University of Dundee

Professor Tracy Palmer FRS FRSE FSB FAAM MEAM

Protein Transport in Bacteria
Professor of Molecular Microbiology
School of Life Sciences, University of Dundee, Dundee
Full Telephone: 
+44 (0) 1382 386464, int ext 86464


My group is interested in protein export pathways in bacteria, and our research covers two key areas, listed below. For information about our research please see my personal website.

1. The Tat pathway.

I have a long-standing interest the transport of proteins by the twin arginine protein transport pathway. This pathway, which is found in the cytoplasmic membranes of most bacteria, and the thylakoid membranes of plant chloroplasts, is highly unusual because it transports pre-folded proteins. Protein substrates are targeted to the Tat machinery by N-terminal signal peptides that contain an S/T-R-R-x-F-L-K ‘twin arginine’ motif. Our aims are to study the function and mechanism of the Tat protein transporter, and the contribution that it makes to the physiology of bacteria.

Functional studies on the bacterial Tat pathway are carried out in collaboration with Dr Ben Berks, University of Oxford. Using the model organism Escherichia coli, we have identified the tatA, tatB, tatC and tatE genes that encode components of the Tat system. Focusing on the major components, TatA, B and C we are studying their roles in protein transport by a combination of genetics, molecular biology and biochemical techniques.

Our physiological studies on the Tat pathway encompass the study of unusual Tat substrate proteins. Escherichia coli K12 has some 27 or so Tat substrates and about two thirds of these contain non-covalently bound redox cofactors that are bound prior to export by the Tat pathway. We collaborate with Professor Frank Sargent to genetically define the components required for the assembly of these complex Tat substrates before their interaction with the Tat system. 

2. The Type VII protein secretion system.

More recently we have become interested in the type VII protein secretion system (T7SS), primarily in the opportunistic human pathogen Staphylococcus aureus. Our structural and functional studies on this secretion machinery are undertaken collaboratively with Prof Bill Hunter (Division of Biological Chemistry and Drug Discovery). We are also interested in identifying and understanding the roles of secreted substrate proteins and how they contribute to virulence and interbacterial competition.


BI40051 - 4A05 Bacterial Membrane Biology

BI32052 Molecular Microbiology & Immunology


Casabona, M.G., Buchanan, G., Zoltner, M., Harkins, C.P., Holden, M.T.G. and Palmer, T. (2017) Functional analysis of the EsaB component of the Staphylococcus aureus Type VII secretion system. Microbiology. 163:1851–1863.

Casabona, M.G., Kneuper, H., Alferes de Lima, D., Harkins, C.P. Zoltner, M., Hjerde, E., Holden, M.T.G. and Palmer, T. (2017) Heme-iron plays a key role in the regulation of the Ess/Type VII secretion system of Staphylococcus aureus RN6390. Microbiology. 163:1839-1850.

Habersetzer, J., Moore, K., Cherry, J., Buchanan, G., Stansfeld, P.J. and Palmer, T. (2017) Substrate-triggered position switching of TatA and TatB during Tat transport in Escherichia coliOpen Biology7:170091.

Huang, Q and Palmer, T. (2017) Signal peptide hydrophobicity modulates interaction with the twin-arginine translocase. mBio 8, pii: e00909-17. doi: 10.1128/mBio.00909-17.

Tooke, F.J., Babot, M., Chandra, G., Buchanan, G. and Palmer, T. (2017) A unifying mechanism for the biogenesis of membrane proteins co-operatively integrated by the Sec and Tat pathways. eLife 6, pii: e26577. doi: 10.7554/eLife.26577

Lamont, C.M., Kelly, C.L., Pinske, C., Buchanan, G., Palmer, T. and Sargent F. (2017) Expanding the substrates for a bacterial hydrogenlyase reaction. Microbiology. 163, 649–653. In the press. doi: 10.1099/mic.0.000471

Palmer, T. (2017) Mycobacterial ESX secrets revealed. News and Views Article. Nature Microbiology 2, 17074. doi: 10.1038/nmicrobiol.2017.74

Huang, Q., Alcock, F., Kneuper, H., Deme, J.C., Rollauer, S.E. Lea, S.M., Berks, B.C. and Palmer, T. (2017) A signal sequence suppressor mutant that stabilizes an assembled state of the twin arginine translocase. Proceedings of the National Academy of Sciences USA.114, E1958-E1967.

Unnikrishnan, M., Constantinidou, C., Palmer, T. and Pallen, M. (2017) The enigmatic Esx proteins: looking beyond mycobacteria. Trends in Microbiology 25, 192-204.

