chlordiazepoxide (Drug ID: DB00475), and Alloin (Drug ID: DB15477). MM-GBSA analysis and molecular dynamics simulation supported favorable protein–ligand interactions. Collectively, these findings provide new insights into the architecture of B. melitensis T4SS and identify three potential drug molecules targeting T4SS. This supports FDA-approved drug repurposing as an effective strategy for antivirulence therapy against Brucellosis.