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Following completion of my BSc in Biochemistry at the University of Leeds (1999), I worked as a research assistant in the group of Prof. P.J.F. Henderson (University of Leeds), focusing on the elucidation of structure/function relationship of bacterial membrane transporters. Inspired by the works in the field of membrane biochemistry, I started my PhD (2001) in the structural/functional characterisation of the GalP transporter from Escherichia coli. In the course of my doctorate studies, I had the pleasure to work with Prof. Stephen Baldwin (University of Leeds) and Prof. So Iwata (Imperial College London).
After submission of my PhD thesis (2004) I moved to Philipps University Marburg to work for Prof. Lars-Oliver Essen and the European Membrane Protein Concortium (e-MEP) on the development of medium-high throughput approaches for the cloning, expression, purification and crystallisation of integral membrane proteins from the genome of Helicobacter pylori (causative agent of ulcers and gastric cancer). In 2007, I embarked on my second Post-Doc in Justus-Liebig University Giessen, working for Prof. Jon Hughes in the elucidation of structure/function dynamics of cyanobacterial phytochromes (light-regulated histidine kinases).
From 2011 to 2013, I directed the laboratory of Prof. Lars-Oliver Essen in Philipps University and my work focused on the structural/functional characterisation of native and chemically engineered ion channels. I joined the department of Biological Sciences at the University of Huddersfield in 2013.
The main focus of my research is to investigate the structural changes that define the gating-behaviour of outer-membrane channels and to unravel the ways these structural/functional changes can regulate signalling cascades. Understanding of these relationships will enable the development of artificial channels with desired functionalities/characteristics for the generation of a new array of in vivo and in vitro biological tools. Currently, I focus on a) the chemical/biological engineering of the outer membrane protein G (OmpG) from E. coli and b) the biochemical and structural characterisation of Arabidopsis thaliana voltage dependent anion channels (VDACs).
Mertins, B., Psakis, G. and Essen, L. (2014) ‘VDAC: the wizard of mitochondrial OM’ Biological Chemistry , 395 (12), pp. 1435-1442. ISSN 1431-6730
Grosse, W., Psakis, G., Mertins, B., Reiss, P., Windisch, D., Brademann, F., B�rck, J., Ulrich, A., Koert, U. and Essen, L. (2014) ‘Structure-Based Engineering of a Minimal Porin Reveals Loop-Independent Channel Closure’ Biochemistry , 53 (29), pp. 4826-4838. ISSN 0006-2960
Sineshchekov, V., Mailliet, J., Psakis, G., Feilke, K., Kopycki, J., Zeidler, M., Essen, L. and Hughes, J. (2014) ‘Tyrosine 263 in Cyanobacterial Phytochrome Cph1 Optimizes Photochemistry at the prelumi-R?lumi-R Step’ Photochemistry and Photobiology , 90 (4), pp. 786-795. ISSN 00318655
Song, C., Psakis, G., Kopycki, J., Lang, C., Matysik, J. and Hughes, J. (2014) ‘The D-ring, Not the A-ring, Rotates in Synechococcus OS-B' Phytochrome’ Journal of Biological Chemistry , 289 (5), pp. 2552-2562. ISSN 0021-9258
Mertins, B., Psakis, G., Grosse, W., Back, K., Salisowski, A., Reiss, P., Koert, U. and Essen, L. (2012) ‘Flexibility of the N-Terminal mVDAC1 Segment Controls the Channels Gating Behavior’ PLoS ONE , 7 (10), p. e47938. ISSN 1932-6203
Song, C., Psakis, G., Lang, C., Mailliet, J., Zaanen, J., Gaertner, W., Hughes, J. and Matysik, J. (2011) ‘On the collective nature of phytochrome photoactivation’ Biochemistry , 50 (51), pp. 10987-10989. ISSN 0006-2960
Mailliet, J., Psakis, G., Feilke, K., Sineshchekov, V., Essen, L. and Hughes, J. (2011) ‘Spectroscopy and a high-resolution crystal structure of Tyr263 mutants of cyanobacterial phytochrome Cph1’ Journal of Molecular Biology , 413 (1), pp. 115-127. ISSN 0022-2836
Psakis, G., Mailliet, J., Lang, C., Teufel, L., Essen, L. and Hughes, J. (2011) ‘Signaling kinetics of cyanobacterial phytochrome Cph1, a light regulated histidine kinase’ Biochemistry , 50 (28), pp. 6178-6188. ISSN 0006-2960
Song, C., Psakis, G., Lang, C., Mailliet, J., Gaertner, W., Hughes, J. and Matysik, J. (2011) ‘Two ground state isoforms and a chromophore D-ring photoflip triggering extensive intramolecular changes in a canonical phytochrome’ Proceedings of the National Academy of Sciences , 108 (10), pp. 3842-3847. ISSN 00278424
