- Email: [email protected]
Plasmodium Protein Export at Higher PEXEL Resolution
Cell Host & Microbe
Previews Hofman, P., and Vouret-Craviari, V. (2012). Gut Microbes 3, 176–185.
Hondo, T., Kanaya, T., Takakura, I., Watanabe, H., Takahashi, Y., Nagasawa, Y., Terada, S., Ohwada, S., Watanabe, K., Kitazawa, H., et al. (2011). Am. J. Physiol. Gastrointest. Liver Physiol. 300, G442– G453.
Kanaya, T., Hase, K., Takahashi, D., Fukuda, S., Hoshino, K., Sasaki, I., Hemmi, H., Knoop, K.A., Kumar, N., Sato, M., et al. (2012). Nat. Immunol. 13, 729–736.
Owen, R.L., and Jones, A.L. (1974). Gastroenterology 66, 189–203.
Mahajan, A., Naylor, S., Mills, A.D., Low, J.C., Mackellar, A., Hoey, D.E., Currie, C.G., Gally, D.L., Huntley, J., and Smith, D.G. (2005). Cell Tissue Res. 321, 365–374.
Tahoun, A., Mahajan, S., Paxton, E., Malterer, G., Donaldson, D.S., Wang, W., Tan, A., Gillespie, T.L., O’Shea, M., Roe, A.J., et al. (2012). Cell Host Microbe 12, this issue, 645–656.
Savidge, T.C. 301–306.
(1996).
Trends
Microbiol.
4,
Plasmodium Protein Export at Higher PEXEL Resolution Daniel E. Goldberg1,* 1Howard Hughes Medical Institute, Departments of Medicine and Molecular Microbiology, Washington University School of Medicine, St. Louis, MO 63110-1093, USA *Correspondence: [email protected] http://dx.doi.org/10.1016/j.chom.2012.11.001
Intraerythrocytic malaria parasites send hundreds of effector proteins into the host cell. Diverse modes of export have been proposed for different proteins. In this issue, Gru¨ring et al. (2012) present findings that bring the models together. Malaria parasites export hundreds of proteins into the infected erythrocyte to commandeer the host cell (Maier et al., 2009). Doing so allows the organism to put variant antigens on the red cell surface for immune evasion and cytoadherence, enables it to set up new nutrient acquisition systems, dramatically changes the erythrocyte membrane and cytoskeleton for parasite survival and eventual egress, and probably effects changes yet to be discovered. Crucial to the export process, most of these mediators have a motif (RxLxE/Q/D) called the PEXEL, or Plasmodium export element, downstream of a signal sequence (Marti et al., 2004; Hiller et al., 2004). The fairly recent discovery that the PEXEL is cleaved after the conserved L (Chang et al., 2008) by an ER protease called plasmepsin V (Boddey et al., 2010; Russo et al., 2010) raised a conundrum: the targeting sequence is being cleaved off in the ER, but subsequently the protein must travel through the secretory system and find its way to the translocon at the parasite surface (de Koning-Ward et al. (2009) to be exported into the host cell. How does it do all this without its targeting sequence? Study of plasmepsin V yielded two observations
that bear on this. First, expression of a catalytically dead version of plasmepsin V acted in a dominant-negative fashion to block export, suggesting that plasmepsin V must interact with another critical component, possibly the chaperone Hsp101 (Russo et al., 2010). Second, an exported protein construct in which the PEXEL was deleted (preserving the signal peptide so that signal peptidase cleavage generated the same mature N terminus as did plasmepsin V with the intact protein) failed to be exported (Boddey et al., 2010). These results gave rise to two models (Goldberg and Cowman, 2010): in one, chaperones, perhaps including Hsp101, dock with plasmepsin V in the ER as the protease is cleaving off the PEXEL. The chaperones then guide the protein through the secretory system to the translocon at the parasite surface. The second model posits that plasmepsin V is located in subregions of the ER where it recognizes a PEXEL protein, cleaves it, and sends it through the secretory system in vesicles addressed to the translocon region of the surface. A third model has implicated the lipid PI3P in PEXEL recognition and targeting within the ER (Bhatta-
charjee et al., 2012). There are problems with all three models. For the first, how do Hsp101 and/or other chaperones get recycled? If a chaperone molecule or complex is needed for each molecule of exported protein, this is an enormous expense for the parasite and would lead to an accumulation of Hsp101 in the parasitophorous vacuole outside the parasite plasma membrane, for which evidence is lacking. Regarding the second model, there is no evidence that plasmepsin V is in a subregion of the ER (it appears to be diffusely distributed) or that a directed transport route exists from parts of the ER to parts of the parasite surface. For the third model, the data contradict findings in previous work, and the model has not been independently replicated. Also, PI3P binding to PEXELs does not correlate all that well with export, and complicated alternative routes are proposed for proteins that are exported even when the PEXEL is mutated. Additionally, PI3P binding to the PEXEL and cargo portage to ER exit sites must occur before plasmepsin V cleaves off the PEXEL, so plasmepsin V would have to be in a subregion. As mentioned before, there is no evidence for this.
