All eukaryotic cells express glycosylphosphatidylinositol (GPI)-anchored proteins. GPI-anchors are added post-transcriptionally by covalent linkage of a preassembled core anchor to the C-terminus of the protein. Whereas most eukaryotic cells express a number of GPI-anchored surface proteins in low abundance (mammalian cells express approx. 200 different proteins amounting to about 0.5 % of total cell surface proteins) the cell surface of African trypanosomes is dominated by a single GPI-anchored protein. We are utilizing this unusual abundance for the functional analysis of GPI-proteins.
The first two complete structures of GPI-anchors were reported in 1988. One structure was that of rat Thy-1, the other stemmed from the major surface protein of the bloodstream form of Trypanosoma brucei, the variant surface glycoprotein (VSG). Since then it has become clear that all GPI-anchors are composed of the same core structure, EtN-P-6Manα1-2Manα1-6Manα1-4GlcNα1-6myoInositol-phospholipid. The final composition of this anchor is modified by additions to the mannose moieties. The nature of these modifications and the attached lipids are governed by the species the protein is expressed in and by the protein itself. GPI-anchored proteins are attached to the cell surface via their lipid moieties and are therefore attached only to the outer leaflet of the plasma membrane. This gives GPI-anchored proteins unique characteristics compared to transmembrane proteins.
VSG structure (Thomas Bartossek)
The bloodstream form of African trypanosomes expresses a single GPI-anchored surface protein, the VSG, which accounts for more than 95% of total cell surface protein. The VSG is a glycoprotein and forms homodimers. In Trypanosoma brucei each monomer of around 45-55kDa consists of a larger N-terminal domain (350-400 residues) and a smaller C-terminal domain, which can contain either one or two structured domains (30-70 residues each). All structured domains are connected by flexible hinge regions.
The structures of the N-terminal domain of two different VSGs (MITat1.2 and ILTat1.24) have been solved by x-ray crystallography, and they are remarkably similar, despite their low sequence homology. Typically, there is less than 25% sequence similarity at the amino acid level between different VSGs, however, these proteins are all expected to adopt roughly the same folds. This VSG-fold appears to be required for the protective function of the surface coat, whereas the variation in primary sequence is the basis of antigenic variation.
In addition, the structures of the C-terminal domains of MITat1.2 and ILTat1.24 have been solved with the aid of NMR-spectroscopy. Whereas VSG MITat1.2 contains one structure domain in the C-terminal domain, ILTat1.24 contains two structured domains. All three solved C-terminal domain structures share a common core structure.
Although much is known about the protein structure and GPI-anchor of the VSG no structure of a complete VSG has been solved to date. Details of this project will be added upon publication.
VSG structure/function relationship (Erick Aroko)
The VSG is essential for the survival of African trypanosomes in the bloodstream of their mammalian host. It forms a densely packed coat on the surface of the trypanosome thereby protecting the underlying cell surface from the innate and adaptive immune responses of the host. The VSG itself is highly immunogenic, but at low antibody titres VSG bound antibodies are taken up by endocytosis and destroyed whereas the VSG is recycled to the cell surface. At higher antibody titres antigenic variation, whereby the cells switch from one expressed VSG to a different, antigenically distinct VSG allows the cells to thrive until a new immune response is raised by the host. The aim of this project is to gain a better understanding of the relationship of VSG structure with its function.
Details of this project will be added upon publication.
Diffusion of GPI-anchored proteins
he lateral mobility of a membrane protein, like its structure, is an essential determinant of the protein’s function. Yet, diffusion on a lipid bilayer is still not fully understood and contradictory results exist. We aim to systematically analyse the effect of domains exposed to the extracellular milieu on diffusion. We are using a parallel approach taking advantage of the unique properties of unicellular, parasitic African trypanosomes, which display a dense coat composed of one of a family of GPI-anchored proteins, the variant surface glycoprotein (VSG), on their cell surface at any one time. By employing an artificial lipid bilayer system we can measure diffusion under precisely defined experimental conditions, which will complement our in vivo experiments.
More details of this project will be added upon publication.
Kerstin Fey, 2011
Thomas Bartossek, 2011
John Bührdel, 2010
Jasmin Henning, 2014
Frederik Helmprobst, 2013
Anastasija Specht, 2013
Carina Goos, 2013
Marius Glogger, 2013
Anica Maier, 2014
Benjamin Schleicher, 2013
Michael Götz, 2012
Jasmin Henning, 2012
Frederik Helmprobst, 2011
Anastasija Specht, 2011
List of Publications
Hartel, A.J.W., Glogger, M., Guigas, G., Jones, N.G., Fenz, S.F., Weiss, M., Engstler, M. (2015). The molecular size of the extra-membrane domain influences the diffusion of the GPI-anchored VSG on the trypanosome plasma membrane. Scientific Reports 5, 10394.
