RESUMO
Plasmodium falciparum, the causative agent of the deadliest form of human malaria, alternates expression of variable antigens, encoded by members of a multi-copy gene family named var. In var2csa, the var gene implicated in pregnancy-associated malaria, translational repression is regulated by a unique upstream open reading frame (uORF) found only in its 5' UTR. Here, we report that this translated uORF significantly alters both transcription and posttranslational protein trafficking. The parasite can alter a protein's destination without any modifications to the protein itself, but instead by an element within the 5' UTR of the transcript. This uORF-dependent localization was confirmed by single molecule STORM imaging, followed by fusion of the uORF to a reporter gene which changes its cellular localization from cytoplasmic to ER-associated. These data point towards a novel regulatory role of uORF in protein trafficking, with important implications for the pathology of pregnancy-associated malaria.
Assuntos
Antígenos de Protozoários/genética , Interações Hospedeiro-Parasita/genética , Malária Falciparum/parasitologia , Fases de Leitura Aberta/genética , Complicações Infecciosas na Gravidez/parasitologia , Regiões 5' não Traduzidas , Antígenos de Protozoários/metabolismo , Feminino , Humanos , Plasmodium falciparum/genética , Plasmodium falciparum/patogenicidade , Gravidez , Regiões Promotoras Genéticas , Transporte Proteico , Imagem Individual de Molécula/métodos , Fatores de Virulência/genética , Fatores de Virulência/metabolismoRESUMO
GTPases of immunity-associated proteins (GIMAPs) are regulators of lymphocyte survival and homeostasis. We previously determined the structural basis of GTP-dependent GIMAP2 scaffold formation on lipid droplets. To understand how its GTP hydrolysis is activated, we screened for other GIMAPs on lipid droplets and identified GIMAP7. In contrast to GIMAP2, GIMAP7 displayed dimerization-stimulated GTP hydrolysis. The crystal structure of GTP-bound GIMAP7 showed a homodimer that assembled via the G domains, with the helical extensions protruding in opposite directions. We identified a catalytic arginine that is supplied to the opposing monomer to stimulate GTP hydrolysis. GIMAP7 also stimulated GTP hydrolysis by GIMAP2 via an analogous mechanism. Finally, we found GIMAP2 and GIMAP7 expression differentially regulated in several human T cell lymphoma lines. Our findings suggest that GTPase activity in the GIMAP family is controlled by homo- and heterodimerization. This may have implications for the differential roles of some GIMAPs in lymphocyte survival.