Solution characterization of TraW, a regulatory protein of the F plasmid type 4 secretion system

Bacterial conjugation facilitates horizontal gene transfer through the Type IV Secretion System (T4SS), a complex nanomachine central to antibiotic resistance dissemination. This study investigates the structure and dynamics of TraW, a key F-plasmid conjugative protein. TraW, in conjugation with the protein TrbC, is critical for F-pilus biogenesis and mating pair stabilization. Using biophysical, computational, and structural methods, including CD, NMR, SAXS, and native mass spectrometry, we characterize TraW as a modular protein with a stable C-terminal domain and a flexible N-terminal region. The full-length construct exhibits higher conformational adaptability and transient dimerization, whereas truncation enhances compactness and monomeric stability. AlphaFold modeling and SAXS analyses reveal that this flexibility, rather than intrinsic disorder, enables TraW to modulate inter-protein interactions essential for T4SS assembly and function. These findings establish TraW as a dynamic adaptor protein and highlight how flexibility fine-tunes structural plasticity in conjugative machinery.