N-terminal truncation of the scrapie-associated form of PrP by lysosomal protease(s): implications regarding the site of conversion of PrP to the protease-resistant state.

Scrapie and related transmissible spongiform encephalopathies result in the accumulation of a protease-resistant form of an endogenous brain protein called PrP. As an approach to understanding the scrapie-associated modification of PrP, we have studied the processing and sedimentation properties of protease-resistant PrP (PrP-res) in scrapie-infected mouse neuroblastoma cells. Like brain-derived PrP-res, the neuroblastoma cell PrP-res aggregated in detergent lysates, providing evidence that the tendency to aggregate is an intrinsic property of PrP-res and not merely a secondary consequence of degenerative brain pathology. The PrP-res species had lower apparent molecular masses than the normal, protease-sensitive PrP species and were not affected by moderate treatments with proteinase K. This suggested that the PrP-res species were partially proteolyzed by the neuroblastoma cells. Immunoblot analysis of PrP-res with a panel of monospecific anti-PrP peptide sera confirmed that the PrP-res species were quantitatively truncated at the N terminus. The metabolic labeling of PrP-res in serum-free medium did not prevent the proteolysis of PrP-res, showing that the protease(s) involved was cellular rather than serum-derived. The PrP-res truncation was inhibited in intact cells by leupeptin and NH4Cl. This provided evidence that a lysosomal protease(s) was involved, and therefore, that PrP-res was translocated to lysosomes. When considered with other studies, these results imply that the conversion of PrP to the protease-resistant state occurs in the plasma membrane or along an endocytic pathway before PrP-res is exposed to endosomal and lysosomal proteases.     

Photoperiod control of poplar bark storage protein accumulation

Bark storage proteins (BSPs) accumulate in the inner bark parenchyma of many woody plants during autumn and winter. We investigated the effect of a short-day (SD) photoperiod on the accumulation of the 32-kilodalton bark storage protein of poplar (Populus deltoides Bart. ex Marsh.) under controlled environmental and natural growing conditions. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis and protein gel blot analysis revealed that 10 days of SD exposure (8 hours of light) resulted in a 20% increase in the relative abundance of the 32-kilodalton bark storage protein of poplar. After 17 days of SD exposure, the 32-kilodalton bark storage protein accounted for nearly one-half of the soluble bark proteins. In natural field conditions, accumulation of the 32-kilodalton bark storage protein was observed to start by August 18 (daylength 14.1 hours). Immunoprecipitation of in vitro translation products with anti-BSP serum revealed that the SD protein accumulation was correlated with changes in the pool of translatable mRNA. A survey of poplar clones from different geographic origins revealed the presence of the 32-kilodalton BSP in the dormant bark of all the clones tested. These results demonstrate that a SD photoperiod induces, whether directly or indirectly, rapid changes in woody plant gene expression, leading to the accumulation of BSP.     

Cryopreservation of Digitalis lanata Ehrh. cell cultures: Preculture and freeze tolerance

Cryopreservation experiments were performed with Digitalis lanata cell cultures. The main stress was laid on the behaviour of the cells during the preculture period and the capacity of various preculture additives to induce freeze tolerance. The following compounds were used as preculture additives: trehalose, mannitol, sucrose, melibiose, proline, and sorbitol. They are listed in the order of their respective efficiency. Using trehalose, high post-thaw viability rates were achieved and the cells resumed growth after a short lag period. Melibiose was used as a preculture additive for the first time. Its suitability was in the range of that of sucrose. Proline and sorbitol were not able to induce freeze tolerance in Digitalis cells. Cell viability showed a considerable decrease at the beginning of the preculture period. This reduction was found to be transient in the presence of trehalose, mannitol, sucrose, and melibiose. The damaging effects of proline and sorbitol were too severe to be compensated for by the cells. The PAL activity increased markedly in the presence of proline, whereas the trehalose-treated and the control cells behaved nearly identical to one another.     