Cell Host & Microbe 12, November 15, 2012 ª2012 Elsevier Inc. 609
Cell Host & Microbe
Previews
A second area of confusion a PEXEL, or conversely, how is that some exported prodoes the PEXEL bypass the teins do not possess a PEXEL need for a TM domain? What (so-called PNEPs, for PEXELis special about the TM negative exported proteins) domain of exported proteins? and may not be cleaved The data suggest that TM by plasmepsin V (Spielmann proteins are posttranslationand Gilberger, 2010). How ally inserted into their target do they get out? A third area membrane in the host cell, of uncertainty is that a numbut how is this achieved? ber of exported proteins More work of the quality of are membrane bound; some the present study will be have a PEXEL and some required to sort out the further do not. How do they get details of this special export exported? pathway. On this background, the paper by Gru¨ring et al. (2012) REFERENCES in this issue sheds some light Figure 1. Protein Export Model on the darkness. In a beauBhattacharjee, S., Stahelin, R.V., In the ER, a PEXEL protein is recognized by plasmepsin V in association with a Speicher, K.D., Speicher, D.W., tiful set of experiments, the membrane-associated chaperone complex that binds the mature N terminus and Haldar, K. (2012). Cell 148, after cleavage. The protein is brought to an export cargo receptor that authors show that any PNEP 201–212. recognizes the special TM domain of the chaperone complex and perhaps N terminus combined with the luminal chaperone bound to the N terminus. For a membrane protein, Boddey, J.A., Hodder, A.N., any PNEP transmembrane chaperones similarly recognize the N terminus and bring the protein to the Gu¨nther, S., Gilson, P.R., Patsiou(TM) domain is enough to ras, H., Kapp, E.A., Pearce, J.A., cargo receptor, which recognizes the protein’s own TM domain. Either type de Koning-Ward, T.F., Simpson, of protein now undergoes vesicular transport through the secretory system mediate export of a reporter. R.J., Crabb, B.S., and Cowman, to the plasma membrane, where a parasitophorous vacuole chaperone reThey go on to show that the A.F. (2010). Nature 463, 627–631. ceives the protein and hands it off to the translocon for export into the host cell. mature N termini of PEXEL Chang, H.H., Falick, A.M., Carlton, proteins (after PEXEL cleavP.M., Sedat, J.W., DeRisi, J.L., and age) are sufficient to mediate export nized by plasmepsin V, cleaved, and Marletta, M.A. (2008). Mol. Biochem. Parasitol. of the same reporter containing a PNEP handed to a chaperone complex at the 160, 107–115. TM sequence. Finally, they show that ER membrane, which recognizes the de Koning-Ward, T.F., Gilson, P.R., Boddey, J.A., membrane-bound exported proteins are mature N terminus. TM exported proteins Rug, M., Smith, B.J., Papenfuss, A.T., Sanders, inserted in the parasite plasma membrane are already attached to the membrane P.R., Lundie, R.J., Maier, A.G., Cowman, A.F., and Crabb, B.S. (2009). Nature 459, 945–949. before being unfolded and translocated to and are also recognized by chaperones. the parasitophorous vacuolar membrane The TM domain of the membrane protein Goldberg, D.E., and Cowman, A.F. (2010). Nat. at the parasite-erythrocyte boundary for or of the chaperone complex is recog- Rev. Microbiol. 