Cécilia Eydoux

Further biochemical characterization of human pancreatic lipase-related protein 2 expressed in yeast cells

Recombinant human pancreatic lipase-related protein 2 (rHPLRP2) was produced in the protease A-deficient yeast Pichia pastoris. A major protein with a molecular mass of 50 kDa was purified from the culture medium using SP-Sepharose and Mono Q chromatography. The protein was found to be highly sensitive to the proteolytic cleavage of a peptide bond in the lid domain. The proteolytic cleavage process occurring in the lid affected both the lipase and phospholipase activities of rHPLRP2. The substrate specificity of the nonproteolyzed rHPLRP2 was investigated using pH-stat and monomolecular film techniques and various substrates (glycerides, phospholipids, and galactolipids). All of the enzyme activities were maximum at alkaline pH values and decreased in the pH 5–7 range corresponding to the physiological conditions occurring in the duodenum. rHPLRP2 was found to act preferentially on substrates forming small aggregates in solution (monoglycerides, egg phosphatidylcholine, and galactolipids) rather than on emulsified substrates such as triolein and diolein. The activity of rHPLRP2 on monogalactosyldiglyceride and digalactosyldiglyceride monomolecular films was determined and compared with that of guinea pig pancreatic lipase-related protein 2, which shows a large deletion in the lid domain. The presence of a full-length lid domain in rHPLRP2 makes it possible for enzyme activity to occur at higher surface pressures. The finding that the inhibition of nonproteolyzed rHPLRP2 by tetrahydrolipstatin and diethyl-p-nitrophenyl phosphate does not involve any bile salt requirements suggests that the rHPLRP2 lid adopts an open conformation in aqueous media.

Structure of human pancreatic lipase-related protein 2 with the lid in an open conformation.

Access to the active site of pancreatic lipase (PL) is controlled by a surface loop, the lid, which normally undergoes conformational changes only upon addition of lipids or amphiphiles. Structures of PL with their lids in the open and functional conformation have required cocrystallization with amphiphiles. Here we report two crystal structures of wild-type and unglycosylated human pancreatic lipase-related protein 2 (HPLRP2) with the lid in an open conformation in the absence of amphiphiles. These structures solved independently are strikingly similar, with some residues of the lid being poorly defined in the electron-density map. The open conformation of the lid is however different from that previously observed in classical liganded PL, suggesting different kinetic properties for HPLRP2. Here we show that the HPLRP2 is directly inhibited by E600, does not present interfacial activation, and acts preferentially on substrates forming monomers or small aggregates (micelles) dispersed in solution like monoglycerides, phospholipids and galactolipids, whereas classical PL displays reverse properties and a high specificity for unsoluble substrates like triglycerides and diglycerides forming oil-in-water interfaces. These biochemical properties imply that the lid of HPLRP2 is likely to spontaneously adopt in solution the open conformation observed in the crystal structure. This open conformation generates a large cavity capable of accommodating the digalactose polar head of galactolipids, similar to that previously observed in the active site of the guinea pig PLRP2, but absent from the classical PL. Most of the structural and kinetic properties of HPLRP2 were found to be different from those of rat PLRP2, the structure of which was previously obtained with the lid in a closed conformation. Our findings illustrate the essential role of the lid in determining the substrate specificity and the mechanism of action of lipases.

Antiviral chlorinated daphnane diterpenoid orthoesters from the bark and wood of Trigonostemon cherrieri

The chemical study of the bark and the wood of Trigonostemon cherrieri, a rare endemic plant of New Caledonia, led to the isolation of a series of highly oxygenated daphnane diterpenoid orthoesters (DDO) bearing an uncommon chlorinated moiety: trigocherrins A-F and trigocherriolides A-D. Herein, we describe the isolation and structure elucidation of the DDO (trigocherrins B-F and trigocherriolides A-D). We also report the antiviral activity of trigocherrins A, B and F (1, 2 and 6) and trigocherriolides A, B and C (7-9) against various emerging pathogens: chikungunya virus (CHIKV), Sindbis virus (SINV), Semliki forest virus (SFV) and dengue virus (DENV).

Alkylated Flavanones from the Bark of Cryptocarya chartacea As Dengue Virus NS5 Polymerase Inhibitors

An in vitro screening of New Caledonian plants allowed the selection of several species with a significant dengue virus NS5 RNA-dependent RNA polymerase (RdRp) inhibiting activity. The chemical investigation of Cryptocarya chartacea led to the isolation of a series of new mono- and dialkylated flavanones named chartaceones A-F (1-6), along with pinocembrin. They were isolated as racemic mixtures and characterized using extensive one- and two-dimensional NMR spectroscopy. Four diastereomers of chartaceone A (1) were separated using chiral HPLC, and their absolute configurations were established by comparison of their experimental and calculated ECD spectra. The dialkylated flavanones, chartaceones C-F (3-6), exhibited the most significant NS5 RdRp inhibiting activity, with IC(50) ranging from 1.8 to 4.2 μM. Chartaceones represent a new class of non-nucleosidic inhibitors of the DENV NS5 RdRp.