Molecular characterization of medium-chain acyl-CoA dehydrogenase (MCAD) deficiency: identification of a lys329 to glu mutation in the MCAD gene,and expression of inactive mutant enzyme protein in E. coli

Summary A series of experiments has established the molecular defect in the medium-chain acyl-coenzyme A (CoA) dehydrogenase (MCAD) gene in a family with MCAD deficiency. Demonstration of intra-mitochondrial mature MCAD indistinguishable in size (42.5-kDa) from control MCAD, and of mRNA with the correct size of 2.4 kb, indicated a point-mutation in the coding region of the MCAD gene to be disease-causing. Consequently, cloning and DNA sequencing of polymerase chain reaction (PCR) amplified complementary DNA (cDNA) from messenger RNA of fibroblasts from the patient and family members were performed. All clones sequenced from the patient exhibited a single base substitution from adenine (A) to guanine (G) at position 985 in the MCAD cDNA as the only consistent base-variation compared with control cDNA. In contrast, the parents contained cDNA with the normal and the mutated sequence, revealing their obligate carrier status. Allelic homozygosity in the patient and heterozygosity for the mutation in the parents were established by a modified PCR reaction, introducing a cleavage site for the restriction endonuclease NcoI into amplified genomic DNA containing G⁹⁸⁵. The same assay consistently revealed A⁹⁸⁵ in genomic DNA from 26 control individuals. The A to G mutation was introduced into an E. coli expression vector producing mutant MCAD, which was demonstrated to be inactive, probably because of the inability to form active tetrameric MCAD. All the experiments are consistent with the contention that the G⁹⁸⁵ mutation, resulting in a lysine to glutamate shift at position 329 in the MCAD polypeptide chain, is the genetic cause of MCAD deficiency in this family. We found the same mutation in homozygous form in 11 out of 12 other patients with verified MCAD deficiency.     

Expression of membrane activation antigens on murine B lymphocytes stimulated with lipopolysaccharide

The expression of two membrane glycoproteins, RL388 antigen and transferrin receptor (TfR), was examined on murine B cells stimulated with lipopolysaccharide (LPS) in vitro. Immunofluorescent staining with monoclonal antibodies and flow cytofluorometric analysis were used to monitor the expression of these markers as a function of the time in culture, the state of membrane Ia antigen expression, the position in cell cycle, and the degree of B-cell differentiation. Freshly explanted splenic B cells expressed low levels of RL388 antigen and TfR. Following LPS stimulation, increased expression of RL388 antigen was detectable by 8 to 12 hr of culture, a time span characterized by increased Ia antigen expression, blast transformation, and G0 to G1 phase transition. The increased expression of TfR was apparent later and correlated with entry into late G1 phase and the onset of S phase. LPS-stimulated cell cultures treated with actinomycin D (G0/G1 block) exhibited increased expression of Ia antigen, but neither RL388 antigen nor TfR, whereas hydroxyurea treatment (G1/S block) allowed expression of all three markers. These results indicate that hyperexpression of RL388 antigen and TfR occurs during G1 phase and that these events are subsequent to Ia antigen hyperexpression. Finally, B cells in late G1 through M phase of the cell cycle simultaneously express high levels of RL388 antigen and TfR. These findings suggest that the expression patterns of RL388 antigen and TfR might be useful parameters for defining compartments of the murine B-cell cycle.     

Prostaglandin binding activity and myoblast fusion in aggregates of avian myoblasts

Myoblast aggregates provide a system for studying cell interactions which have several advantages over standard, stationary cultures. In gyrotory rotation, aggregate size can be controlled and is independent of cell migration. In muscle aggregates, fibroblasts are excluded, yet myoblast differentiation and fusion occur in a highly synchronous fashion. Specific PG binding occurs in chick or quail myoblast aggregates: in chick the peak of binding is at 35-36 hr. Aggregation is complete 16 hr before PG binding activity appears. This suggests either that gyrotory aggregation is not identical to myoblast recognition, or that PG binding activity occurs subsequent to myoblast recognition. Myoblast aggregates begin to release PG before 18 hr. The amount detected remains constant until binding begins at 34 hr when PG binding to the aggregates begins. Thus, both the release of PG and PG receptor activity are characteristics of the myoblasts and release of prostaglandin precedes appearance of the binding activity. As a first step in identifying the PG receptor and determining its appearance on the myoblast cell surface, we have prepared antisera against myoblast surfaces which blocks receptor-ligand interaction and have absorbed it against both peripheral and intrinsic membrane fractions. The results indicate that the PG receptor is a myoblast peripheral membrane macromolecule.     

