Interaction of the disaccharide trehalose with a phospholipid bilayer: a molecular dynamics study

The disaccharide trehalose is well known for its bioprotective properties. Produced in large amounts during stress periods in the life of organisms able to survive potentially damaging conditions, trehalose plays its protective role by stabilizing biostructures such as proteins and lipid membranes. In this study, molecular dynamics simulations are used to investigate the interaction of trehalose with a phospholipid bilayer at atomistic resolution. Simulations of the bilayer in the absence and in the presence of trehalose at two different concentrations (1 or 2 molal) are carried out at 325 K and 475 K. The results show that trehalose is able to minimize the disruptive effect of the elevated temperature and stabilize the bilayer structure. At both temperature, trehalose is found to interact directly with the bilayer through hydrogen bonds. However, the water molecules at the bilayer surface are not completely replaced. At high temperature, the protective effect of trehalose is correlated with a significant increase in the number of trehalose-bilayer hydrogen bonds, predominantly through an increase in the number of trehalose molecules bridging three or more lipid molecules.     

Envelope ultrastructure of uncultured naturally occurring magnetotactic cocci

Magnetotactic bacteria are microorganisms that respond to magnetic fields. We studied the surface ultrastructure of uncultured magnetotactic cocci collected from a marine environment by transmission electron microscopy using freeze-fracture and freeze-etching. All bacteria revealed a Gram-negative cell wall. Many bacteria possessed extensive capsular material and a S-layer formed by particles arranged with hexagonal symmetry. No indication of a metal precipitation on the surface of these microorganisms was observed. Numerous membrane vesicles were observed on the surface of the bacteria. Flagella were organized in bundles originated in a depression on the surface of the cells. Occasionally, a close association of the flagella with the magnetosomes that remained attached to the replica was observed. Capsules and S-layers are common structures in magnetotactic cocci from natural sediments and may be involved in inhibition of metal precipitation on the cell surface or indirectly influence magnetotaxis.     

Studies on the production and regulation of interleukin,IL-13, IL-4 and interferon-gamma in human Schistosomiasis mansoni

The production and regulation of interleukin (IL) IL-13, IL-4 and interferon-gamma was evaluated in different clinical forms of human schistosomiasis. The mechanisms of immune regulation are apparently different in the various clinical stages of the disease, some of them being antigen specific.     

Structure and orientation of Apo B-100 peptides into a lipid bilayer

Peptides corresponding to lipid binding domains of Apo B-100 were synthesized, purified, and incubated with dimyristoylphosphatidylcholine (DMPC) liposomes. The secondary structure of the apo B-100 peptide-lipid complexes was evaluated by attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR). Those peptides belonging to the hydrophobic core domain of apo B-100 when associated with phospholipids were rich in sheet structure; a predominant helical conformation was shown to be associated with one peptide located in a surface region of apo B-100. IR dichroic spectra revealed, in the case of the core peptides, that the sheet component is the only oriented structure with respect to the phospholipid acyl chains. This orientation of the sheet was recently found in LDL particles after proteolytic digestion by trypsin (Goormaghtigh, E., Cabiaux, V., De Meutter, J., Rosseneu, M., and Ruysschaert, J. M., 1993,Biochemistry 32, 6104–6110). Altogether, the data suggest that sheet, present in a high proportion in the native apo B-100, is probably another protein structure in addition to the amphipathic helix which strongly interacts with the lipid outer layer surrounding the LDL particle.Abbreviations used Apo apolipoprotein - ATR attenuated total reflection - CD circular dichroism - DMPC dimyris-toylphosphatidylcholine - DMSO dimethylsulfoxide - FTIR Fourier transform infrared spectroscopy - HPLC high-performance liquid chromatography - LDL low density lipoprotein - TFA trifluoroacetic acid - C_x apoB-100 core peptide corresponding to the following residues: C₂, 2462–2482; C₃, 4208–4231; C₅, 4493–4513; and C₇, 4271–4288 - S₆ apoB-100 surface Peptide Corresponding to Residues 374–400     

The Tropical Biominer Project: mining old sources for new drugs

The Tropical Biominer Project is a recent initiative from the Federal University of Minas Gerais (UFMG) and the Oswaldo Cruz foundation, with the participation of the Biominas Foundation (Belo Horizonte, Minas Gerais, Brazil) and the start-up Homologix. The main objective of the project is to build a new resource for the chemogenomics research, on chemical compounds, with a strong emphasis on natural molecules. Adopted technologies include the search of information from structured, semi-structured, and non-structured documents (the last two from the web) and datamining tools in order to gather information from different sources. The database is the support for developing applications to find new potential treatments for parasitic infections by using virtual screening tools. We present here the midpoint of the project: the conception and implementation of the Tropical Biominer Database. This is a Federated Database designed to store data from different resources. Connected to the database, a web crawler is able to gather information from distinct, patented web sites and store them after automatic classification using datamining tools. Finally, we demonstrate the interest of the approach, by formulating new hypotheses on specific targets of a natural compound, violacein, using inferences from a Virtual Screening procedure.     

New molecular markers for phlebotomine sand flies

Using degenerate-primers PCR we isolated and sequenced fragments from the sand fly Lutzomyia longipalpis homologous to two behavioural genes in Drosophila, cacophony and period. In addition we identified a number of other gene fragments that show homology to genes previously cloned in Drosophila. A codon usage table for L. longipalpis based on these and other genes was calculated. These new molecular markers will be useful in population genetics and evolutionary studies in phlebotomine sand flies and in establishing a preliminary genetic map in these important leishmaniasis vectors.     

The human VPAC1 receptor: three-dimensional model and mutagenesis of the N-terminal domain

The human VPAC(1) receptor for vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase activating peptide belongs to the class II family of G-protein-coupled receptors with seven transmembrane segments. Like for all class II receptors, the extracellular N-terminal domain of the human VPAC(1) receptor plays a predominant role in peptide ligand recognition. To determine the three-dimensional structure of this N-terminal domain (residues 1-144), the Protein Data Bank (PDB) was screened for a homologous protein. A subdomain of yeast lipase B was found to have 27% sequence identity and 50% sequence homology with the N-terminal domain (8) of the VPAC(1) receptor together with a good alignment of the hydrophobic clusters. A model of the N-terminal domain of VPAC(1) receptor was thus constructed by homology. It indicated the presence of a putative signal sequence in the N-terminal extremity. Moreover, residues (Glu(36), Trp(67), Asp(68), Trp(73), and Gly(109)) which were shown to be crucial for VIP binding are gathered around a groove that is essentially negatively charged. New putatively important residues for VIP binding were suggested from the model analysis. Site-directed mutagenesis and stable transfection of mutants in CHO cells indicated that Pro(74), Pro(87), Phe(90), and Trp(110) are indeed important for VIP binding and activation of adenylyl cyclase activation. Combination of molecular modeling and directed mutagenesis provided the first partial three-dimensional structure of a VIP-binding domain, constituted of an electronegative groove with an outspanning tryptophan shell at one end, in the N-terminal extracellular region of the human VPAC(1) receptor.