Protein palmitoylation in Toxoplasma gondii

CORVI, MM; DE NAPOLI, MG; ALONSO, AM

Mar del Plata

Congreso; IX Congreso Argentino de Protozoologia y Enfermedades Parasitarias; 2011

Protein palmitoylation in Toxoplasma gondii Corvi MM, De Napoli MG, Alonso MA. Laboratorio de parasitología molecular. IIB-INTECH. Chascomús, provincia de Buenos Aires, Argentina.   Protein palmitoylation is a post-translational modification that refers to the reversible covalent attachment of long-chain fatty acids onto proteins generally via a thioester bond. Although palmitic acid (C16:0), is the most common fatty acid to be linked to proteins, other fatty acids can be attached in this manner –both saturated and unsaturated fatty acids and these include myristic, oleic, arachidonic and stearic acids. The physiological importance of protein palmitoylation lays in the fact that, contrary to other lipid modifications, palmitoylation is reversible and as such can actively modulate the location and function of specific proteins. The target of this modification can be both cytosolic and transmembrane proteins. Protein palmitoylation is important for membrane anchoring, targeting of proteins to lipid rafts, trafficking proteins from the early secretory pathway to the plasma membrane, regulating protein activity and modulating the gene transcription of mitochondrial proteins. Although many aspects of protein palmitoylation have been identified in mammalian and yeast cells, little is known of this modification in Toxoplasma gondii (recently reviewed in [1]). In T. gondii, it has been reported that incubation of tachyzoites with the widely used palmitoylation inhibitor 2-bromopalmitate altered the parasite gliding motility and severely reduced the invasion to the host-cell. Gliding motility was altered by significant increase in non-circular trails and by the length of these trails that were longer than those left by non-treated parasites. Furthermore, 2-bromopalmitate treatment significantly reduced the invasion process to the host-cells. These results suggest that protein/s involved in gliding motility and invasion could be palmitoylated and that this modification seems to be necessary for an adequate regulation of these processes. In agreement with these results, many proteins involved in invasion are predicted to be palmitoylated [2](Table 1). Other proteins related to the IMC and/or the invasion processes that are predicted to be palmitoylated include IMC1 and TgHSP20. TgHSP20 is a chaperone localized to the IMC and its function is unknown yet. Our preliminary results indicate that this chaperone is palmitoylated and that this modification is responsible for its localization at the IMC. Recently, N-terminal myristoylation and palmitoylation have been reported to be responsible for membrane targeting of ISP1-3 (IMC-sub-compartment proteins) to the IMC [3]. Likewise HSP20, ISPs lack a predicted signal peptide or even a transmembrane domain. In addition to proteins that are found to be palmitoylated, T. gondii’s genome encodes for 17 DHHC-containing proteins –putative palmitoyl acyltransferases- that share homology with the human counterparts [1]. This suggests that T. gondii has the machinery required for protein palmitoylation to take place.             Protein palmitoylation in T. gondii is rising in significance. In fact, although few, all the work already published [4,5] suggest that this modification is of importance in granting appropriate membrane localization to the modified protein. As such, roles played by protein palmitoylation in T. gondii do not seem to be different than those observed in other eukaryotic cells (e.g. human or yeast). Unraveling the T. gondii palmitoyl proteome is certain to reveal the importance of this post-translational modification in the biology of this parasite.   Table 1: T. gondii predicted palmitoylated proteins involved in the invasion process   Name of protein TgME_gene ID* Cysteine position/s AMA1 TGME49_055260 3, 44 and 504 MIC2 TGME49_001780 2, 183, 185 and 564 MIC3 TGME49_119560 107, 263, 302 and 354 MIC4 TGME49_008030 12, 68, 261, 301 and 448 MIC7 TGME49_061780 38, 53, 215 and 290 MLC1 TGME49_057680 8, 11 and 205 RON4 TGME49_029010 20 ROP2A TGME49_015780 4 and 12   *Toxoplasma database version 7.0 (http://toxodb.org/toxo/)     References [1]        Corvi, M.M., Berthiaume, L.G. and Napoli, M.G. (2011). Protein palmitoylation in protozoan parasites. Front Biosci (Schol Ed) 3, 1067-79. [2]        Ren, J., Wen, L., Gao, X., Jin, C., Xue, Y. and Yao, X. (2008). CSS-Palm 2.0: an updated software for palmitoylation sites prediction. Protein Eng Des Sel 21, 639-44. [3]        Beck, J.R., Rodriguez-Fernandez, I.A., Cruz de Leon, J., Huynh, M.H., Carruthers, V.B., Morrissette, N.S. and Bradley, P.J. (2010). A novel family of Toxoplasma IMC proteins displays a hierarchical organization and functions in coordinating parasite division. PLoS Pathog 6 [4]        Donald, R.G. and Liberator, P.A. (2002). Molecular characterization of a coccidian parasite cGMP dependent protein kinase. Mol Biochem Parasitol 120, 165-75. [5]        Gilk, S.D., Gaskins, E., Ward, G.E. and Beckers, C.J. (2009). GAP45 phosphorylation controls assembly of the Toxoplasma myosin XIV complex. Eukaryot Cell 8, 190-6.