Torgils Fossen

The nuclear lamina lines the inner nuclear membrane providing a structural framework for the nucleus. Cellular processes, such as nuclear envelope breakdown during mitosis or nuclear export of large ribonucleoprotein complexes, are functionally linked to the disassembly of the nuclear lamina. In general, lamina disassembly is mediated by phosphorylation, but the precise molecular mechanism is still not completely understood. Recently, we suggested a novel mechanism for lamina disassembly during the nuclear egress of herpesviral capsids which involves the cellular isomerase Pin1. In this study, we focused on mechanistic details of herpesviral nuclear replication to demonstrate the general importance of Pin1 for lamina disassembly. In particular, Ser22-specific lamin phosphorylation consistently generates a Pin1-binding motif in cells infected with human and animal alpha-, beta-, and gammaherpesviruses. Using nuclear magnetic resonance spectroscopy, we showed that binding of Pin1 to a synthetic lamin peptide induces its cis/trans isomerization in vitro. A detailed bioinformatic evaluation strongly suggests that this structural conversion induces large-scale secondary structural changes in the lamin N-terminus. Thus, we concluded that a Pin1-induced conformational change of lamins may represent the molecular trigger responsible for lamina disassembly. Consistent with this concept, pharmacological inhibition of Pin1 activity blocked lamina disassembly in herpesvirus-infected fibroblasts and consequently impaired virus replication. In addition, a phospho-mimetic Ser22Glu lamin mutant was still able to form a regular lamina structure and overexpression of a Ser22-phosphorylating kinase did not induce lamina disassembly in Pin1 knockout cells. Intriguingly, this was observed in absence of herpesvirus infection proposing a broader importance of Pin1 for lamina constitution. Thus, our results suggest a functional model of similar events leading to disassembly of the nuclear lamina in response to herpesviral or inherent cellular stimuli. In essence, Pin1 represents a regulatory effector of lamina disassembly that promotes the nuclear pore-independent egress of herpesviral capsids.

Structure-activity relationship studies of the cyclopentapeptide CXCR4 antagonists (cyclo(-l-/d-Arg(1)-Arg(2)-2-Nal(3)-Gly(4)-d-Tyr(5)-)) suggest that the l-/d-Arg(1)-Arg(2)-2-Nal(3) tripeptide sequence contained within these cyclopentapeptides serves as a recognition motif for peptidic CXCR4 antagonists. Starting by dissecting the cyclopentapeptide structure and reintroducing cyclic constraints in a stepwise manner, we here report a novel class of scaffold-based tripeptidomimetic CXCR4 antagonists based on the d-Arg-Arg-2-Nal motif. Biological testing of the prototype compounds showed that they represent new peptidomimetic hits; importantly, the modular nature of the scaffold provides an interesting starting point for future ligand optimization.

The anthocyanin–flavone C-glycoside, (malvidin 3-O-(6II-O-α-rhamnopyranosylAIV-β-glucopyranosideAII)-5-O-β-glucopyranosideAIII) (apigenin 6-C-(2II-O-β-glucopyranosylFIII-β-glucopyranosideFII)) malonateAV (AIV-4→AV-1, FIII-6→AV-3) (1), has been isolated from leaves of Oxalis triangularis A. St.-Hil. In the 1D 1H NMR spectrum of 1 dissolved in CD3OD–CF3CO2D (95:5), MTFA, recorded 45min after sample preparation, this covalently linked dimer occurred mainly as flavylium cation (38%) and two equilibrium forms assigned to be quinonoidal bases (54%), whereas

The novel anthocyanins, malvidin 3-O-(6-O-(4-O-malonyl-α-rhamnopyranosyl)-β-glucopyranoside)-5-O-β-glucopyranoside (2), malvidin 3-O-(6-O-α-rhamnopyranosyl-β-glucopyranoside)-5-O-(6-O-malonyl-β-glucopyranoside) (3), malvidin 3-O-(6-O-(4-O-malonyl-α-rhamnopyranosyl)-β-glucopyranoside)-5-O-(6-O-malonyl-β-glucopyranoside) (4), malvidin 3-O-(6-O-(4-O-malonyl-α-rhamnopyranosyl)-β-glucopyranoside) (5) and malvidin 3-O-(6-O-(Z)-p-coumaroyl-β-glucopyranoside)-5-O-β-glucopyranoside (6), in addition to the 3-O-(6-O-α-rhamnopyranosyl-β-glucopyranoside)-5-O-β-glucopyranoside (1) and the 3-O-(6-O-(E)-p-coumaroyl-β-glucopyranoside)-5-O-β-glucopyranoside (7) of malvidin have been isolated from purple leaves of Oxalis triangularis A. St.-Hil. In pigments 2, 4 and 5 a malonyl unit is linked to the rhamnose 4-position, which has not been reported previously for any anthocyanin before. The identifications were mainly based on 2D NMR spectroscopy and electrospray MS.Five novel anthocyanins, the 3-(6-(4-malonylrhamnosyl)glucoside)-5-glucoside (2), the 3-(6-rhamnosylglucoside)-5-(6-malonylglucoside) (3), the 3-(6-(4-malonylrhamnosyl)glucoside)-5-(6-malonylglucoside) (4), the 3-(6-(4-malonylrhamnosyl)glucoside) (5) and the 3-(6-(Z)-pcoumaroylglucoside)-5-glucoside (6) of malvidin have been isolated from methanolic extracts of leaves of Oxalis triangularis.

