First Molecular-Level Model of the Chlamydia trachomatis Injectisome and Targeting CdsN ATPase Oligomerization for Antivirulence Therapy

Abstract

Chlamydia trachomatis is an obligate intracellular pathogen that causes sexually transmitted infections and trachoma. Its persistent forms show reduced antibiotic susceptibility, creating a need for new antivirulence strategies. The C. trachomatis injectisome or type III Secretion System (T3SS) injects effector proteins into host cells, yet the molecular structure of the complete apparatus is unknown. Here, we identify and validate all 13 T3SS constituent proteins using TXSSScan and reverse-BLAST analysis, and model and assemble them into the complete T3SS apparatus using an integrated computational pipeline. Template-based modeling revealed a conserved architecture despite low sequence identity (18-46%), and the assemblies were validated stereochemically and energetically against homolog controls. Targeting the oligomerization interface of the CdsN ATPase through structure-based virtual screening of the e-Drug3D and IMPPAT libraries, followed by ADMET filtering, including predicted membrane permeability for intracellular targeting, identified three repurposable FDA-approved candidates: M Roflumilast, Elacestrant, and Tecovirimat. MM-GBSA calculations and molecular dynamics simulations confirmed stable complexes with two adjacent CdsN monomers. Elacestrant showed the most favorable binding free energy. These results provide the first molecular-level map of the C. trachomatis T3SS and a rational basis for antivirulence drug repurposing. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=93 SRC="FIGDIR/small/723290v2_ufig1.gif" ALT="Figure 1"> View larger version (31K): org.highwire.dtl.DTLVardef@6893c8org.highwire.dtl.DTLVardef@1be5eddorg.highwire.dtl.DTLVardef@1462b25org.highwire.dtl.DTLVardef@1baadab_HPS_FORMAT_FIGEXP M_FIG C_FIG