Only two trypanosome subspecies are able to cause human African trypanosomiasis. To establish an infection in human blood, they must overcome the innate immune system by resisting the toxic effects of trypanolytic factor 1 and trypanolytic factor 2 (refs. 1,2). These lipoprotein complexes contain an active, pore-forming component, apolipoprotein L1 (ApoL1), that causes trypanosome cell death3. One of the two human-infective subspecies, Trypanosoma brucei rhodesiense, differs from non-infective trypanosomes solely by the presence of the serum resistance-associated protein, which binds directly to ApoL1 and blocks its pore-forming capacity3,4,5. Since this interaction is the single critical event that renders T. b. rhodesiense human- infective, detailed structural information that allows identification of binding determinants is crucial to understand immune escape by the parasite. Here, we present the structure of serum resistance-associated protein and reveal the adaptations that occurred as it diverged from other trypanosome surface molecules to neutralize ApoL1. We also present our mapping of residues important for ApoL1 binding, giving molecular insight into this interaction at the heart of human sleeping sickness.
Subscribe to Journal
Get full journal access for 1 year
only $9.92 per issue
All prices are NET prices.
VAT will be added later in the checkout.
Tax calculation will be finalised during checkout.
Rent or Buy article
Get time limited or full article access on ReadCube.
All prices are NET prices.
Rifkin, M. R. Identification of the trypanocidal factor in normal human serum: high density lipoprotein. Proc. Natl Acad. Sci. USA 75, 3450–3454 (1978).
Tomlinson, S. et al. High-density-lipoprotein-independent killing of Trypanosoma brucei by human serum. Mol. Biochem. Parasitol. 70, 131–138 (1995).
Vanhamme, L. et al. Apolipoprotein L-I is the trypanosome lytic factor of human serum. Nature 422, 83–87 (2003).
Xong, H. V. et al. A VSG expression site-associated gene confers resistance to human serum in Trypanosoma rhodesiense. Cell 95, 839–846 (1998).
Lecordier, L. et al. C-terminal mutants of apolipoprotein L-I efficiently kill both Trypanosoma brucei brucei and Trypanosoma brucei rhodesiense. PLoS Pathog. 5, e1000685 (2009).
Greene, A. S. & Hajduk, S. L. Trypanosome lytic factor-1 initiates oxidation-stimulated osmotic lysis of Trypanosoma brucei brucei. J. Biol. Chem. 291, 3063–3075 (2016).
Molina-Portela, M. P., Samanovic, M. & Raper, J. Distinct roles of apolipoprotein components within the trypanosome lytic factor complex revealed in a novel transgenic mouse model. J. Exp. Med. 205, 1721–1728 (2008).
Thomson, R. & Finkelstein, A. Human trypanolytic factor APOL1 forms pH-gated cation-selective channels in planar lipid bilayers: relevance to trypanosome lysis. Proc. Natl Acad. Sci. USA 112, 2894–2899 (2015).
Molina-Portela Mdel, P., Lugli, E. B., Recio-Pinto, E. & Raper, J. Trypanosome lytic factor, a subclass of high-density lipoprotein, forms cation-selective pores in membranes. Mol. Biochem. Parasitol. 144, 218–226 (2005).
Oli, M. W., Cotlin, L. F., Shiflett, A. M. & Hajduk, S. L. Serum resistance-associated protein blocks lysosomal targeting of trypanosome lytic factor in Trypanosoma brucei. Eukaryot. Cell 5, 132–139 (2006).
Hager, K. M. et al. Endocytosis of a cytotoxic human high density lipoprotein results in disruption of acidic intracellular vesicles and subsequent killing of African trypanosomes. J. Cell Biol. 126, 155–167 (1994).
Perez-Morga, D. et al. Apolipoprotein L-I promotes trypanosome lysis by forming pores in lysosomal membranes. Science 309, 469–472 (2005).
Vanwalleghem, G. et al. Coupling of lysosomal and mitochondrial membrane permeabilization in trypanolysis by APOL1. Nat. Commun. 6, 8078 (2015).
Rifkin, M. R. Trypanosoma brucei: biochemical and morphological studies of cytotoxicity caused by normal human serum. Exp. Parasitol. 58, 81–93 (1984).
Campillo, N. & Carrington, M. The origin of the serum resistance associated (SRA) gene and a model of the structure of the SRA polypeptide from Trypanosoma brucei rhodesiense. Mol. Biochem Parasitol. 127, 79–84 (2003).
Stephens, N. A. & Hajduk, S. L. Endosomal localization of the serum resistance-associated protein in African trypanosomes confers human infectivity. Eukaryot. Cell 10, 1023–1033 (2011).
Bart, J. M. et al. Localization of serum resistance-associated protein in Trypanosoma brucei rhodesiense and transgenic Trypanosoma brucei brucei. Cell Microbiol. 17, 1523–1535 (2015).
Pays, E., Vanhollebeke, B., Uzureau, P., Lecordier, L. & Perez-Morga, D. The molecular arms race between African trypanosomes and humans. Nat. Rev. Microbiol. 12, 575–584 (2014).
