HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Chloride intracellular channel protein 1 (CLIC1) functions as an anion channel in plasma and nuclear membranes when its soluble monomeric form converts to an integral-membrane form. The transmembrane region of CLIC1 is located in its thioredoxin-like domain 1 but the mechanism whereby the protein converts to its membrane conformation has yet to be determined. Since channel formation in membranes is enhanced at low pH (5 to 5.5), a condition that is found at the surface of membranes, the structural dynamics of soluble CLIC1 was studied at pH 7 and at pH 5.5 in the absence of membranes by amide hydrogen-deuterium exchange mass spectrometry (DXMS). Rapid hydrogen exchange data indicate that CLIC1 displays a similar core structure at these pH values. Domain 1 is less stable than the all-helical domain 2 and, while the structure of domain 1 remains intact, its conformational flexibility is further increased in an acidic environment (pH 5.5). In the absence of membrane, an acidic environment appears to prime the solution structure of CLIC1 by destabilising domain 1 in order to lower the activation energy barrier for its conversion to the membrane-insertion conformation. The significantly enhanced H/D-exchange rates at pH 5.5 displayed by two segments (peptides 11-31 and 68-82) could be due to the protonation of acidic residues in salt bridges. One of these segments (peptide 11-31) includes part of the transmembrane region which, in the solution structure, consists of helix α1. This helix is intrinsically stable and is most likely retained in the membrane conformation. Strand β2, another element of the transmembrane region, displays a propensity to form a helical structure and has putative N-and C-capping motifs, suggesting that it too most likely forms a helix in a lipid bilayer.

Broadly neutralising antibodies (bNAbs) against human immunodeficiency virus type 1 (HIV-1), such as CAP256-VRC26 are being developed for HIV prevention and treatment. These Abs carry a unique but crucial post-translational modification (PTM), namely O-sulfated tyrosine in the heavy chain complementarity determining region (CDR) H3 loop. Several studies have demonstrated that plants are suitable hosts for the generation of highly active anti-HIV-1 antibodies with the potential to engineer PTMs. Here we report the expression and characterisation of CAP256-VRC26 bNAbs with posttranslational modifications (PTM). Two variants, CAP256-VRC26 (08 and 09) were expressed in glycoengineered Nicotiana benthamiana plants. By in planta co-expression of tyrosyl protein sulfotransferase 1, we installed O-sulfated tyrosine in CDR H3 of both bNAbs. These exhibited similar structural folding to the mammalian cell produced bNAbs, but non-sulfated versions showed loss of neutralisation breadth and potency. In contrast, tyrosine sulfated versions displayed equivalent neutralising activity to mammalian produced antibodies retaining exceptional potency against some subtype C viruses. Together, the data demonstrate the enormous potential of plant-based systems for multiple posttranslational engineering and production of fully active bnAbs for application in passive immunisation or as an alternative for current HiV/AiDS antiretroviral therapy regimens.

Phosphopeptide enrichment is an essential step in large-scale, quantitative phosphoproteomics by mass spectrometry. Several phosphopeptide affinity enrichment techniques exist, such as Immobilized Metal ion Affinity Chromatography (IMAC) and Metal Oxide Affinity Chromatography (MOAC). We compared Zirconium(IV) IMAC (Zr-IMAC) magnetic microparticles to more commonly used Titanium(IV) IMAC (Ti-IMAC) and TiO2 magnetic microparticles for phosphopeptide enrichment from simple and complex protein samples prior to phosphopeptide sequencing and characterization by mass spectrometry (LC-MS/MS). We optimized sample-loading conditions to increase phosphopeptide recovery for Zr-IMAC, Ti-IMAC and TiO2 based workflows by 22%, 24% and 35% respectively. The optimized protocol resulted in improved performance of Zr-IMAC over Ti-IMAC and TiO2 as well as HPLC-based Fe(III)-IMAC with up to 23% more identified phosphopeptides. The different enrichment chemistries showed a high degree of overlap but also differences in phosphopeptide selectivity and complementarity. We conclude that Zr-IMAC improves phosphoproteome coverage and recommend that this complementary and scalable affinity enrichment method is more widely used in biological and biomedical studies of cell signaling and the search for biomarkers. Data are available via ProteomeXchange with identifier PXD018273.

BackgroundPlasmodium falciparum, the causative agent of severe human malaria, has evolved to become resistant to previously successful antimalarial chemotherapies, most notably chloroquine and the antifolates. The prevalence of resistant strains has necessitated the discovery and development of new chemical entities with novel modes-of-action. Although much effort has been invested in the creation of analogues based on existing drugs and the screening of chemical and natural compound libraries, a crucial shortcoming in current Plasmodial drug discovery efforts remains the lack of an extensive set of novel, validated drug targets. A requirement of these targets (or the pathways in which they function) is that they prove essential for parasite survival. The polyamine biosynthetic pathway, responsible for the metabolism of highly abundant amines crucial for parasite growth, proliferation and differentiation, is currently under investigation as an antimalarial target. Chemotherapeutic strategies targeting this pathway have been successfully utilized for the treatment of Trypanosomes causing West African sleeping sickness. In order to further evaluate polyamine depletion as possible antimalarial intervention, the consequences of inhibiting P. falciparum spermidine synthase (PfSpdSyn) were examined on a morphological, transcriptomic, proteomic and metabolic level.ResultsMorphological analysis of P. falciparum 3D7 following application of the PfSpdSyn inhibitor cyclohexylamine confirmed that parasite development was completely arrested at the early trophozoite stage. This is in contrast to untreated parasites which progressed to late trophozoites at comparable time points. Global gene expression analyses confirmed a transcriptional arrest in the parasite. Several of the differentially expressed genes mapped to the polyamine biosynthetic and associated metabolic pathways. Differential expression of corresponding parasite proteins involved in polyamine biosynthesis was also observed. Most notably, uridine phosphorylase, adenosine deaminase, lysine decarboxylase (LDC) and S-adenosylmethionine synthetase were differentially expressed at the transcript and/or protein level. Several genes in associated metabolic pathways (purine metabolism and various methyltransferases) were also affected. The specific nature of the perturbation was additionally reflected by changes in polyamine metabolite levels.ConclusionsThis study details the malaria parasite's response to PfSpdSyn inhibition on the transcriptomic, proteomic and metabolic levels. The results corroborate and significantly expand previous functional genomics studies relating to polyamine depletion in this parasite. Moreover, they confirm the role of transcriptional regulation in P. falciparum, particularly in this pathway. The findings promote this essential pathway as a target for antimalarial chemotherapeutic intervention strategies.