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PubMed1987

Characterization and use of polyclonal antibody to Na+,K+-ATPase: immunocytochemical localization in salt glands of the duck.

The amount of Na+,K+-ATPase of the avian salt gland increased concomitantly with plasma membrane surface area during salt feeding of ducklings (adaptation), and both enzyme content and membrane surface area decreased upon return to fresh water (deadaptation). In a further study of the enzyme, a marker for plasma membrane biogenesis, polyvalent antibodies were raised to the denatured alpha-subunit of the purified ATPase. Antisera did not inhibit enzymatic activity but immunoprecipitated the phosphorylated intermediate of the alpha-subunit. Furthermore, the alpha-subunit, which was not glycosylated, was immunoprecipitated from homogenates of tissue slices metabolically labelled with [35S]-methionine, using antisera raised against either duck salt gland or dog kidney alpha-subunit. The former antisera also recognized the alpha-subunit in the brain, heart, kidney, liver, intestine and skeletal muscle of the duck. Immunocytochemistry with the antisera raised to the duck salt gland alpha-subunit revealed reaction at basolateral as well as apical plasma membrane in the duck salt gland principal cells, with essentially no deposits on peripheral cells, fibroblasts, erythrocytes, endothelial cells and neural elements. Within the principal cells, immunolabelling was also detected on small vesicles, multivesicular bodies and lysosomes; deposits on extracellular debris and vesicles in the lateral and lumenal spaces were also apparent. The labelling patterns were qualitatively but not quantitatively similar in salt glands of control, adapted and deadapted ducklings, and are discussed in the context of a model for plasma membrane biogenesis and turnover in which degradative events may play a major role.

Adaptation, Physiological↗
PubMed1999

Localisation of phosphatidylethanolamine-binding protein in the brain and other tissues of the rat.

Phosphatidylethanolamine-binding protein (PEBP) is a highly-conserved 21- to 23-kDa basic protein that shows preferential affinity in vitro for phosphatidylethanolamine. Previous studies have focussed on PEBP in the brain and male reproductive tract where it has been proposed to play a role in membrane biogenesis. In the present more comprehensive study, rat PEBP transcripts and protein have been found to be expressed in all tissues examined, although the levels vary considerably between tissues. However, at the cellular level, PEBP expression is enigmatic, being restricted to a diverse range of highly specialised neuronal and non-neuronal cell types. The nature of this diversity, ranging from oligodendrocytes to plasma cells, whilst not precluding a role for PEBP in membrane biogenesis in some cell types, would imply that this is not the major function in others.

Adrenal Glands↗
PubMed1999

1,2-sn-Diacylglycerol in plant cells: Product, substrate and regulator.

1,2-sn-Diacylglycerol (DAG) is a family of lipidic molecular species varying in the lengths and desaturation levels of acyl groups esterified at positions sn-1 and sn-2 of the glycerol backbone. In plant cells, DAG originating from plastid and from extraplastidial membranes have distinct molecular signatures, C18/C16 and C18/C18 structures, respectively. Under normal conditions, DAG is consumed nearly as fast as it is produced and is therefore a transient compound in the cell. In plants, DAG proved to be the most basic ingredient for cell membrane biogenesis and fat storage, but we still lack formal evidence to assert that DAG is also an intracellular messenger, as demonstrated for animals. From the biochemical and molecular comparisons of the best known DAG-manipulating proteins of prokaryotic and eukaryotic cells (phosphatidate phosphatases, diacylglycerol kinases, MGDG synthase, protein kinase C, etc.) this review aims to identify general rules driving DAG metabolism, and emphasizes its unique features in plant cells. DAG metabolism is an intricate network of local productions and utilizations: many isoenzymes can catalyse similar DAG modifications in distinct cell compartments or physiological processes. The enzymatic- or binding-specificity for DAG molecular species demonstrates that discrete DAG molecular subspecies fluxes are finely controlled (particularly for C18/C16 and C18/C18 structures in plastid membrane biogenesis). Eventually, this review stresses the diversity of structures and functioning of DAG-manipulating proteins. As a consequence, because DAG metabolism in plants is unique, the deciphering of genomic information cannot rely on homology searches using known prokaryotic, animal or yeast sequences, but requires sustained efforts in biochemical and molecular characterizations of plant DAG-manipulating proteins.

Journal Article↗
PubMed2005

Characterization of RP 333, a gene encoding CapD of Rickettsia prowazekii with UDP-glucose 4-epimerase activity.