8, 617–621. export into the host cell. nized by an export cargo receptor, which It is an occasion for rejoicing when new takes the protein out to the parasite Gru¨ring, C., Heiber, A., Kruse, F., Flemming, S., Franci, G., Colombo, S., Fasana, E., Scho¨ler, H., data make a problem seem simpler rather plasma membrane. There, chaperones in Borgese, N., Stunnenberg, H.G., et al. (2012). Cell than more complicated. This work sug- the parasitophorous vacuole take the still Host Microbe 12, this issue, 717–729. gests that, rather than being exceptions unfolded protein to the translocon and Hiller, N.L., Bhattacharjee, S., van Ooij, C., Liolios, to the rule, PNEPs are just exported hand it to Hsp101, which drives it through K., Harrison, T., Lopez-Estran˜o, C., and Haldar, K. proteins that have bypassed the need the channel into the erythrocyte. The (2004). Science 306, 1934–1937. for a PEXEL by using a special TM region. cargo receptor and chaperones would The work further suggests that transmem- recycle back to the ER. If the protein is Maier, A.G., Cooke, B.M., Cowman, A.F., and Tilley, L. (2009). Nat. Rev. Microbiol. 7, 341–354. brane exported proteins, rather than using induced to fold prematurely, it will either a completely different route from that be stuck in the plasma membrane (TM Marti, M., Good, R.T., Rug, M., Knuepfer, E., of soluble exported proteins, rely on the proteins) or dissociate from the chaper- and Cowman, A.F. (2004). Science 306, 1930– 1933. same mature N terminus and go through ones and float in the parasitophorous a similar soluble, unfolded stage. vacuole (soluble proteins). Russo, I., Babbitt, S., Muralidharan, V., Butler, T., We can now come up with new models This study opens up several new ques- Oksman, A., and Goldberg, D.E. (2010). Nature 463, 632–636. to explain the observations. One possible tions: How is the mature N terminus version is depicted in Figure 1. Newly recognized for export? How does the Spielmann, T., and Gilberger, T.-W. (2010). Trends synthesized PEXEL proteins are recog- PNEP TM domain bypass the need for Parasitol. 26, 6–10.
610 Cell Host & Microbe 12, November 15, 2012 ª2012 Elsevier Inc.
Previews Hofman, P., and Vouret-Craviari, V. (2012). Gut Microbes 3, 176–185.
Hondo, T., Kanaya, T., Takakura, I., Watanabe, H., Takahashi, Y., Nagasawa, Y., Terada, S., Ohwada, S., Watanabe, K., Kitazawa, H., et al. (2011). Am. J. Physiol. Gastrointest. Liver Physiol. 300, G442– G453.
Kanaya, T., Hase, K., Takahashi, D., Fukuda, S., Hoshino, K., Sasaki, I., Hemmi, H., Knoop, K.A., Kumar, N., Sato, M., et al. (2012). Nat. Immunol. 13, 729–736.
Owen, R.L., and Jones, A.L. (1974). Gastroenterology 66, 189–203.
Mahajan, A., Naylor, S., Mills, A.D., Low, J.C., Mackellar, A., Hoey, D.E., Currie, C.G., Gally, D.L., Huntley, J., and Smith, D.G. (2005). Cell Tissue Res. 321, 365–374.
Tahoun, A., Mahajan, S., Paxton, E., Malterer, G., Donaldson, D.S., Wang, W., Tan, A., Gillespie, T.L., O’Shea, M., Roe, A.J., et al. (2012). Cell Host Microbe 12, this issue, 645–656.
Savidge, T.C. 301–306.
(1996).
Trends
Microbiol.
