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Gram-negative bacteria are surrounded by two lipid bilayer membranes that protect and delineate the cytoplasm from the surrounding environment. These membranes are semi-permeable and only allow the diffusion of small molecules. Translocation of larger substrates, including proteins, across bacterial membranes requires the use of specialized nanomachines. These nanomachines are activated in response to specific environmental cues, allowing bacteria to transport molecules that will shape their local environment and promote their survival.
The type II secretion system
The type II secretion system (T2SS) is a nanomachine used by Gram-negative bacteria to transport large proteins in their native, active form from the periplasmic space to the outside environment. Substrates secreted by the T2SS, called exoproteins, are often toxins (such as cholera toxin) or a variety of enzymes that degrade macromolecules including DNA, lipids, proteins, carbohydrates or even man-made plastic. Although many T2SSs secrete multiple proteins, exoproteins do not have conserved linear secretion signals making their identification a challenge. Work in the laboratory is focused on studying the T2SSs from Klebsiella pneumoniae and pathogenic Escherichia coli with the goal of understanding the molecular mechanisms involved in protein secretion, the targets of secreted proteins and the underlying mechanisms that promote bacterial survival within their niche.
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