Fenugreek (Trigonella foenum-graecum L.) is particularly used in Asia, Africa, and Mediterranean countries for its nutritional and medicinal value. The flavone C-glycosides, apigenin 6-C-beta-chinovopyranosyl-8-C-beta-galactopyranoside (6) and apigenin 6-C-beta-xylopyranosyl-8-C-(6'''-O-(3-hydroxy-3-methylglutaroyl)-beta-glucopyranoside) (7), in addition to the known flavone C-glycosides, apigenin 6,8-C-di-beta-galactopyranoside (1), apigenin 6-C-beta-xylopyranosyl-8-C-beta-galactopyranoside (2), apigenin 6-C-beta-arabinopyranosyl-8-C-beta-galactopyranoside (3), luteolin 8-C-beta-glucopyranoside (4), luteolin 6-C-beta-glucopyranoside (5), apigenin 8-C-beta-glucopyranoside (8), apigenin 6-C-beta-glucopyranoside (9), luteolin 8-C-(2''-O-(E)-p-coumaroyl-beta-glucopyranoside) (10), and apigenin 8-C-(2''-O-(E)-p-coumaroyl-beta-glucopyranoside) (11) were isolated from fenugreek seeds. Compounds 1, 5, and 10 were reported for the first time in this species. Signal duplication in the NMR spectra, with exception of spectra of the mono-6-C-substituted compounds, revealed the presence of rotameric conformers, created by rotational hindrance at the C (sp(3))-C (sp(2)) glycosyl-flavone linkage in these flavone C-glycosides.

The flavone C-glycosides luteolin 6-C-(2''-O-beta-xylopyranosyl-beta-glucopyranoside) (1), apigenin 6-C-(2''-O-alpha-rhamnopyranosyl-beta-glucopyranoside) (2), apigenin 6-C-(2''-O-beta-xylopyranosyl-beta-glucopyranoside) (3), apigenin 6-C-(2''-O-(6'''-(E)-caffeoylglucoside)-beta-glucopyranoside) (4), and apigenin 6-C-(2''-O-(6'''-(E)-p-coumaroylglucoside)-beta-glucopyranoside) (5) have been isolated from the purple leaves of Oxalis triangularis. Compound 4 is new, while 5 has previously been isolated from Cucumis sativus after treatment with silicon and infection with Sphaerotheca fuliginea. Signal duplication in the NMR spectra of 2, 4, and 5 revealed the presence of rotameric conformers, created by rotational hindrance at the C(sp3) -C(sp2) glucosyl-flavone linkage in these flavone C-glycosides.

Seven C-glycosyl-3-deoxyanthocyanidins were made from their corresponding C-glycosylflavones. The structures of their rearrangement products, which were formed in acidic aqueous solutions, were elucidated. Rotameric conformers were detected for all of the 8-C-glycosyldeoxyanthocyanidins but were absent for their isomeric 6-C-analogues in acidified methanolic NMR solvent. A correlation method based on HPLC-DAD and NMR integration of similar samples made it possible for the first time to determine accurately the proportions of two isomeric 6-C- and 8-C-glycosylflavonoids occurring in mixtures. Each of the C-glycosyldeoxyanthocyanidins established fixed equilibrium proportions with their corresponding A-ring isomer in aqueous solutions, even under relatively strong acidic conditions (pH approximately 1), whether one started with pure 6-C- or 8-C-glycosyl-3-deoxyanthocyanidin. The nature of the aglycone, C-glycosyl moiety, and temperature were found to affect the equilibrium proportions. Increased water content (to a certain level) and temperatures were shown to increase the isomerization rates. The flavylium cations were the only equilibrium forms present at detectable quantities. The significance of rotation of the A-ring during isomerization was confirmed by lack of rearrangement of both 6-C- and 8-C-glycosyl-3-deoxy-5-carboxypyranoanthocyanidins. The intermediary C-ring open forms of the C-glycosyldeoxyanthocyanidins experience fast ring closure to their cyclic forms, which may reduce irreversible degradation reported for open chalcone forms of the common anthocyanins. The stable C-glycosyl-3-deoxyanthocyanidins may thus attract interest as possible colorants in the food industry, etc.

The human immunodeficiency virus type 1 (HIV-1) p6 protein has recently been recognized as a docking site for several cellular and viral binding partners and is important for the formation of infectious viruses. Most of its known functions are suggested to occur under hydrophobic conditions near the cytoplasmic membrane, where the protein is presumed to exist in its most structured state. Although p6 is involved in manifold specific interactions, the protein has previously been considered to possess a random structure in aqueous solution. We show that p6 exhibits a defined structure with N- and C-terminal helical domains, connected by a flexible hinge region in 100mM dodecylphosphocholine micelle solution at pH 7 devoid of any organic co-solvents, indicating that this is a genuine limiting structural feature of the molecule in a hydrophobic environment. Furthermore, we show that p6 directly interacts with a cytoplasmic model membrane through both N-terminal and C-terminal regions by use of surface plasmon resonance (SPR) spectroscopy. Phosphorylation of Ser-40 located in the center of the C-terminal α-helix does not alter the secondary structure of the protein but amplifies the interaction with membranes significantly, indicating that p6 binds to the polar head groups at the surface of the cytoplasmic membrane. The increased hydrophobic membrane interaction of p6(23-52) S40F correlated with the observed increased amount of the polyprotein Gag in the RIPA insoluble fraction when Ser40 of p6 was mutated with Phe indicating that p6 modulates the membrane interactions of HIV-1 Gag.