Continuum electrostatic model for the binding of cytochrome c2 to the photosynthetic reaction center from Rhodobacter sphaeroides

Electrostatic interactions are important for protein-protein association. In this study, we examined the electrostatic interactions between two proteins, cytochrome c(2) (cyt c(2)) and the reaction center (RC) from the photosynthetic bacterium Rhodobacter sphaeroides, that function in intermolecular electron transfer in photosynthesis. Electrostatic contributions to the binding energy for the cyt c(2)-RC complex were calculated using continuum electrostatic methods based on the recent cocrystal structure [Axelrod, H. L., et al. (2002) J. Mol. Biol. 319, 501-515]. Calculated changes in binding energy due to mutations of charged interface residues agreed with experimental results for a protein dielectric constant epsilon(in) of 10. However, the electrostatic contribution to the binding energy for the complex was close to zero due to unfavorable desolvation energies that compensate for the favorable Coulomb attraction. The electrostatic energy calculated as a function of displacement of the cyt c(2) from the bound position showed a shallow minimum at a position near but displaced from the cocrystal configuration. These results show that although electrostatic steering is present, other short-range interactions must be present to contribute to the binding energy and to determine the structure of the complex. Calculations made to model the experimental data on association rates indicate a solvent-separated transition state for binding in which the cyt c(2) is displaced approximately 8 A above its position in the bound complex. These results are consistent with a two-step model for protein association: electrostatic docking of the cyt c(2) followed by desolvation to form short-range van der Waals contacts for rapid electron transfer.     

Solvent deuterium isotope effect on the oxidation of o-diphenols by tyrosinase

A solvent deuterium isotope effect on the catalytic affinity (K(m)) and rate constant (k(cat)) of tyrosinase in its action on 4-tert-butylcatechol (TBC) was observed. Both parameters decreased as the molar fraction of deuterated water in the medium increased, while the k(cat)/K(m) ratio remained constant. In a proton inventory study, the representation of k(cat)(f(n))/k(cat)(f(0)) and K(m)(f(n))/K(m)(f(0)) vs. n (atom fractions of deuterium) was linear, indicating that, of the four protons transferred from the two molecules of substrate and which are oxidized in one turnover, only one is responsible for the isotope effects. The fractionation factor of 0.64+/-0.02 contributed to identifying the possible proton acceptor. Possible mechanistic implications are discussed.     

Delivery to macrophages and toxic action of etoposide carried in mouse red blood cells

Erythrocytes could be used as physiological carriers of active compounds. Several substances can be loaded into erythrocytes by hypotonic dialysis methods. Furthermore, carrier erythrocyte membrane can be chemically modified in order to promote increased arrival of the loaded compound to macrophages. In this work, we have prepared erythrocytes loaded with etoposide. We found conditions to obtain high etoposide encapsulation yields with minor alteration of some cell parameters of these carrier erythrocytes. Etoposide loaded into erythrocytes is mainly localised in the cytoplasmic compartment. Membrane modification of etoposide-loaded erythrocytes with band 3 crosslinkers produces an increased incorporation of the drug into macrophages mainly by phagocytosis process. The toxic effect of etoposide conveyed in these carrier erythrocytes determined as DNA fragmentation in macrophages was higher than that shown by free etoposide added at the same concentration in the culture medium to macrophages. These results seem to indicate the usefulness of this model to deliver this anti-tumour compound to macrophages, which might be useful in therapy.     

Molecular mechanism of membrane permeabilization by the peptide antibiotic surfactin

Surfactin, an acidic lipopeptide produced by various strains of Bacillus subtilis, behaves as a very powerful biosurfactant and possesses several other interesting biological activities. This work deals with the molecular mechanism of membrane permeabilization by incorporation of surfactin. The surfactin-induced vesicle contents leakage was monitored by following release of carboxyfluorescein entrapped into unilamellar vesicles made of palmitoyloleoylphosphatidylcholine (POPC). The effect of the addition of cholesterol, dipalmitoylphosphatidylcholine (DPPC) and palmitoyloleoylphosphatidylethanolamine (POPE) was also checked. It was observed that surfactin was able to induce content leakage at concentrations far below the onset surfactin/lipid ratio for membrane solubilization to occur, which in our system was around 0.92. Electron microscopy showed that vesicles were present after addition of surfactin at a ratio below this value, whereas no vesicles could be observed at ratios above it. Cholesterol and POPE attenuated the membrane-perturbing effect of surfactin, whereas the effect of DPPC was to promote surfactin-induced leakage, indicating that bilayer sensitivity to surfactin increases with the lipid tendency to form lamellar phases, which is in agreement with our previous observation that surfactin destabilizes the inverted-hexagonal structure. Fourier-transform infrared spectroscopy (FTIR) was used to specifically follow the effect of surfactin on different parts of the phospholipid bilayer. The effect on the C=O stretching mode of vibration of POPC indicated a strong dehydration induced by surfactin. On the other hand, the C-H stretching bands showed that the lipopeptide interacts with the phospholipid acyl chains, resulting in considerable membrane fluidization. The reported effects could be useful to explain surfactin-induced 'pore' formation underlying the antibiotic and other important biological actions of this bacterial lipopeptide.     