Batram, C., Jones, N.G., Janzen, C.J., Markert, S.M., Engstler, M. (2014). Expression site attenuation mechanistically links antigenic variation and development in Trypanosoma brucei. Elife 3, e02324.
Abuillan, W., Vorobiev, A., Hartel, A., Jones, N.G., Engstler, M., Tanaka, M. (2012). Quantitative determination of the lateral density and intermolecular correlation between proteins anchored on the membrane surfaces using grazing incidence small-angle X-ray scattering and grazing incidence X-ray fluorescence. The Journal of Chemical Physics 137, 204907.
Harrington, J.M., Scelsi, C., Hartel, A., Jones, N.G., Engstler, M., Capewell, P., MacLeod, A., Hajduk, S. (2012). Novel African Trypanocidal Agents: Membrane Rigidifying Peptides. PLoS ONE 7, e44384.
Hiltensperger, G., Jones, N.G., Niedermeier, S., Stich, A., Kaiser, M., Jung, J., Puhl, S., Damme, A., Braunschweig, H., Meinel, L., et al. (2012). Synthesis and Structure-Activity Relationships of New Quinolone-Type Molecules against Trypanosoma brucei. Journal of Medicinal Chemistry 55, 2538-2548.
Schwede, A., Jones, N., Engstler, M., and Carrington, M. (2011). The VSG C-terminal domain is inaccessible to antibodies on live trypanosomes. Molecular and Biochemical Parasitology 175, 201-204.
Field, M.C., Lumb, J.H., Adung’a, V.O., Jones, N.G., and Engstler, M. (2009). Macromolecular trafficking and immune evasion in African trypanosomes. International Review of Cell and Molecular Biology 278, 1-67.
Jones, N.G., Nietlispach, D., Sharma, R., Burke, D.F., Eyres, I., Mues, M., Mott, H.R., and Carrington, M. (2008). Structure of a glycosylphosphatidylinositol-anchored domain from a trypanosome variant surface glycoprotein. The Journal of Biological Chemistry 283, 3584-3593.
Marcello, L., Menon, S., Ward, P., Wilkes, J.M., Jones, N.G., Carrington, M., and Barry, J.D. (2007). VSGdb: a database for trypanosome variant surface glycoproteins, a large and diverse family of coiled coil proteins. BMC Bioinformatics 8, 143.
Hutchinson, O.C., Picozzi, K., Jones, N.G., Mott, H., Sharma, R., Welburn, S.C., and Carrington, M. (2007). Variant Surface Glycoprotein gene repertoires in Trypanosoma brucei have diverged to become strain-specific. BMC Genomics 8, 234.
Chattopadhyay, A., Jones, N.G., Nietlispach, D., Nielsen, P.R., Voorheis, H.P., Mott, H.R., and Carrington, M. (2005). Structure of the C-terminal domain from Trypanosoma brucei variant surface glycoprotein MITat1.2. The Journal of Biological Chemistry 280, 7228-7235.
Barry, J.D., Marcello, L., Morrison, L.J., Read, A.F., Lythgoe, K., Jones, N., Carrington, M., Blandin, G., Böhme, U., Caler, E., et al. (2005). What the genome sequence is revealing about trypanosome antigenic variation. Biochemical Society Transactions 33, 986-989.
Kamp, G., Busselmann, G., Jones, N., Wiesner, B., and Lauterwein, J. (2003). Energy metabolism and intracellular pH in boar spermatozoa. Reproduction (Cambridge, England) 126, 517-525.
Hutchinson, O.C., Smith, W., Jones, N.G., Chattopadhyay, A., Welburn, S.C., and Carrington, M. (2003). VSG structure: similar N-terminal domains can form functional VSGs with different types of C-terminal domain. Molecular and Biochemical Parasitology 130, 127-131.
Bone, W., Jones, N.G., Kamp, G., Yeung, C.H., and Cooper, T.G. (2000). Effect of ornidazole on fertility of male rats: inhibition of a glycolysis-related motility pattern and zona binding required for fertilization in vitro. Journal of Reproduction and Fertility 118, 127-135.