Kees Versluis

Homodimeric galectin-7 (p53-induced gene 1) is a negative growth regulator for human neuroblastoma cells

The extracellular functions of galectin-7 (p53-induced gene 1) are largely unknown. On the surface of neuroblastoma cells (SK-N-MC), the increased GM1 density, a result of upregulated ganglioside sialidase activity, is a key factor for the switch from proliferation to differentiation. We show by solid-phase and cell assays that the sugar chain of this ganglioside is a ligand for galectin-7. In serum-supplemented proliferation assays, galectin-7 reduced neuroblastoma cell growth without the appearance of features characteristic for classical apoptosis. The presence of galectin-3 blocked this effect, which mechanistically resembles that of galectin-1. By virtue of carbohydrate binding, galectin-7 thus exerts neuroblastoma growth control similar to galectin-1 despite their structural differences. In addition to p53-linked proapoptotic activity intracellularly, galectin-7, acting as a lectin on the cell surface, appears to be capable of reducing cancer cell proliferation in susceptible systems.

Endogenous phosphatidylcholine and a long spacer ligand stabilize the lipid-binding groove of CD1b.

CD1 proteins present lipid antigens to T cells. The antigens are acquired in the endosomal compartments. This raises the question of how the large hydrophobic CD1 pockets are preserved between the moment of biosynthesis in the endoplasmic reticulum and arrival to the endosomes. To address this issue, the natural ligands associated with a soluble form of human CD1b have been investigated. Using isoelectric focusing, native mass spectrometry and resolving the crystal structure at 1.8 Å resolution, we found that human CD1b is simultaneously associated with endogenous phosphatidylcholine (PC) and a 41–44 carbon atoms‐long spacer molecule. The two lipids appear to work in concert to stabilize the CD1b groove, their combined size slightly exceeding the maximal groove capacity. We propose that the spacer serves to prevent binding of ligands with long lipid tails, whereas short‐chain lipids might still displace the PC, which is exposed at the groove entrance. The data presented herein explain how the CD1b groove is preserved, and provide a rationale for the in vivo antigen‐binding properties of CD1b.

Free and cell wall-bound phenolics and other constituents from healthy and fungus-infected carnation (Dianthus caryophyllus L.) stems

Phenolic compounds and related substances from carnation stems infected with Fusarium oxysporum f.sp. dianthi were investigated. Healthy stems contained, esterified to wall polysaccharides, among others benzoic, p-hydroxybenzoic, vanillic, trans p-coumaric, cis and trans ferulic, 3-methoxy-4-hydroxy-n-chlorophenyl propionic and (in large amounts) dihydroferulic acid. Fungal infection affected the concentrations of these phenolic acids and induced the accumulation of two types of anthranilic acid derivatives. One group of those compounds included the dianthramides which were further characterized by HPLC-MS. A representative of the other group was identified as 2,2′-dicarboxy-5,5′-dihydroxy-N,N-diphenylamine, a new natural product.

Metal binding of Lissoclinum patella metabolites. Part 1: Patellamides A, C and ulithiacyclamide A

Abstract Studies on three Thz, and Oxn containing cyclic peptides, patellamide A and C (1, 3) and ulithiacyclamide A (9) isolated from the Indo-Pacific ascidian (seasquirt) Lissoclinum patella have delineated their metal binding selectivity. Patellamide C (3) shows extreme selectivity for Cu2+ even in the presence of an excess of Zn2+ and shows no binding at all to Co2+, Ni2+ and Hg2+. Patellamide A (1) is less selective for Cu2+, whereas ulithiacyclamide A (9) shows selectivity similar to that of patellamide C (3). The selectivity was studied by circular dichroism spectroscopy and mass spectrometry. The CD spectra obtained whilst patellamide C was slowly titrated with Cu2+ show one isosbestic point indicating the Cu2+ binding involves only two conformations. These studies indicate that Cu2+, not Zn2+ is the biologically relevant metal for these compounds and point towards a potential ecological function of these complexes.