The genetic mechanism of membrane assembly in Rickettsia prowazekii, the causative agent of epidemic typhus, is unknown. Recent progress in genomics of this small intracellular bacterium prompted us to explore membrane biogenesis as it pertains to identification and characterization of gene products that are of importance in polysaccharide biosynthesis. We chose to define the function of the R. prowazekii capD gene (RP 333) product designated as a putative epimerase. We detected a capD transcript in yolk sacs infected with R. prowazekii at ten days post-infection. The capD gene was PCR amplified and cloned into the entry vector pENTR/SD/D-TOPO and transferred to a low copy arabinose-inducible pBAD/Myc-HisA expression plasmid constructed in our laboratory. The corresponding recombinant protein (CapD) was expressed in PL2, a galE28 mutant of Escherichia coli, and has been shown to epimerize UDP-galactose to UDP-glucose without the addition of NAD+. CapD characterization is important for defense strategies targeted towards design of an R. prowazekii vaccine, generation of new antibiotics, and opening the way for research in membrane biogenesis with respect to the parasitic lifestyle of Rickettsia.

Base Sequence↗
PubMed1982

Biogenesis of membrane lipoproteins in Escherichia coli.

Globomycin-resistant mutants of Escherichia coli have been isolated and partially characterized. Approximately 2-5% of these mutants synthesize structurally altered Braun's lipoprotein. The majority of these mutants contain unprocessed and unmodified prolipoprotein. One mutant is found to contain modified, processed, but structurally altered lipoprotein. Mutants containing lipid-deficient prolipoprotein or lipoprotein also show increased resistance to globomycin. These results suggest that the inhibition of processing of modified prolipoprotein by globomycin may require fully modified prolipoprotein as the biochemical target of this novel antibiotic. Our failure to isolate mutant containing cleaved but unmodified lipoprotein among globomycin-resistant mutants is consistent with the possibility that modification of prolipoprotein precedes the removal of signal sequence by a unique signal peptidase. Recent evidence indicates that the minor lipoproteins in the cell envelope of E. coli are also synthesized as lipid-containing prolipoproteins and the processing of these prolipoproteins is inhibited by globomycin. These results suggest the existence of modifying enzymes in E. coli which would transfer glyceryl and fatty acyl moieties to cysteine residues located in the proper sequences of the precursor proteins. This speculation is confirmed by our demonstration that Bacillus licheniformis penicillinase synthesized in E. coli as well as in B. licheniformis is a lipoprotein containing glyceride-cysteine at its NH2-terminus.

Anti-Bacterial Agents↗
PubMed1975

Biogenesis of membrane lipids: mutants of Escherichia coli with temperature-sensitive phosphatidylserine decarboxylase.

Phosphatidylserine decarboxylase catalyzes the last step in the pathway leading to phosphatidylethanolamine, the principal membrane lipid of E. coli. Mutants of E. coli have now been isolated in which this enzyme is theramolabile. The structural gene for phosphatidylserine decarboxylase (psd gene) is closely linked to the pur A locus at about 83 min on the standard map of the E. coli chromosome. When a mutant with thermolabile decarboxylase is incubated at 42 degrees, growth ceases, but only after a substantial fraction (20-40%) of the total phospholipid of the cell has been replaced by phosphatidylserine. Examination of such mutants with altered content of phospholipids may shed light on the role of specific phospholipids in membrane function.

Carboxy-Lyases↗
PubMed1974

Renewal of glycerol in the visual cells and pigment epithelium of the frog retina.

The renewal of glycerol in the visual cells and pigment epithelium of the frog retina was studied by autoradiographic analysis of animals injected with [2-(3)H]glycerol. Assay of chloroform:methanol extracts showed that the labeled precursor was used mainly in lipid synthesis, although there was also some utilization in the formation of protein. Radioactive glycerol was initially concentrated in the myoid portion of rods and cones, indicating that this is the site of phospholipid synthesis in visual cells. The glycogen bodies (paraboloids) of accessory cones were also heavily labeled, suggesting the diversion of some glycerol into glycogenic pathways. In the pigment epithelium, only the oil droplets became significantly radioactive. The outer plexiform layer (which contains the visual cell synaptic bodies) and the cone oil droplets gradually accumulated considerable amounts of labeled material. Within 1-4 h, labeled molecules began to appear in the visual cell outer segments, evidently having been transported there from the myoid portion of the inner segment. Most of these were phospholipid molecules which became distributed throughout the outer segments, presumably replacing comparable constituents in existing membranes. In rods only, there was also an aggregation of labeled material at the base of the outer segment due to membrane biogenesis. These highly radioactive membranes, containing labeled molecules of lipid and protein, were subsequently displaced along the rod outer segments due to repeated membrane assembly at the base. The distribution of radioactivity supported the conclusion that membrane renewal by molecular replacement is more rapid for lipid than it is for protein.

Animals↗
PubMed1987

Contribution of immunogold labelling to study of the outer membrane of gram-negative bacteria.

