No abstract

Molecular modelling techniques have been applied to compute the conformations accessible to bacterial deep rough lipopolysaccharide of Escherichia coli (Re-LPS). Analyses of the results showed that the models typically exhibit a tilt of the diglucosamine backbone with respect to the membrane normal of 53 7" while both the glucosamine ring planes are orientated approximately parallel to the membrane normal. Different models were found to show compact and elongated types of acyl chain arrangements, both producing anisotropic lateral dimensions of the models of 1.0-1.1 nm and 1.7-2.0 nm for the shorter and the longer side, respectively. The conformationally allowed range of the isolated dOclA(a-2-4)dOclA disaccharide (dOclA = 3-deoxy-~-mannooctulosonic acid) was found to be extremely limited. It appeared that the dOclA disaccharide (dOclA)2 is centred at the top of the Re-LPS molecule preferring two orientations stabilized by hydrogen bonds involving only one phosphate group of the lipid A moiety at a time.The effect of charges on the Re-LPS conformations has been studied in separate calculations. From these calculations it was obvious that charges have no significant effects on the conformations of the isolated lipid A and (dOclA)2 moieties. However, it was found that the orientation of (dOclA), with respect to the lipid A part is highly sensitive to charges, i. e. in the charged models the proximity of phosphate and carboxyl groups is prevented by strong electrostatic repulsion between these negatively charged groups.In order to rationalize the acyl chain packing of the models, a simple geometrical model which correlates the tilt of the diglucosamine backbone with the energetically favoured close packing of the acyl chains is proposed. Furthermore, the possibility of a chelate-like complexation of divalent cations and its contribution to head group mobility is discussed.Lipopolysaccharides (LPS) are the main constituent of the outer leaflet of the outer membrane of Gram-negative bacteria. As LPS are of special significance to bacterial viability and to interactions of bacteria with host organisms, many studies have been focused on the elucidation of their structure and function [l -51. Chemically, LPS consists of a lipid A and a polysaccharide component, of which the latter is usually subdivided into two regions [6], i.e. the 0-specific chain and the core oligosaccharide. Re-LPS is the smallest LPS found in viable Escherichia coli bacteria [2, 71. It consists of the lipid A part and a partial core built up by a dimer of the rare saccharide 3-deoxy-~-manno-octu~osonic acid (dOclA). Recent work has shown that LPS endotoxic activity is determined by structural components as they are present in E. coli lipid A, i.e. a 8-1-6 interlinked diglucosamine, two phosphoryl groups and at least five, but not more than six, fatty acids including one or two 3-acyloxyacyl groups [S]. However, as itCorrespondence to

Investigations o f multibilayered films b y X-ray diffraction have successfully been applied t o biological material and contributed a lot o f structural information about biological membranes. Analysis of t h e intensity d a t a obtained from a simple p o w d e r diffraction experiment yield t h e one-dimensional electron-density distribution normal t o the membrane plane. It is however

ZusammenfassungDie enge Zusammenarbeit der vier Berliner Universitätsbibliotheken Freie Universität Berlin (FU), Humboldt-Universität zu Berlin (HU), Technische Universität Berlin (TU), Universität der Künste Berlin (UdK). reicht weit zurück. Bereits vor der Jahrtausendwende haben die Berliner Universitätsbibliotheken (UBs) gemeinsam das Bibliothekssystem Aleph 500 ausgewählt und implementiert, danach folgten weitere Systeme – das Linking System SFX, die Digitale Bibliothek MetaLib und das Bibliotheksportal Primo. Es war daher folgerichtig und selbstverständlich, dass auch die Auswahl und Implementierung eines neuen Bibliothekssystems in enger Abstimmung und Zusammenarbeit erfolgte. Die Erfahrungen bei Vertragsverhandlungen und Implementierung von Alma sind Gegenstand des folgenden Berichtes.