Structure Determination and MSn Analysis of Two New Lissoclinamides Isolated from the Indo–Pacific Ascidian Lissoclinum patella: NOE Restrained Molecular Dynamics Confirms the Absolute Stereochemistry Derived by Degradative Methods

Abstract Two new lissoclinamides, lissoclinamides 9 and 10 were isolated from an Indonesian collection of the ascidian Lissoclinum patella along with the known patellamide C. The structures of the lissoclinamides were determined by a combination of 2D NMR, selective 1D TOCSY, MS and MSn techniques. The assignment of absolute stereochemistry was achieved by the hydrolysis of lissoclinamides 9 and 10 followed by chiral TLC. In the case of lissoclinamide 9, NOE restrained molecular dynamics studies were also performed confirming the proposed stereochemistry.

Metal binding of Lissoclinum patella metabolites. Part 2: Lissoclinamides 9 and 10

Abstract Studies on the Thz, Thn and Oxn containing cyclic peptides, lissoclinamides 9 ( 9 ) and 10 ( 10 ) isolated from the Indo-Pacific ascidian (seasquirt) Lissoclinum patella have delineated their metal binding selectivity. MS and CD competition studies show that lissoclinamide 10 ( 10 ) shows selectivity for Cu 2+ in the presence of an excess of Zn 2+ whereas lissoclinamide 9 ( 9 ) is less selective for Cu 2+ . Comparison of the solution state conformations derived from nOe restrained molecular dynamics and additional Monte–Carlo conformational searches suggested binding environments for the Cu 2+ which confirmed the MS measurements and suggested a reason for the selectivity in the case of lissoclinamides 9 and 10.

Non-covalent synthesis of calix[4]arene-capped porphyrins in polar solvents via ionic interactions

Non-covalent synthesis of calix[4]arene capped porphyrins can be achieved in polar solvents (up to 45% molar fraction of water) via ionic interaction. Thus tetracationic meso-tetrakis(N-alkylpyridinium-3-yl) porphyrins 1a–d and tetra anionic 25,26,27,28-tetrakis(2-ethoxyethoxy)-calix[4]arene tetrasulfonate 2 self-assemble in an entropy driven process in 1:1 stoichiometry with association constants K1·2 as high as 107 M−1 in methanol. The thermodynamic stability remains high even in the presence of competing salts: 10−2 M Bu4NClO4 (4500 times the concentration of the building blocks) gives a reduction in K1·2 of only 10 times. Ternary complexes 1a·2·L using 1-methylimidazole or pyridine as axial ligands (L) have been obtained with L residing outside the assembly cavity.

The detection of intermediates in the ruthenium(II) catalysed asymmetric hydrogenation of ketones using electrospray ionisation mass spectrometry

The use of electrospray ionisation mass spectrometry for the detection of the intermediate species involved in the ruthenium(II)/amino alcohol reduction of ketones to alcohols is described.

Formation of octadecadienoate dimers by soybean lipoxygenases

The aim of this investigation was to determine whether the regioselectivity found for lipoxygenases in the formation of fatty acid hydroperoxides from linoleic acid is reflected in the formation of dimeric products in secondary reactions involving linoleic acid, product hydroperoxide and lipoxygenase. A method was therefore developed for the separation and identification of dimers formed by fusion of two linoleic acid radicals or a linoleic acid radical and linoleate. The method includes solid-phase extraction, preparative separation of products by thin-layer chromatography, derivatization to the corresponding fully hydrogenated methyl esters and capillary gas chromatography (GC) coupled with electron impact mass spectrometry. We present evidence that the formation of octadecadienoate dimers, during the secondary reaction of soybean lipoxygenase-1 or lipoxygenase-3, is a nonenzymic process that can be envisaged by nonspecific association of intermediate fatty acid radicals (L*) that have dissociated from the enzyme. We could show that the relative amounts of different octadecadienoate dimers formed remain unaltered, regard-less of pH and type of soybean isoenzyme used. Quantitative analysis by GC showed that under the reaction conditions used, the formation of dimers branching at the 13-position is preferred.

Copper and iron interactions with angiotensin-converting enzyme inhibitors. A study by fast-atom bombardment tandem mass spectrometry

Fast atom bombardment, combined with high-energy collision-induced tandem mass spectrometry, has been used to investigate gas-phase metal-ion interactions with captopril, enalaprilat and lisinopril, all angiotensin-converting enzyme inhibitors.Suggestions for the location of metal-binding sites are presented. For captopril, metal binding occurs most likely at both the sulphur and the nitrogen atom. For enalaprilat and lisinopril, binding preferably occurs at the amine nitrogen. Copyright 1999 John Wiley & Sons, Ltd.