Tracy Palmer - Biography#

Tracy Palmer has published 170 peer reviewed papers, with current h-index of 74 and 17997 citations (GoogleScholar, Jan 2025). She has made outstanding contributions to understanding protein secretion in bacteria. Tracy was one of the discoverers of the Tat pathway. Its most remarkable feature is the ability to transport folded proteins (up to 60Å diameter) across the ionically-tight bacterial cytoplasmic membrane while maintaining impermeability to ions. Tracy has published more papers on the Tat system than any other researcher. Her group has been at the heart of studies to characterize the essential components of the Tat machinery and the mechanism of Tat transport. Her work has defined the topological organization and multimeric state of the TatABC components through a combination of genetics, biochemistry and fine-mapping crosslinking analysis. Tracy’s group have also worked extensively on Tat signal peptides, collaborating with a bioinformatics group to test programs for the recognition of Tat targeting signals. She has developed numerous Tat-dependent reporter systems for validation of Tat transport. Her work with Gram-positive Streptomyces coelicolor showed that the Tat pathway is a major route of protein export, transporting in excess of 100 Tat substrates in this organism, and she has identified completely novel classes of membrane proteins requiring the concerted action of both Sec and Tat pathways for assembly.

Tracy has also made important discoveries on the type VII secretion system (T7SS) of Firmicutes, using Staphylococcus aureus as a model. She identified EsaD as a T7 substrate of S. aureus, showing that it has a C-terminal nuclease domain and that it kills closely related bacteria. This was a key discovery because it was the first demonstration that the T7SS is involved in interbacterial competition . Her group purified a pre-secretion complex of EsaD with its immunity protein and chaperone, identifying a further three small helical partner proteins. These helical partners bind to the EsaD N-terminus to form a composite signal for targeting to the T7SS . She later identified the TspA substrate, showing that it has a C-terminal membrane-depolarizing domain with a primary role bacterial antagonism. Her work has characterised a second membrane-depolarising T7 toxin, EsxX, showing that unexpectedly it has toxicity from either side of the membrane. Accordingly, different families of immunity proteins are required for its neutralisation depending on the cellular location of the toxin. Her group identified the first ‘reverse’ T7 substrate, TslA, an antibacterial lipase toxin that has an unexpected reverse domain arrangement, defining a new class of T7SS substrate protein.

Tracy has served on national and international boards and for many organizations, currently serving as Member of the EMBO Course Committee, the ERC Advanced Panel and the Scientific Council of Institut Pasteur.