Alcock, F., Stansfeld, P. J., Basit, H., Habersetzer, J., Baker, M. A., Palmer, T., Wallace, M. I. and Berks, B. C. (2016) Assembling the Tat protein translocase. eLife. 5

Cao, Z., Casabona, M. G., Kneuper, H., Chalmers, J. D. and Palmer, T. (2016) The type VII secretion system of Staphylococcus aureus secretes a nuclease toxin that targets competitor bacteria. Nature microbiology. 2, 16183

Jager, F., Zoltner, M., Kneuper, H., Hunter, W. N. and Palmer, T. (2016) Membrane interactions and self-association of components of the Ess/Type VII secretion system of Staphylococcus aureus. FEBS letters. 590, 349-357

Munnoch, J. T., Widdick, D. A., Chandra, G., Sutcliffe, I. C., Palmer, T. and Hutchings, M. I. (2016) Cosmid based mutagenesis causes genetic instability in Streptomyces coelicolor, as shown by targeting of the lipoprotein signal peptidase gene. Scientific reports. 6, 29495

Parthasarathy, S., Parapatla, H., Nandavaram, A., Palmer, T. and Siddavattam, D. (2016) Organophosphate Hydrolase Is a Lipoprotein and Interacts with Pi-specific Transport System to Facilitate Growth of Brevundimonas diminuta Using OP Insecticide as Source of Phosphate. The Journal of biological chemistry. 291, 7774-7785

Warne, B., Harkins, C. P., Harris, S. R., Vatsiou, A., Stanley-Wall, N., Parkhill, J., Peacock, S. J., Palmer, T. and Holden, M. T. (2016) The Ess/Type VII secretion system of Staphylococcus aureus shows unexpected genetic diversity. BMC genomics. 17, 222

Zoltner, M., Ng, W. M., Money, J. J., Fyfe, P. K., Kneuper, H., Palmer, T. and Hunter, W. N. (2016) EssC: domain structures inform on the elusive translocation channel in the Type VII secretion system. The Biochemical journal. 473, 1941-1952

Browning, D. F., Bavro, V. N., Mason, J. L., Sevastsyanovich, Y. R., Rossiter, A. E., Jeeves, M., Wells, T. J., Knowles, T. J., Cunningham, A. F., Donald, J. W., Palmer, T., Overduin, M. and Henderson, I. R. (2015) Cross-species chimeras reveal BamA POTRA and beta-barrel domains must be fine-tuned for efficient OMP insertion. Mol Microbiol. 97, 646-659

Cleon, F., Habersetzer, J., Alcock, F., Kneuper, H., Stansfeld, P. J., Basit, H., Wallace, M. I., Berks, B. C. and Palmer, T. (2015) The TatC component of the twin-arginine protein translocase functions as an obligate oligomer. Mol Microbiol. 98, 111-129

Kelly, C. L., Pinske, C., Murphy, B. J., Parkin, A., Armstrong, F., Palmer, T. and Sargent, F. (2015) Integration of an [FeFe]-hydrogenase into the anaerobic metabolism of. Biotechnology reports. 8, 94-104

McDowall, J. S., Hjersing, M. C., Palmer, T. and Sargent, F. (2015) Dissection and engineering of the Escherichia coli formate hydrogenlyase complex. FEBS Lett. 589, 3141-3147

Dow, J. M., Grahl, S., Ward, R., Evans, R., Byron, O., Norman, D. G., Palmer, T. and Sargent, F. (2014) Characterization of a periplasmic nitrate reductase in complex with its biosynthetic chaperone. The FEBS journal. 281, 246-260

Hamilton, J. J., Marlow, V. L., Owen, R. A., Costa Mde, A., Guo, M., Buchanan, G., Chandra, G., Trost, M., Coulthurst, S. J., Palmer, T., Stanley-Wall, N. R. and Sargent, F. (2014) A holin and an endopeptidase are essential for chitinolytic protein secretion in Serratia marcescens. J Cell Biol. 207, 615-626

Hopkins, A., Buchanan, G. and Palmer, T. (2014) Role of the twin arginine protein transport pathway in the assembly of the Streptomyces coelicolor cytochrome bc1 complex. J Bacteriol. 196, 50-59

Kneuper, H., Cao, Z. P., Twomey, K. B., Zoltner, M., Jager, F., Cargill, J. S., Chalmers, J., van der Kooi-Pol, M. M., van Dijl, J. M., Ryan, R. P., Hunter, W. N. and Palmer, T. (2014) Heterogeneity in ess transcriptional organization and variable contribution of the Ess/Type VII protein secretion system to virulence across closely related Staphylocccus aureus strains. Mol Microbiol. 93, 928-943

