Arie Schouten

Adhesion mechanism of human beta 2-glycoprotein I to phospholipids based on its crystal structure

Human β2‐glycoprotein I is a heavily glycosylated five‐domain plasma membrane‐adhesion protein, which has been implicated in blood coagulation and clearance of apoptotic bodies from the circulation. It is also the key antigen in the autoimmune disease anti‐phospholipid syndrome. The crystal structure of β2‐glycoprotein I isolated from human plasma reveals an elongated fish‐hook‐like arrangement of the globular short consensus repeat domains. Half of the C‐terminal fifth domain deviates strongly from the standard fold, as observed in domains one to four. This aberrant half forms a specific phospholipid‐binding site. A large patch of 14 positively charged residues provides electrostatic interactions with anionic phospholipid headgroups and an exposed membrane‐insertion loop yields specificity for lipid layers. The observed spatial arrangement of the five domains suggests a functional partitioning of protein adhesion and membrane adhesion over the N‐ and C‐terminal domains, respectively, separated by glycosylated bridging domains. Coordinates are in the Protein Data Bank (accession No. 1QUB).

Structure of a Drosophila sigma class glutathione S-transferase reveals a novel active site topography suited for lipid peroxidation products

Insect glutathione-S-transferases (GSTs) are grouped in three classes, I, II and recently III; class I (Delta class) enzymes together with class III members are implicated in conferring resistance to insecticides. Class II (Sigma class) GSTs, however, are poorly characterized and their exact biological function remains elusive. Drosophila glutathione S-transferase-2 (GST-2) (DmGSTS1-1) is a class II enzyme previously found associated specifically with the insect indirect flight muscle. It was recently shown that GST-2 exhibits considerable conjugation activity for 4-hydroxynonenal (4-HNE), a lipid peroxidation product, raising the possibility that it has a major anti-oxidant role in the flight muscle. Here, we report the crystal structure of GST-2 at 1.75A resolution. The GST-2 dimer shows the canonical GST fold with glutathione (GSH) ordered in only one of the two binding sites. While the GSH-binding mode is similar to other GST structures, a distinct orientation of helix alpha6 creates a novel electrophilic substrate-binding site (H-site) topography, largely flat and without a prominent hydrophobic-binding pocket, which characterizes the H-sites of other GSTs. The H-site displays directionality in the distribution of charged/polar and hydrophobic residues creating a binding surface that explains the selectivity for amphipolar peroxidation products, with the polar-binding region formed by residues Y208, Y153 and R145 and the hydrophobic-binding region by residues V57, A59, Y211 and the C-terminal V249. A structure-based model of 4-HNE binding is presented. The model suggest that residues Y208, R145 and possibly Y153 may be key residues involved in catalysis.

Factor B structure provides insights into activation of the central protease of the complement system

Factor B is the central protease of the complement system of immune defense. Here, we present the crystal structure of human factor B at 2.3-Å resolution, which reveals how the five-domain proenzyme is kept securely inactive. The canonical activation helix of the Von Willebrand factor A (VWA) domain is displaced by a helix from the preceding domain linker. The two helices conformationally link the scissile-activation peptide and the metal ion–dependent adhesion site required for binding of the ligand C3b. The data suggest that C3b binding displaces the three N-terminal control domains and reshuffles the two central helices. Reshuffling of the helices releases the scissile bond for final proteolytic activation and generates a new interface between the VWA domain and the serine protease domain. This allosteric mechanism is crucial for tight regulation of the complement-amplification step in the immune response.

