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outer membrane model. TpgA-N binding significantly enhanced resistance to membrane extraction, approximately doubling the peak force required compared with AtaA-TM alone. Structural analyses revealed that multiple electrostatic contacts at the AtaA-TM-TpgA-N interface collectively reinforce the complex under tensile loading. Furthermore, thermodynamic integration yielded a favorable restrained separation free energy, supporting stabilization of the complex. Because TpgA-N is a hydrophilic periplasmic protein, its translocation through the hydrophobic membrane core is energetically unfavorable. Thus, membrane extraction of AtaA-TM necessitates the prior dissociation of the stable AtaA-TM-TpgA-N interaction. Together, our results demonstrate that TpgA mechanically reinforces the membrane anchor of AtaA through both thermodynamic stabilization and increased resistance to tensile forces. This study highlights a specialized strategy where a periplasmic protein strengthens the membrane anchoring of giant bacterial adhesins to withstand environmental loads.
Sasahara et al. (Sun,) studied this question.