Protein N-myristoylation is a 14-carbon fatty-acid modification that is conserved across eukaryotic species and occurs on nearly 1% of the cellular proteome1,2. The ability of the myristoyl group to facilitate dynamic protein–protein and protein–membrane interactions (known as the myristoyl switch) makes it an essential feature of many signal transduction systems3. Thus pathogenic strategies that facilitate protein demyristoylation would markedly alter the signalling landscape of infected host cells. Here we describe an irreversible mechanism of protein demyristoylation catalysed by invasion plasmid antigen J (IpaJ), a previously uncharacterized Shigella flexneri type III effector protein with cysteine protease activity. A yeast genetic screen for IpaJ substrates identified ADP-ribosylation factor (ARF)1p and ARF2p, small molecular mass GTPases that regulate cargo transport through the Golgi apparatus4. Mass spectrometry showed that IpaJ cleaved the peptide bond between N-myristoylated glycine-2 and asparagine-3 of human ARF1, thereby providing a new mechanism for host secretory inhibition by a bacterial pathogen5,6. We further demonstrate that IpaJ cleaves an array of N-myristoylated proteins involved in cellular growth, signal transduction, autophagasome maturation and organelle function. Taken together, these findings show a previously unrecognized pathogenic mechanism for the site-specific elimination of N-myristoyl protein modification.

Preeclampsia is a heterogeneous syndrome affecting 3–5% of all pregnancies. An imbalance of the anti and pro-angiogenic factors, soluble receptor fms-like tyrosine kinase 1 (sFLT1) and placental growth factor (PGF), are thought to contribute to the pathophysiology of preeclampsia. Maternal plasma PGF and sFLT1 were quantified by specific immunoassays in cross-sectional samples from 130 preeclamptic subjects and 342 normotensive controls at delivery, and longitudinally in samples from 50 women who developed preeclampsia and 250 normotensive controls. Among women who developed preeclampsia, 46% (n=23) evidenced a pattern of consistently low maternal PGF across pregnancy below the lower 95%CI of controls from 15 weeks gestation to term. In contrast, the remaining 54% (n=27) women who developed preeclampsia had maternal PGF concentrations similar to or above (n=7) those of normotensive controls. Subjects with low PGF across pregnancy who developed preeclampsia evidenced significantly higher blood pressure in early pregnancy (p<0.05), and after diagnosis, earlier gestational age at delivery (p<0.05), and more preterm birth (p<0.05) compared to preeclamptic patients with high PGF. A significant subset of women who develop preeclampsia evidence consistently low PGF across pregnancy. Low PGF with preeclampsia was associated with preterm delivery compared to preeclamptic patients with high PGF. Identifying women with consistently low plasma PGF during pregnancy may provide a greater understanding of preeclampsia pathophysiology, and may provide more focused research and clinical activities.

Circulating endothelial progenitor cells (EPCs) may contribute to vascular endothelial cell homeostasis, and low levels of these cells are predictive of cardiovascular disease. We hypothesized that circulating EPCs increase in number during uncomplicated pregnancy but are reduced in women with preeclampsia. Peripheral blood was obtained from pregnant women and from nulligravidas in cross-sectional design. Cells expressing CD34 or CD133, in combination with vascular endothelial growth factor receptor-2 (VEGFR-2), were enumerated by flow cytometry. Both CD34 + VEGFR-2 + (doubly positive) and CD133 + VEGFR-2 + cells were significantly increased during the second and third trimesters of uncomplicated pregnancy compared to the first trimester. First trimester and nulligravida groups did not differ. Endothelial progenitor cells, quantified by flow cytometry or by circulating angiogenic cell (CAC) culture assay, were significantly reduced in women with preeclampsia compared to third trimester controls. Circulating EPCs appear to increase during normal pregnancy, and comparatively reduced numbers of these cells exist during preeclampsia.