Structure of apo‐phosphatidylinositol transfer protein α provides insight into membrane association

Phosphatidylinositol transfer protein α (PITPα) is a ubiquitous and highly conserved protein in multicellular eukaryotes that catalyzes the exchange of phospholipids between membranes in vitro and participates in cellular phospholipid metabolism, signal transduction and vesicular trafficking in vivo. Here we report the three‐dimensional crystal structure of a phospholipid‐free mouse PITPα at 2.0 Å resolution. The structure reveals an open conformation characterized by a channel running through the protein. The channel is created by opening the phospholipid‐binding cavity on one side by displacement of the C‐terminal region and a hydrophobic lipid exchange loop, and on the other side by flattening of the central β‐sheet. The relaxed conformation is stabilized at the proposed membrane association site by hydrophobic interactions with a crystallographically related molecule, creating an intimate dimer. The observed open conformer is consistent with a membrane‐bound state of PITP and suggests a mechanism for membrane anchoring and the presentation of phosphatidylinositol to kinases and phospholipases after its extraction from the membrane. Coordinates have been deposited in the Protein Data Bank (accession No. 1KCM).

Attention deficits are not characteristic of schoolchildren with newly diagnosed idiopathic or cryptogenic epilepsy.

 Purpose: To compare problems of attention in schoolchildren with newly diagnosed idiopathic or cryptogenic epilepsy with those in healthy classmates.

Learning and memory of school children with epilepsy: a prospective controlled longitudinal study

The aim of the study was to determine whether learning and memory are compromised in school children with recently diagnosed idiopathic and/or cryptogenic epilepsy and to study relationships between learning and memory and psychosocial and epilepsy variables. Word span and learning of locations were assessed within 48 hours after diagnosis of epilepsy and three and 12 months later, in 69 school children with epilepsy (aged 9.1 years, SD 2.7; 33 males, 36 females) and 66 classmates. Results showed that patients and controls performed similarly in registration, recall, and retention. Patients recalled slightly less than controls when probed under conditions of increased demand on working memory. Maladaptive reactions of parents and children to the onset of epilepsy and not reaching 6-months of seizure remission contributed to poor performance. Individually, those patients who required special assistance at school, under-performed occasionally in one or the other component of memory. Although the proportion of under-performers was stable over time, the children composing the group did change. It was concluded that school children with new onset idiopathic or cryptogenic epilepsy are inordinately vulnerable when processing memory tasks. The vulnerability is neither persistent nor memory-specific.

Parents' Perceptions of Adversity Introduced by Upheaval and Uncertainty at the Onset of Childhood Epilepsy

Summary:  Purpose: We report the parents perceptions of and reactions to the onset of “epilepsy only” and the implications for continuity of parenting.

Conformational polymorphism of d-sorbitol (d-glucitol): the crystal and molecular structures of d-glucitol 2/3-hydrate and epsilon d-glucitol

Abstract The crystal structures of d -glucitol 2/3-hydrate (1) and epsilon d -glucitol (2) were determined by X-ray crystallography and refined to final conventional parameters of R=0.034 and 0.050, respectively. The conformations of the three independent molecules of 1 and one of the two independent molecules of 2 are similar and exhibit, bent-chain, sickle conformations of the carbon chain, thus avoiding the unfavourable 1,3-parallel O//O interactions. However, the orientation of a terminal hydroxyl group differs from the one observed in the bent-chain conformation of the known A form. An even more striking observation is the unexpected, extended, zigzag conformation of the second independent molecule of 2, which results in a 1,3-parallel interaction between O-2 and O-4. Thus in the class of alditols, the crystals of the epsilon and A forms of d -glucitol constitute the rarely occurring type of conformational polymorphism.

Negative emotions in children with newly diagnosed epilepsy.

Summary: Purpose: To understand the emotional predicament in children with recently diagnosed idiopathic or cryptogenic epilepsy.

Reaction of N-trityl amino acids with BOP: Efficient synthesis of t-butyl esters as well as N-trityl serine- and threonine-β-lactones

Upon exposure to methoxymethylamine and BOP, the stable hydroxybenzotriazolyl amide of TrPheOH was isolated instead of the expected Weinreb amide. This amide behaves as an active amide similar to the Weinreb amide and could be used, among others, for the synthesis of t-Bu esters. Reaction of N-trityl serine and threonine led to the corresponding β-lactones in unprecedented high yields.