Emergence of a surface immunoglobulin recycling process during B lymphocyte differentiation

Surface immunoglobulin (Ig)-mediated endocytosis has been investigated in rat B lymphocytes and plasma cells, using horseradish peroxidase (HRP)-labeled sheep anti-rat Ig Fab' fragment of antibody and HRP as monomeric ligands, respectively. Quantitative estimates of HRP activity associated either with plasma membrane or with endomembrane compartments were made in several experimental conditions. Binding of HRP-conjugate on B lymphocytes was followed by its endocytosis in combination with surface Ig, as shown by the progressive disappearance of plasma membrane-associated HRP activity. Between 1 and 6 h at 37 degrees C in presence of conjugate the total amount of cell-associated activity was constant. These results indicate that during this time no reappearance of surface Ig occurred by neosynthesis, by the expression of an intracellular pool or by the recycling in a free form of the previously internalized molecules. On the contrary, at saturating doses, internalization of HRP by anti-HRP plasma cells increased linearly with time at 37 degrees C in presence of antigen, when, during the same time, the plasma membrane HRP-binding capacity remained constant. Cycloheximide did not affect continuous HRP uptake. The existence of a large intracellular pool of receptors has been ruled out by experiments of removal of binding sites with pronase. In addition, monensin caused a progressive decrease in the number of surface receptors on plasma cells but not on B lymphocytes. Our data then indicate that, unlike B lymphocytes, plasma cells were able to recycle their surface Ig.     

Molecular evolution of the ZFY and ZNF6 gene families

Members of the ZFY and ZNF6 gene families have been cloned from species representing different taxa and different modes of sex determination. Comparisons of these genes show the ZFY-like and ZNF6 sequences to be strongly conserved across marsupials, birds, and lepidosaurians. Sequence analyzed by neighbor-joining indicated that both gene families are monophyletic with a high bootstrap value. Pairing of sequences from males and females of nonmammalian species showed there to be no significant difference between male and female sequences from a single species, consistent with autosomal locations. The molecular distances between murine Zfy-1, Zfy-2, and other ZFY-like sequences suggested that Zfy genes have undergone a period of rapid evolutionary change not seen in human ZFY.      

Saccharomyces cerevisiae as anodic biocatalyst for power generation in biofuel cell: influence of redox condition and substrate load

Bio (microbial) fuel cell (microbial fuel cell) with Saccharomyces cerevisiae as anodic biocatalyst was evaluated in terms of power generation and substrate degradation at three redox conditions (5.0, 6.0 and 7.0). Fuel cell was operated in single chamber (open-air cathode) configuration without mediators using non-catalyzed graphite as electrodes. The performance was further studied with increasing loading rate (OLRI, 0.91 kg COD/m³-day; OLRII, 1.43 kg COD/m³). Higher current density was observed at pH 6.0 [160.36 mA/m² (OLRI); 282.83 mA/m² (OLRII)] than pH 5.0 (137.24 mA/m²) and pH 7.0 (129.25 mA/m²). Bio-electrochemical behavior of fuel cell was evaluated using cyclic voltammetry which showed the presence of redox mediators (NADH/NAD⁺; FADH/FAD⁺). Higher electron discharge was observed at pH 6.0, suggesting higher proton shuttling through the involvement of different redox mediators. The application of yeast based fuel cell can be extended to treat high strength wastewaters with simultaneous power generation.     

Direct Selection of Monoclonal Phosphospecific Antibodies without Prior Phosphoamino Acid Mapping

In the current post-genomic era, large scale efforts are underway to functionally explore the proteome by assembling large antibody libraries. However, because many proteins are modified post-translationally to regulate their function, collections of modification-specific sensors are also needed. Here we applied a novel approach to select monoclonal phosphospecific antibodies directly from the full-length protein and without up-front phosphoamino acid identification. We chose as antigen GRASP65, a well studied Golgi phosphoprotein. Bacterially produced full-length protein was first incubated with mitotic cytosol, thus allowing modification by naturally occurring kinases, and then used directly for affinity-based antibody selection using a single chain variable fragment phagemid library. In less than 1 week, three distinct and highly functional monoclonal phosphospecific antibodies against two GRASP65 epitopes were obtained and subsequently characterized. The presented approach is carried out fully in vitro, requires no prior knowledge of the phosphoamino acid identity, and is fast and inexpensive. It therefore has great potential to be an attractive alternative to classic animal-based protocols for the selection of post-translation modification sensors and thus to become an invaluable tool in our quest to understand the proteome in all its complexity.In the current post-genomic era, large scale efforts are underway to study the emerging proteome. Because of their ability to bind their respective targets with extremely high specificity, antibodies are essential tools in this endeavor. In fact, non-profit organizations like the European “ProteomeBinders” Consortium (1) and the “Clinical Proteomic Technologies for Cancer” network (2) as well as commercial enterprises are currently sponsoring large projects to assemble all-inclusive antibody libraries.To regulate their function, many proteins are altered after their initial synthesis. Because such post-translational modifications change the physicochemical properties of a given protein, this further increases the complexity of the proteome. Therefore, the true challenge is to have not only all-inclusive antibody libraries but also to assemble collections of sensors, which specifically detect post-translational changes.One of the best studied modifications after polypeptide synthesis is reversible protein phosphorylation through the action of specific kinases and phosphatases. A plethora of cellular processes hinges upon the correct phosphorylation state of key regulators (3), and errors may result in cell death or malignancy (4). It is therefore not surprising that protein phosphorylation represents a very active area of research in the quest for new therapeutic cancer targets (5). Phosphospecific antibodies, first described over 25 years ago (6–8), represent key tools in the study of cellular processes regulated by phosphorylation. Their production, however, is relatively costly and time consuming.In our laboratory we have succeeded in obtaining highly functional, conformation-specific recombinant antibodies using the method of phage display (9, 10).⁵ This not only allowed us to follow the fate of proteins upon activation but also demonstrated that the diversity of available recombinant antibody libraries is sufficiently broad. We thus decided to use a similar approach for the selection of phosphospecific antibodies. We chose GRASP65 as the antigen, the predominant phosphoprotein of mitotic Golgi membranes (11). Careful studies have mapped several phospho-residues of this structural Golgi protein, and phosphospecific antibodies have been generated using classical methods (12–14). This study describes a novel approach, which allowed the direct selection and characterization of three distinct and highly functional monoclonal phosphospecific antibodies.     