4,
Plasmodium Protein Export at Higher PEXEL Resolution Daniel E. Goldberg1,* 1Howard Hughes Medical Institute, Departments of Medicine and Molecular Microbiology, Washington University School of Medicine, St. Louis, MO 63110-1093, USA *Correspondence: [email protected] http://dx.doi.org/10.1016/j.chom.2012.11.001
Intraerythrocytic malaria parasites send hundreds of effector proteins into the host cell. Diverse modes of export have been proposed for different proteins. In this issue, Gru¨ring et al. (2012) present findings that bring the models together. Malaria parasites export hundreds of proteins into the infected erythrocyte to commandeer the host cell (Maier et al., 2009). Doing so allows the organism to put variant antigens on the red cell surface for immune evasion and cytoadherence, enables it to set up new nutrient acquisition systems, dramatically changes the erythrocyte membrane and cytoskeleton for parasite survival and eventual egress, and probably effects changes yet to be discovered. Crucial to the export process, most of these mediators have a motif (RxLxE/Q/D) called the PEXEL, or Plasmodium export element, downstream of a signal sequence (Marti et al., 2004; Hiller et al., 2004). The fairly recent discovery that the PEXEL is cleaved after the conserved L (Chang et al., 2008) by an ER protease called plasmepsin V (Boddey et al., 2010; Russo et al., 2010) raised a conundrum: the targeting sequence is being cleaved off in the ER, but subsequently the protein must travel through the secretory system and find its way to the translocon at the parasite surface (de Koning-Ward et al. (2009) to be exported into the host cell. How does it do all this without its targeting sequence? Study of plasmepsin V yielded two observations
that bear on this. First, expression of a catalytically dead version of plasmepsin V acted in a dominant-negative fashion to block export, suggesting that plasmepsin V must interact with another critical component, possibly the chaperone Hsp101 (Russo et al., 2010). Second, an exported protein construct in which the PEXEL was deleted (preserving the signal peptide so that signal peptidase cleavage generated the same mature N terminus as did plasmepsin V with the intact protein) failed to be exported (Boddey et al., 2010). These results gave rise to two models (Goldberg and Cowman, 2010): in one, chaperones, perhaps including Hsp101, dock with plasmepsin V in the ER as the protease is cleaving off the PEXEL. The chaperones then guide the protein through the secretory system to the translocon at the parasite surface. The second model posits that plasmepsin V is located in subregions of the ER where it recognizes a PEXEL protein, cleaves it, and sends it through the secretory system in vesicles addressed to the translocon region of the surface. A third model has implicated the lipid PI3P in PEXEL recognition and targeting within the ER (Bhatta-
charjee et al., 2012). There are problems with all three models. For the first, how do Hsp101 and/or other chaperones get recycled? If a chaperone molecule or complex is needed for each molecule of exported protein, this is an enormous expense for the parasite and would lead to an accumulation of Hsp101 in the parasitophorous vacuole outside the parasite plasma membrane, for which evidence is lacking. Regarding the second model, there is no evidence that plasmepsin V is in a subregion of the ER (it appears to be diffusely distributed) or that a directed transport route exists from parts of the ER to parts of the parasite surface. For the third model, the data contradict findings in previous work, and the model has not been independently replicated. Also, PI3P binding to PEXELs does not correlate all that well with export, and complicated alternative routes are proposed for proteins that are exported even when the PEXEL is mutated. Additionally, PI3P binding to the PEXEL and cargo portage to ER exit sites must occur before plasmepsin V cleaves off the PEXEL, so plasmepsin V would have to be in a subregion. As mentioned before, there is no evidence for this.
Cell Host & Microbe 12, November 15, 2012 ª2012 Elsevier Inc. 609
Cell Host & Microbe
Previews