Chemical constituents of Anacolosa pervilleana and their antiviral activities.

In an effort to identify novel inhibitors of Chikungunya (CHIKV) and Dengue (DENV) virus replication, a systematic study with 820 ethyl acetate extracts of Madagascan plants was performed in a virus-cell-based assay for CHIKV and a DENV NS5 RNA-dependant RNA polymerase (RdRp) assay. The extract obtained from the leaves of Anacolosa pervilleana was selected for its significant activity in both assays. One new (E)-tridec-2-en-4-ynedioic acid named anacolosine (1), together with three known acetylenic acids, the octadeca-9,11,13-triynoic acid (2), (13E)-octadec-13-en-9,11-diynoic acid (3), (13E)-octadec-13-en-11-ynoic acid (4), two terpenoids, lupenone (5) and β-amyrone (6), and one cyanogenic glycoside, (S)-sambunigrin (7) were isolated. Their structures were elucidated by comprehensive analyses of NMR spectroscopy and mass spectrometry data. The inhibitory potency of these compounds was evaluated on CHIKV, DENV RdRp and West-Nile polymerase virus (WNV RdRp). Both terpenoids showed a moderate activity against CHIKV (EC(50) 77 and 86 μM, respectively) and the acetylenic acids produced IC(50) values around 3 μM in the DENV RdRp assay.

Flacourtosides A–F, Phenolic Glycosides Isolated from Flacourtia ramontchi

In an effort to identify novel inhibitors of chikungunya (CHIKV) and dengue (DENV) virus replication, a systematic study with 820 ethyl acetate extracts of madagascan plants was performed in a virus-cell-based assay for CHIKV, and a DENV NS5 RNA-dependent RNA polymerase (RdRp) assay. The extract obtained from the stem bark of Flacourtia ramontchi was selected for its significant activity in both assays. Six new phenolic glycosides, named flacourtosides A-F (1-6), phenolic glycosides itoside H, xylosmin, scolochinenoside D, and poliothrysoside, and betulinic acid 3β-caffeate were obtained using the bioassay-guided isolation process. Their structures were elucidated by comprehensive analyses of NMR spectroscopic and mass spectrometric data. Even though several extracts and fractions showed significant selective antiviral activity in the CHIKV virus-cell-based assay, none of the purified compounds did. However, in the DENV RNA polymerase assay, significant inhibition was observed with betulinic acid 3β-caffeate (IC(50) = 0.85 ± 0.1 μM) and to a lesser extent for the flacourtosides A and E (1 and 5, respectively), and scolochinenoside D (IC(50) values ~10 μM).

Biflavonoids of Dacrydium balansae with Potent Inhibitory Activity on Dengue 2 NS5 Polymerase

In order to find new molecules for antiviral drug design, we screened 102 ethyl acetate extracts from New-Caledonian flora for antiviral activity against the dengue 2 virus RNA-dependant RNA polymerase (DV-NS5 RdRp). The leaf extract of Dacrydium balansae, which strongly inhibited the DV-NS5, was submitted to bioguided fractionation. Four biflavonoids ( 1- 4), three sterols ( 5- 7), and two stilbene derivatives ( 8- 9) were identified and evaluated for their antiviral potential on the DV-NS5 RdRp. Biflavonoids appeared to be potent inhibitors of DV-NS5 RdRp with IC (50)s between 0.26 and 3.12 µM. Inhibitory activity evaluations against the RNA polymerase from other Flaviviridae viruses allowed us to conclude that these compounds are specific inhibitors of the DV RNA polymerase. The strongest inhibitions were observed with hinokiflavone ( 4), but podocarpusflavone A ( 2) is the strongest noncytotoxic inhibitor of the DV-NS5 and it also displayed polymerase inhibitory activity in a DV replicon. A preliminary structure-activity relationship study (SARs) revealed the necessity of the biflavonoid skeleton, the influence of number and position of methoxylations, and the importance of a free rotation of the linkage between the two apigenin monomers of the biflavonoids. To the best of our knowledge, podocarpusflavone A ( 2) is the strongest noncytotoxic non-nucleotide molecule exhibiting a specific inhibitory activity against the RNA polymerase domain of DV-NS5 and thus is promising for chemotherapy development against dengue fever.