Cytogenetic investigation of patients with primary amenorrhea

Primary amenorrhea refers to absence of spontaneous menarche even after the age of 16. Cytogenetic analysis in two cases with primary amenorrhea, short stature, poorly developed secondary sexual characteristics, and growth retardation were studied. Routine GTG-band analysis of metaphases from peripheral blood leucocytes revealed female karyotype with a 15(ps+) and an isochromosome of X, i(Xq), in one patient and 46,X, i(Xq), in another patient. Ascertainment of the karyotype aided in confirmation of the provisional diagnosis, a better phenotype-genotype correlation to understand clinical heterogeneity in genetic counseling.     

Retrograde traffic in the biosynthetic-secretory route: pathways and machinery

In the secretory pathway, the forward (anterograde) membrane flow is compensated by retrograde transport of proteins and lipids. Membrane recycling is required for the maintenance of organelle homeostasis and the re-use of components of the transport machineries for the generation of new transport intermediates. However, the molecular mechanisms and other cellular functions of retrograde traffic are still poorly understood. In recent years, a multitude of protein factors that function in the secretory pathway have been discovered, most of them originally suggested to play a role in forward trafficking. However, in many cases subsequent studies have revealed that these proteins participate (also) in retrograde traffic. It is likely that this shift will continue, reflecting the fact that the two pathways are intimately connected.     

Matrix metalloproteinases: old dogs with new tricks

The matrix metalloproteinase family in humans comprises 23 enzymes, which are involved in many biological processes and diseases. It was previously thought that these enzymes acted only to degrade components of the extracellular matrix, but this view has changed with the discovery that non-extracellular-matrix molecules are also substrates.     

CLIPR-59, a new trans-Golgi/TGN cytoplasmic linker protein belonging to the CLIP-170 family

The microtubule cytoskeleton plays a fundamental role in cell organization and membrane traffic in higher eukaryotes. It is well established that molecular motors are involved in membrane-microtubule interactions, but it has also been proposed that nonmotor microtubule-binding (MTB) proteins known as CLIPs (cytoplasmic linker proteins) have basic roles in these processes. We report here the characterization of CLIPR-59, a CLIP-170-related protein localized to the trans-most part of the Golgi apparatus. CLIPR-59 contains an acidic region followed by three ankyrin-like repeats and two CLIP-170-related MTB motifs. We show that the 60-amino acid-long carboxy-terminal domain of CLIPR-59 is necessary and sufficient to achieve Golgi targeting, which represents the first identification of a membrane targeting domain in a CLIP-170-related protein. The MTB domain of CLIPR-59 is functional because it localizes to microtubules when expressed as a fragment in HeLa cells. However, our results suggest that this domain is normally inhibited by the presence of adjacent domains, because neither full-length CLIPR-59 nor a CLIPR-59 mutant missing its membrane-targeting region localize to microtubules. Consistent with this observation, overexpression of CLIPR-59 does not affect the microtubule network. However, CLIPR-59 overexpression strongly perturbs early/recycling endosome-TGN dynamics, implicating CLIPR-59 in the regulation of this pathway.     

uDENN, DENN, and dDENN: indissociable domains in Rab and MAP kinases signaling pathways

DENN domains are found in a variety of signaling proteins but their exact function remains undefined. Some of the DENN-containing proteins, such as rat Rab3GEP (Rab3 GDP/GTP exchange protein) or mouse Rab6IP1 (Rab6 interacting protein 1) interact with GTPases of the Rab family. Others, such as human MADD (MAP (Mitogen-activated protein) kinase activating protein containing death domain) and human ST5 (Suppressor of tumoreginicity 5) gene products are involved in regulation of MAPKs (Mitogen-activated protein kinases) signaling pathways. Using a combination of profile-based and bidimensional analyses, we show here that DENN domains are much larger than described to date in domain databases, always encircled on both sides by more divergent domains, that we called uDENN and dDENN. These however share conserved amino acids which could play a key role in the DENN functions.