This research seeks to understand the fundamental process of protein translocation across membrane barriers in bacteria. To establish an infection or exchange antibiotic resistance genes, bacteria must transport macromolecules across multiple membrane barriers: their own and the host cells. In response to the universal requirement for macromolecule export, bacteria have evolved elaborate machines called secretion systems that use energy to move macromolecules across membranes. The Durie lab focuses on the Type IV secretion system (T4SS). This family is unique in that there are T4SSs that can transport nucleic acid and/or protein cargo. We investigate the defect in organelle trafficking/intracellular multiplication (Dot/Icm) T4SS in Legionella pneumophila. This system is essential for pathogenesis, which results in the potentially fatal pneumonia Legionnaires’ disease. The Dot/Icm T4SS is composed of over 30 proteins and secretes over 300 protein substrates to evade the host cell’s immune system and scavenge nutrients. This represents a much larger repertoire of substrates than observed in other secretion systems. Our lab combines high-resolution structure determination by cryo-EM with thermodynamics and enzyme kinetics studies. These approaches complement traditional genetic and cell biological strategies and will lead to mechanistic insights into how this secretion system transports protein. Recent advances by others include a high-resolution structure of the core complex, spanning from the inner to the outer membrane. Still, important regions of the complex were not visualized in that work, including the periplasmic collar, the inner membrane complex, and the coupling complex, leaving gaps in our understanding of the structure and function of this complicated machinery. To capture an effector-engaged complex, we combine the above approaches to determine which of the many effectors is ideal for a poison domain construct to trap the complex in the state of translocation.
Zehra et al. (2026) studied this question.