The immunogold labelling technique is beginning to make a significant contribution to the study of several biological systems. In the case of Gram-negative bacteria, immunogold labelling performed either on whole cells or on thin sections has recently begun to facilitate the study of outer membrane biogenesis, the topology of membrane proteins, and protein export.

Antigens, Bacterial↗
PubMed1994

Biogenesis: plasma membrane calcium ATPase: 15 years of work on the purified enzyme.

The plasma membrane calcium pump is the system that ejects Ca2+ out of eukaryotic cells: this is documented in all animal and plant cells, although knowledge on the latter is only now beginning to be established. Information on lower eukaryotic cells, e.g., yeast, is still scarce, but it also is beginning to develop. The pump shares the catalytic properties of ion-motive ATPases of the P-type family, but has distinctive regulation properties: it is modulated by calmodulin, acidic phospholipids, a number of protein kinases, possibly by the interaction of calcium with its COOH-terminal region, and by aggregation (dimerization) through the calmodulin binding domain. The latter acts as an endogenous inhibitor of pump activity, much as phospholamban does for the sarcoplasmic reticulum pump. The analogy of the regulation mechanisms of the two pumps is heightened by the finding that phosphorylation of the calmodulin binding domain by protein kinase C removes its autoinhibiting function, as other kinases do in the case of phospholamban. The pump is the product of a family of four genes located on different human chromosomes. The isoform diversity is dramatically enhanced by alternative splicing of the transcripts, occurring at "hot spot" A (NH2-terminal) and C (COOH-terminal). At present more than 20 different transcripts with striking tissue and developmental specificity have been detected.

Amino Acid Sequence↗
PubMed2003

Induction of protective immunity against Schistosoma mansoni via DNA priming and boosting with the large subunit of calpain (Sm-p80): adjuvant effects of granulocyte-macrophage colony-stimulating factor and interleukin-4.

Considerable morbidity and mortality result from schistosomiasis, an affliction affecting an estimated 200 million people. Although schistosomicidal drugs and other control measures (including public hygiene and snail control) exist, the advent of an efficacious vaccine remains the most potentially powerful means for controlling this disease. We have targeted a vaccine candidate (large subunit of calpain, Sm-p80) because of its consistent immunogenicity, protective potential, and integral role in surface membrane biogenesis of schistosomes. Since surface membrane renewal appears to be one of the major phenomena employed by schistosomes to evade the host's immune system; an immune response directed against Sm-p80 should render the parasite susceptible to immune clearance from the host by both providing a focus of attack and by potentially impairing the membrane repair process. In the present study, we have employed DNA immunization protocols using Sm-p80 with plasmids encoding granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin-4 (IL-4). Sm-p80 by itself provided 39% protection (P = < or =0.0001) against challenge infection in C57BL/6 mice. This protection was increased to 44% (P = < or =0.0001) when the plasmid encoding GM-CSF was coadministered with Sm-p80 DNA. Coinjection of plasmid DNA encoding IL-4 with Sm-p80 DNA yielded a protection level of 42% (P = < or =0.0001). Statistically, the protection conferred by including GM-CSF, but not IL-4, was significantly greater than that when only Sm-p80 was used. Sm-p80 DNA by itself elicited strong responses that include IgG2A and IgG2B antibody isotypes. The introduction of GM-CSF DNA with Sm-p80 DNA led to distinct increases in total IgG and IgG1 titers, whereas the coadministration of IL-4 DNA with Sm-p80 DNA resulted in a slight elevation of IgG1 and IgG3 titers and in some reduction of IgG2A and IgG2B titers. Our data again indicate that Sm-p80 can be an excellent candidate for a schistosomiasis vaccine.

Adjuvants, Immunologic↗
PubMed1996

Biogenesis of polytopic membrane proteins: membrane segments of P-glycoprotein sequentially translocate to span the ER membrane.

The initial steps in the biogenesis of membrane proteins parallel those of secretory proteins. However, membrane proteins contain a signal to stop translocation across the membrane. For polytopic membrane proteins, those with multiple transmembrane segments, little is known of the temporal sequence or relationship between synthesis of the nascent proteins, translocation, folding, and integration of the membrane segments into the bilayer. Here we demonstrate that latent membrane segments translocate sequentially as they emerge from the ribosome and do not accumulate on the cytosolic side to form loops, or larger structures, prior to translocation across the membrane.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1994

Location of Golgi membranes with reference to dividing nuclei in syncytial Drosophila embryos.