A second area of confusion a PEXEL, or conversely, how is that some exported prodoes the PEXEL bypass the teins do not possess a PEXEL need for a TM domain? What (so-called PNEPs, for PEXELis special about the TM negative exported proteins) domain of exported proteins? and may not be cleaved The data suggest that TM by plasmepsin V (Spielmann proteins are posttranslationand Gilberger, 2010). How ally inserted into their target do they get out? A third area membrane in the host cell, of uncertainty is that a numbut how is this achieved? ber of exported proteins More work of the quality of are membrane bound; some the present study will be have a PEXEL and some required to sort out the further do not. How do they get details of this special export exported? pathway. On this background, the paper by Gru¨ring et al. (2012) REFERENCES in this issue sheds some light Figure 1. Protein Export Model on the darkness. In a beauBhattacharjee, S., Stahelin, R.V., In the ER, a PEXEL protein is recognized by plasmepsin V in association with a Speicher, K.D., Speicher, D.W., tiful set of experiments, the membrane-associated chaperone complex that binds the mature N terminus and Haldar, K. (2012). Cell 148, after cleavage. The protein is brought to an export cargo receptor that authors show that any PNEP 201–212. recognizes the special TM domain of the chaperone complex and perhaps N terminus combined with the luminal chaperone bound to the N terminus. For a membrane protein, Boddey, J.A., Hodder, A.N., any PNEP transmembrane chaperones similarly recognize the N terminus and bring the protein to the Gu¨nther, S., Gilson, P.R., Patsiou(TM) domain is enough to ras, H., Kapp, E.A., Pearce, J.A., cargo receptor, which recognizes the protein’s own TM domain. Either type de Koning-Ward, T.F., Simpson, of protein now undergoes vesicular transport through the secretory system mediate export of a reporter. R.J., Crabb, B.S., and Cowman, to the plasma membrane, where a parasitophorous vacuole chaperone reThey go on to show that the A.F. (2010). Nature 463, 627–631. ceives the protein and hands it off to the translocon for export into the host cell. mature N termini of PEXEL Chang, H.H., Falick, A.M., Carlton, proteins (after PEXEL cleavP.M., Sedat, J.W., DeRisi, J.L., and age) are sufficient to mediate export nized by plasmepsin V, cleaved, and Marletta, M.A. (2008). Mol. Biochem. Parasitol. of the same reporter containing a PNEP handed to a chaperone complex at the 160, 107–115. TM sequence. Finally, they show that ER membrane, which recognizes the de Koning-Ward, T.F., Gilson, P.R., Boddey, J.A., membrane-bound exported proteins are mature N terminus. TM exported proteins Rug, M., Smith, B.J., Papenfuss, A.T., Sanders, inserted in the parasite plasma membrane are already attached to the membrane P.R., Lundie, R.J., Maier, A.G., Cowman, A.F., and Crabb, B.S. (2009). Nature 459, 945–949. before being unfolded and translocated to and are also recognized by chaperones. the parasitophorous vacuolar membrane The TM domain of the membrane protein Goldberg, D.E., and Cowman, A.F. (2010). Nat. at the parasite-erythrocyte boundary for or of the chaperone complex is recog- Rev. Microbiol. 8, 617–621. export into the host cell. nized by an export cargo receptor, which It is an occasion for rejoicing when new takes the protein out to the parasite Gru¨ring, C., Heiber, A., Kruse, F., Flemming, S., Franci, G., Colombo, S., Fasana, E., Scho¨ler, H., data make a problem seem simpler rather plasma membrane. There, chaperones in Borgese, N., Stunnenberg, H.G., et al. (2012). Cell than more complicated. This work sug- the parasitophorous vacuole take the still Host Microbe 12, this issue, 717–729. gests that, rather than being exceptions unfolded protein to the translocon and Hiller, N.L., Bhattacharjee, S., van Ooij, C., Liolios, to the rule, PNEPs are just exported hand it to Hsp101, which drives it through K., Harrison, T., Lopez-Estran˜o, C., and Haldar, K. proteins that have bypassed the need the channel into the erythrocyte. The (2004). Science 306, 1934–1937. for a PEXEL by using a special TM region. cargo receptor and chaperones would The work further suggests that transmem- recycle back to the ER. If the protein is Maier, A.G., Cooke, B.M., Cowman, A.F., and Tilley, L. (2009). Nat. Rev. Microbiol. 7, 341–354. brane exported proteins, rather than using induced to fold prematurely, it will either a completely different route from that be stuck in the plasma membrane (TM Marti, M., Good, R.T., Rug, M., Knuepfer, E., of soluble exported proteins, rely on the proteins) or dissociate from the chaper- and Cowman, A.F. (2004). Science 306, 1930– 1933. same mature N terminus and go through ones and float in the parasitophorous a similar soluble, unfolded stage. vacuole (soluble proteins). Russo, I., Babbitt, S., Muralidharan, V., Butler, T., We can now come up with new models This study opens up several new ques- Oksman, A., and Goldberg, D.E. (2010). Nature 463, 632–636. to explain the observations. One possible tions: How is the mature N terminus version is depicted in Figure 1. Newly recognized for export? How does the Spielmann, T., and Gilberger, T.-W. (2010). Trends synthesized PEXEL proteins are recog- PNEP TM domain bypass the need for Parasitol. 26, 6–10.
610 Cell Host & Microbe 12, November 15, 2012 ª2012 Elsevier Inc.