Extramedullary plasmacytoma presenting as a primary mass in the breast. A case report

BACKGROUND: Extramedullary plasmacytoma (EMP) of the breast is extremely rare, especially that not associated with multiple myeloma. CASE: A case of plasmacytoma of the breast in a 73-year-old man was diagnosed by fine needle aspiration cytology (FNAC). Aspiration smears revealed a dispersed population of plasmacytoid cells at various stages of maturation. The tumor was excised, and the histologic sections confirmed the cytologic diagnosis. CONCLUSION: FNAC diagnosis of plasmacytoma of the breast offers the opportunity to distinguish these neoplasms from primary mammary tumors and avoid unnecessary surgery.     

Identification of a novel Bardet-Biedl syndrome protein,BBS7, that shares structural features with BBS1 and BBS2

Bardet-Biedl syndrome (BBS) is a genetically heterogeneous disorder, the primary features of which include obesity, retinal dystrophy, polydactyly, hypogenitalism, learning difficulties, and renal malformations. Conventional linkage and positional cloning have led to the mapping of six BBS loci in the human genome, four of which (BBS1, BBS2, BBS4, and BBS6) have been cloned. Despite these advances, the protein sequences of the known BBS genes have provided little or no insight into their function. To delineate functionally important regions in BBS2, we performed phylogenetic and genomic studies in which we used the human and zebrafish BBS2 peptide sequences to search dbEST and the translation of the draft human genome. We identified two novel genes that we initially named "BBS2L1" and "BBS2L2" and that exhibit modest similarity with two discrete, overlapping regions of BBS2. In the present study, we demonstrate that BBS2L1 mutations cause BBS, thereby defining a novel locus for this syndrome, BBS7, whereas BBS2L2 has been shown independently to be BBS1. The motif-based identification of a novel BBS locus has enabled us to define a potential functional domain that is present in three of the five known BBS proteins and, therefore, is likely to be important in the pathogenesis of this complex syndrome.     

Hepatitis B surface antigen immunopurification using a plant-derived specific antibody produced in large scale

This paper provides an evaluation of a plant-derived HBsAg-specific antibody in the immunopurification of the recombinant HBsAg for vaccine purposes. This plant-derived antibody was obtained from different batches of 100-200kg of tobacco leaves and coupled to Sepharose CL-4B with high efficiency. The plant-derived antibody immunoaffinity matrix purification behavior (elution capacity, antigen purity, purification cycles, and ligand leakage) was comparable to that of its mouse-derived monoclonal antibody homolog. This result supports the feasibility of using this plant-derived antibody for the immunopurification of the Hepatitis B surface antigen for human use, opening a new possibility to overcome the constrain of monoclonal antibody production in mice.     

Involvement of p53 in alpha4beta1 integrin-mediated resistance of B-CLL cells to fludarabine

We recently showed that alpha4beta1 integrin induces B-cell chronic lymphocytic leukemia (B-CLL) cell resistance to fludarabine-induced apoptosis via upregulation of Bcl-xL. We have now studied whether p53 was involved in this response. Cells from five B-CLL patients with wild-type p53 determined by DNA sequencing, or from the EHEB cell line, cultured on the alpha4beta1 ligand H/89 during fludarabine treatment, showed significantly higher viability (P相似文献   

Structural and biochemical characterization of toad liver fatty acid-binding protein

Two paralogous groups of fatty acid-binding proteins (FABPs) have been described in vertebrate liver: liver FABP (L-FABP) type, extensively characterized in mammals, and liver basic FABP (Lb-FABP) found in fish, amphibians, reptiles, and birds. We describe here the toad Lb-FABP complete amino acid sequence, its X-ray structure to 2.5 A resolution, ligand-binding properties, and mechanism of fatty acid transfer to phospholipid membranes. Alignment of the amino acid sequence of toad Lb-FABP with known L-FABPs and Lb-FABPs shows that it is more closely related to the other Lb-FABPs. Toad Lb-FABP conserves the 12 characteristic residues present in all Lb-FABPs and absent in L-FABPs and presents the canonical fold characteristic of all the members of this protein family. Eight out of the 12 conserved residues point to the lipid-binding cavity of the molecule. In contrast, most of the 25 L-FABP conserved residues are in clusters on the surface of the molecule. The helix-turn-helix motif shows both a negative and positive electrostatic potential surface as in rat L-FABP, and in contrast with the other FABP types. The mechanism of anthroyloxy-labeled fatty acids transfer from Lb-FABP to phospholipid membranes occurs by a diffusion-mediated process, as previously shown for L-FABP, but the rate of transfer is 1 order of magnitude faster. Toad Lb-FABP can bind two cis-parinaric acid molecules but only one trans-parinaric acid molecule while L-FABP binds two molecules of both parinaric acid isomers. Although toad Lb-FABP shares with L-FABP a broad ligand-binding specificity, the relative affinity is different.