McDowall, J. S., Murphy, B. J., Haumann, M., Palmer, T., Armstrong, F. A. and Sargent, F. (2014) Bacterial formate hydrogenlyase complex. Proc Natl Acad Sci U S A. 111, E3948-3956

Alcock, F., Baker, M. A., Greene, N. P., Palmer, T., Wallace, M. I. and Berks, B. C. (2013) Live cell imaging shows reversible assembly of the TatA component of the twin-arginine protein transport system. Proc Natl Acad Sci U S A. 110, E3650-3659

Bowman, L., Palmer, T. and Sargent, F. (2013) A regulatory domain controls the transport activity of a twin-arginine signal peptide. FEBS Lett. 587, 3365-3370

Dow, J. M., Gabel, F., Sargent, F. and Palmer, T. (2013) Characterization of a pre-export enzyme-chaperone complex on the twin-arginine transport pathway. Biochem J. 452, 57-66

Fyans, J. K., Bignell, D., Loria, R., Toth, I. and Palmer, T. (2013) The ESX/type VII secretion system modulates development, but not virulence, of the plant pathogen Streptomyces scabies. Molecular plant pathology. 14, 119-130

James, M. J., Coulthurst, S. J., Palmer, T. and Sargent, F. (2013) Signal peptide etiquette during assembly of a complex respiratory enzyme. Mol Microbiol. 90, 400-414

Sargent, F., Davidson, F. A., Kelly, C. L., Binny, R., Christodoulides, N., Gibson, D., Johansson, E., Kozyrska, K., Lado, L. L., Maccallum, J., Montague, R., Ortmann, B., Owen, R., Coulthurst, S. J., Dupuy, L., Prescott, A. R. and Palmer, T. (2013) A synthetic system for expression of components of a bacterial microcompartment. Microbiology. 159, 2427-2436

Zoltner, M., Fyfe, P. K., Palmer, T. and Hunter, W. N. (2013) Characterization of Staphylococcus aureus EssB, an integral membrane component of the Type VII secretion system: atomic resolution crystal structure of the cytoplasmic segment. Biochem J. 449, 469-477

Zoltner, M., Norman, D. G., Fyfe, P. K., El Mkami, H., Palmer, T. and Hunter, W. N. (2013) The architecture of EssB, an integral membrane component of the type VII secretion system. Structure. 21, 595-603

Fritsch, M. J., Krehenbrink, M., Tarry, M. J., Berks, B. C. and Palmer, T. (2012) Processing by rhomboid protease is required for Providencia stuartii TatA to interact with TatC and to form functional homo-oligomeric complexes. Mol Microbiol. 84, 1108-1123

Keller, R., de Keyzer, J., Driessen, A. J. and Palmer, T. (2012) Co-operation between different argeting pathways during integration of a membrane protein. J Cell Biol. 199, 303-315

Kneuper, H., Maldonado, B., Jager, F., Krehenbrink, M., Buchanan, G., Keller, R., Muller, M., Berks, B. C. and Palmer, T. (2012) Molecular dissection of TatC defines critical regions essential for protein transport and a TatB-TatC contact site. Mol Microbiol. 85, 945-961

Koch, S., Fritsch, M. J., Buchanan, G. and Palmer, T. (2012) Escherichia coli TatA and TatB proteins have N-out, C-in topology in intact cells. J Biol Chem. 287, 14420-14431

Palmer, T. and Berks, B. C. (2012) The twin-arginine translocation (Tat) protein export pathway. Nature reviews. Microbiology. 10, 483-496

Parkin, A., Bowman, L., Roessler, M. M., Davies, R. A., Palmer, T., Armstrong, F. A. and Sargent, F. (2012) How Salmonella oxidises H(2) under aerobic conditions. FEBS Lett. 586, 536-544

Rollauer, S. E., Tarry, M. J., Graham, J. E., Jaaskelainen, M., Jager, F., Johnson, S., Krehenbrink, M., Liu, S. M., Lukey, M. J., Marcoux, J., McDowell, M. A., Rodriguez, F., Roversi, P., Stansfeld, P. J., Robinson, C. V., Sansom, M. S., Palmer, T., Hogbom, M., Berks, B. C. and Lea, S. M. (2012) Structure of the TatC core of the twin-arginine protein transport system. Nature. 492, 210-214

Willemse, J., Ruban-Osmialowska, B., Widdick, D., Celler, K., Hutchings, M. I., van Wezel, G. P. and Palmer, T. (2012) Dynamic localization of Tat protein transport machinery components in Streptomyces coelicolor. J Bacteriol. 194, 6272-6281