Higgins, M. K. & Carrington, M. Sequence variation and structural conservation allows development of novel function and immune evasion in parasite surface protein families. Protein Sci. 23, 354–265 (2014).
Stodkilde, K., Torvund-Jensen, M., Moestrup, S. K. & Andersen, C. B. Structural basis for trypanosomal haem acquisition and susceptibility to the host innate immune system. Nat. Commun. 5, 5487 (2014).
Higgins, M. K. et al. Structure of the trypanosome haptoglobin-hemoglobin receptor and implications for nutrient uptake and innate immunity. Proc. Natl Acad. Sci. USA 110, 1905–1910 (2013).
Lane-Serff, H., MacGregor, P., Lowe, E. D., Carrington, M. & Higgins, M. K. Structural basis for ligand and innate immunity factor uptake by the trypanosome haptoglobin-haemoglobin receptor. eL ife 3, e05553 (2014).
Loveless, B. C. et al. Structural characterization and epitope mapping of the glutamic acid/alanine-rich protein from Trypanosoma congolense: defining assembly on the parasite cell surface. J. Biol. Chem. 286, 20658–20665 (2011).
Metcalf, P., Blum, M., Freymann, D., Turner, M. & Wiley, D. C. Two variant surface glycoproteins of Trypanosoma brucei of different sequence classes have similar 6 A resolution X-ray structures. Nature 325, 84–86 (1987).
Thomson, R. et al. Evolution of the primate trypanolytic factor APOL1. Proc. Natl Acad. Sci. USA 111, 2130–2139 (2014).
Li, M. Z. & Elledge, S. J. Harnessing homologous recombination in vitro to generate recombinant DNA via SLIC. Nat. Methods 4, 251–256 (2007).
Wang, Z. D. et al. Universal PCR amplification of mouse immunoglobulin gene variable regions: the design of degenerate primers and an assessment of the effect of DNA polymerase 3ʹ to 5ʹ exonuclease activity. J. Immunol. Methods 233, 167–177 (2000).
Fields, C. et al. Creation of recombinant antigen-binding molecules derived from hybridomas secreting specific antibodies. Nat. Protoc. 8, 1125–1148 (2013).
Walter, T. S. et al. Lysine methylation as a routine rescue strategy for protein crystallization. Structure 14, 1617–1622 (2006).
Kabsch, W. Xds. Acta Crystallogr. D. Biol. Crystallogr. 66, 125–132 (2010).
McCoy, A. J. et al. Phaser crystallographic software. J. Appl. Crystallogr. 40, 658–674 (2007).
Emsley, P., Lohkamp, B., Scott, W. G. & Cowtan, K. Features and development of Coot. Acta Crystallogr. D. 66, 486–501 (2010).
Adams, P. D. et al. PHENIX: a comprehensive Python-based system for macromolecular structure solution. Acta Crystallogr. D. 66, 213–221 (2010).
Bricogne, G. et al. BUSTER v.2.10.1. (Global Phasing Ltd., 2016).
Winn, M. D. et al. Overview of the CCP4 suite and current developments. Acta Crystallogr. Sect. D. 67, 235–242 (2011).
Murshudov, G. N., Vagin, A. A. & Dodson, E. J. Refinement of macromolecular structures by the maximum-likelihood method. Acta Crystallogr. D. 53, 240–55 (1997).
Konarev, P. V., Volkov, V. V., Sokolova, A. V., Koch, M. H. J. & Svergun, D. I. PRIMUS: a Windows PC-based system for small-angle scattering data analysis. J. Appl. Crystallogr. 36, 1277–1282 (2003).
Rambo, R. P. & Tainer, J. A. Accurate assessment of mass, models and resolution by small-angle scattering. Nature 496, 477–481 (2013).
Franke, D. & Svergun, D. I. DAMMIF, a program for rapid ab-initio shape determination in small-angle scattering. J. Appl. Crystallogr. 42, 342–346 (2009).
Pettersen, E. F. et al. UCSF chimera – a visualization system for exploratory research and analysis. J. Comput. Chem. 25, 1605–1612 (2004).
Podobnik, M. et al. Crystal structure of an invertebrate cytolysin pore reveals unique properties and mechanism of assembly. Nat. Commun. 7, 11598 (2016).
This work was supported by Wellcome Trust grant 093008/Z/10/Z and MRC grant MR/L008246/1. M.K.H. is a Wellcome Trust Investigator. We thank K. Gull and S. Dean for assistance with monoclonal antibody generation. We also thank the beamline scientists at Diamond Light Source beamline I03, BioSAXS P12 beamline EMBL Hamburg and D. Staunton for assistance with biophysics equipment. S.M. and C.V.R. acknowledge with thanks funding from a MRC programme grant (MR/N020413/1) and a Wellcome Trust Instrument Grant (WT 104923/Z/14/Z) for the HDX platform.
The authors declare no competing financial interests.
Publisher’s note: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
About this article
Cite this article
Zoll, S., Lane-Serff, H., Mehmood, S. et al. The structure of serum resistance-associated protein and its implications for human African trypanosomiasis. Nat Microbiol 3, 295–301 (2018). https://doi.org/10.1038/s41564-017-0085-3
Nature Microbiology (2021)