The role of cytoskeletal elements in the cellularization of syncytial Drosophila embryos is becoming evident; however, the distribution and role of organelles such as the Golgi complex, essential for membrane biogenesis, remain unknown. We have cloned a Golgi-membrane-associated polypeptide, beta-COP, from Drosophila. Immunocytochemical studies of syncytial Drosophila embryos with anti-Drosophila beta-COP antibody reveal that Golgi membranes are spatially segregated from the rapidly dividing nuclei. In early embryos, the Golgi membranes are located in the embryonic cortex and nuclei are confined to the core. This distribution of Golgi membranes may serve in preparation of the embryonic cortex for the accommodation of nuclei upon their eventual migration to the cortex and in biogenesis of the excessive plasma membrane needed for cellularization of syncytial embryos.

Amino Acid Sequence↗
PubMed1978

Cellular responses to surface binding and internalization of concanavalin A. An electron microscopic investigation on the problem of membrane cycling.

Monolayer cultures of normal and diethylnitrosamine-transformed rat liver cells were labeled in situ with Con A-HRP or ferritin-conjugated Con A. Ligand-induced redistribution with simultaneous internalization of labeled membrane areas occurred in normal as well as in transformed cells when they were reincubated with PBS at 37 degrees C for different periods of time (from 5 min up to 3 hrs). Compared to normal cells, these afore mentioned processes were accelerated in transformed cells. Internalization in normal and transformed cells resulted in a recycling of labeled plasma membrane areas in the Golgi region with the label being finally accumulated in elements which correspond mostly, but not exclusively, to GERL. Then formation of phagolysosomes and multivesiculated bodies occurred whose labeled content was exocytized after fusion with the plasma membrane. This suggested that the internalized plasma membrane areas were at least partly degraded. The relabeling of some parts of the plasma membrane by extruded lysosomal content indicates that at least some Con A molecules are still biological active. Membrane internalization by endocytosis after binding of Con A obviously causes an increased of membrane biogenesis and exocytosis, thus compensating for membrane removal. This is suggested by the vacuolization and enlargement of unlabeled (not in recycling involved) Golgi apparatus. It may indicate a differential functional role of the Golgi apparatus in membrane turnover in the same cell. The fusion of phagolysosomes with the plasma membrane and the insertion of phagolysosomal membrane into the plasma membrane might be another compensatory mechanism.

Animals↗
PubMed1996

Biogenesis of polytopic membrane proteins: membrane segments assemble within translocation channels prior to membrane integration.

The initial steps in the biogenesis of membrane proteins parallel that of secretory proteins. The translocation of membrane proteins, however, must be interrupted prior to the complete traversal of the membrane. This is followed by their folding and integrating into the lipid bilayer. We have previously shown that as each latent transmembrane segment (TMS) in a polytopic membrane protein emerges from the ribosome, it sequentially translocates across the membrane. Here we demonstrate that these translocated TMSs can be extracted from the membrane with urea. This suggests that nascent TMSs do not integrate into the bilayer as they achieve a transmembrane topography. The integration is delayed until after the protein is synthesized and released from the ribosome. Prior to insertion into the bilayer, these TMSs appear to be stabilized by salt-sensitive electrostatic bonds within an aqueous-accessible compartment.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1992

Membrane protein insertion into the endoplasmic reticulum--another channel tunnel?

The synthesis of biological membranes requires the insertion of proteins into a lipid bilayer. The rough endoplasmic reticulum of eukaryotic cells is a principal site of membrane biogenesis. The insertion of proteins into the membrane of the endoplasmic reticulum is mediated by a resident proteinaceous machinery. Over the last five years several different experimental approaches have provided information about the components of the machinery and how it may function.

Animals↗
PubMed2001

Pse1/Kap121-dependent nuclear localization of the major yeast multidrug resistance (MDR) transcription factor Pdr1.

Pdr1 and Pdr3 are two very similar transcription factors that mainly control membrane biogenesis by adjusting the production of different membrane proteins, such as different ABC or major facilitator superfamily (MFS) transporters. We observed that the pse1-1 mutation in the importin/beta-karyopherin Pse1/Kap121 specifically induced the cytoplasmic localization of Pdr1, but not that of Pdr3. Interactions between Pse1 and Pdr1 could be observed in vivo, and a short peptide of 44 amino acids from Pdr1 was shown to contain the information necessary and sufficient for Pse1-dependent nuclear import. This Pdr1-NLS sequence, absent in Pdr3, although rich in serine and tyrosine, is different from the Pse1-dependent nuclear localization signal (NLS) of Pho4. Furthermore, we showed that Pse1/Kap121 is likely to be the sole import receptor for the regulator Pdr1. Together, these new observations underscore the diversity of cellular processes that address to the nucleus two very similar transcription factors involved in the control of the same phenotype, thus securing their function in the cell.

Amino Acid Sequence↗