Roeben, M., Hahn, J., Klein, E., Lamparter, T., Psakis, G., Hughes, J. and Schmieder, P. (2010) ‘NMR Spectroscopic Investigation of Mobility and Hydrogen Bonding of the Chromophore in the Binding Pocket of Phytochrome Proteins’ Chemical Physics and Physical Chemistry , 11 (6), pp. 1248-1257. ISSN 1439-7641
Mailliet, J., Psakis, G., Schroeder, C., Kaltofen, S., D�rrwang, U., Hughes, J. and Essen, L. (2009) ‘Dwelling in the dark: procedures for the crystallography of phytochromes and other photochromic proteins’ Acta Crystallographica Section D: Biological Crystallography , 65 (11), pp. 1232-1235. ISSN 1399-0047
Psakis, G., Polaczek, J. and Essen, L. (2009) ‘AcrB et al.: Obstinate contaminants in a picogram scale. One more bottleneck in the membrane protein structure pipeline’ Journal of Structural Biology , 166 (1), pp. 107-111. ISSN 1047-8477
Psakis, G., Saidijam, M., Shibayama, K., Polaczek, J., Bettaney, K., Baldwin, J., Baldwin, S., Hope, R., Essen, L., Essenberg, R. and Henderson, P. (2008) ‘The sodium-dependent D-glucose transport protein of Helicobacter pylori’ Molecular microbiology , 71 (2), pp. 391-403. ISSN 1365-2958
Patching, S., Psakis, G., Baldwin, S., Baldwin, J., Henderson, P. and Middleton, D. (2008) ‘Relative substrate affinities of wild-type and mutant forms of the Escherichia coli sugar transporter GalP determined by solid-state NMR’ Molecular Membrane Biology , 25 (6-7), pp. 474-484. ISSN 0968-7688 (print), 1464-5203 (electronic)
Psakis, G., Sandra, N., Holz, C., Kress, D., Maestre-Reyna, M., Polaczek, J., Illing, G. and Essen, L. (2007) ‘Expression screening of integral membrane proteins from Helicobacter pylori 26695’ Protein Science , 16 (12), pp. 2667-2676. ISSN 0961-8368
Saidijam, M., Bettaney, K., Szakonyi, G., Psakis, G., Shibayama, K., Suzuki, S., Clough, J., Blessie, V., Abbu-Bakr, A., Baumberg, S., Meuller, J., Hoyle, C., Palmer, S., Butaye, P., Walravens, K., Patching, S., O'reilly, J., Rutherford, N., Bill, R., Roper, D., Phillips-Jones, M. and Henderson, P. (2005) ‘Active membrane transport and receptor proteins from bacteria’ Biochemical Society Transactions , 33 (Pt 4), pp. 867-872. ISSN 0300-5127 (print), 1470-8752 (electronic)
Saidijam, M., Psakis, G., Clough, J., Meuller, J., Suzuki, S., Hoyle, C., Palmer, S., Morrison, S., Pos, M., Essenberg, R., Maiden, M., Abu-bakr, A., Baumberg, S., Neyfakh, A., Griffith, J., Stark, M., Ward, A., O'Reilly, J., Rutherford, N., Phillips-Jones, M. and Henderson, P. (2003) ‘Collection and characterisation of bacterial membrane proteins’ FEBS Letters , 555 (1), pp. 170-175. ISSN 0014-5793
Students who have government scholarships/studentships or are self-funded are welcome to apply for PhD positions in the following areas.
OmpG from E. coli forms a robust, yet non-selective, 14 β-sheeted pore and its monomeric nature makes it an ideal template for engineering. Loop flexibility has been shown to be critical for the gating characteristics of the majority of outer membrane proteins and channels. With a combination of chemical and biological approaches, artificial OmpG porins, harbouring either loops of various lengths and ion-affinities or soluble photo-activatable domains, can be constructed for the production of more selective or light-regulated channels, respectively.
VDACs are the most abundant mitochondrial outer membrane proteins, mediating, through their gating, the metabolite and ion exchange between mitochondria and other cellular compartments. Independently solved X-ray structures revealed an alignment of the N-terminal α-helix with the inner pore wall. It has been proposed that the flexibility of this helix is essential for the completion of the native channel open-to-closed state transitions and is potentially critical for intermolecular interactions with partners of anti- and pro-apoptotic cascades. Recently, five VDAC genes were identified in A. thaliana. AtVDAC1 appeared to be important for disease resistance through regulation of hydrogen peroxide generation, and AtVDACs 2 and 4 appeared to mediate various physiological functions such as leaf development, steady state of mitochondrial membrane potential, and pollen development. With their diverse functions and their putative involvement in plant programmed cell-death, elucidation of the structure/function relationship of plant VDACs and their in vitro characterisation is not only important for strengthening our understanding of "cell suicidal missions", but could also have an impact on biotechnological and agricultural research.