Sequence homologies of glucose-dehydrogenases of Bacillus megaterium and Bacillus subtilis

The sequence homologies of the glucose dehydrogenase subunits of B. megaterium and B. subtilis are compared. From the known B. megaterium aminoacid sequence and the base sequence of the cloned B. subtilis structural gene we predict the B. megaterium structural glucose dehydrogenase gene. Assuming the minimal mutational changes to convert one gene into the other 23 transitions, 30 transversions, 1 inversion, 3 insertion-deletions, but no frameshifts are postulated necessary to interconvert the structural genes. The homology of both enzyme subunits of 85% reflects the close evolutionary distance between B. subtilis and B. megaterium.     

Immunoreactivity and ouabain-dependent phosphorylation of (Na+ + K+)-adenosinetriphosphatase catalytic subunit doublets

Sodium dodecyl sulfate-polyacrylamide gel electrophoresis with 6% polyacrylamide was used to resolve the 100-kDa catalytic (alpha subunit) polypeptide of (Na+ + K+)-adenosinetriphosphatase from various tissues. The catalytic subunit was identified on immunoblots with antisera against mouse brain catalytic subunit and lamb kidney holoenzyme. Immunoblots and Coomassie Blue-stained companion gels showed double species of the 100-kDa subunit in sucrose gradient fractions of mouse brain and kidney, bovine grey and white matter, purified lamb kidney and duck salt gland holoenzyme, electroplax microsomes, and NaI-extracted microsomes of goldfish and rat brain. The apparent molecular mass differences between the two species in each tissue all ranged between 5 and 8 kDa. Both forms in rat brain and lamb kidney enzyme contain common epitopes reactive with antibodies immunoaffinity-purified on either species from mouse brain. In addition, ouabain-dependent acid-stable inorganic phosphate incorporation was tested with mouse brain, lamb kidney, and electroplax enzyme. Ouabain-dependent phosphorylation was demonstrated in both species in lamb kidney and electroplax and in the larger of the two forms in mouse brain. These results suggest that double species of the phosphorylatable subunit are present generally in epithelial as well as excitable tissues and in fish and avian as well as mammalian species. Work is needed to elucidate their qualitative and quantitative characteristics in different tissues.     

Constant Phycobilisome Size in Chromatically Adapted Cells of the Cyanobacterium Tolypothrix tenuis, and Variation in Nostoc sp

Phycobilisomes of Tolypothrix tenuis, a cyanobacterium capable of complete chromatic adaptation, were studied from cells grown in red and green light, and in darkness. The phycobilisome size remained constant irrespective of the light quality. The hemidiscoidal phycobilisomes had an average diameter of about 52 nanometers and height of about 33 nanometers, by negative staining. The thickness was equivalent to a phycocyanin molecule (about 10 nanometers). The molar ratio of allophycocyanin, relative to other phycobiliproteins always remained at about 1:3. Phycobilisomes from red light grown cells and cells grown heterotrophically in darkness were indistinguishable in their pigment composition, polypeptide pattern, and size. Eight polypeptides were resolved in the phycobilin region (17.5 to 23.5 kilodaltons) by isoelectric focusing followed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Half of these were invariable, while others were variable in green and red light. It is inferred that phycoerythrin synthesis in green light resulted in a one for one substitution of phycocyanin, thus retaining a constant phycobilisome size. Tolypothrix appears to be one of the best examples of phycobiliprotein regulation with wavelength. By contrast, in Nostoc sp., the decrease in phycoerythrin in red light cells was accompanied by a decrease in phycobilisome size but not a regulated substitution.     

Anatomical and physiological characteristics of individual neurones in the central antennal pathway of insects

Signals of tens up to hundreds of thousands of (mostly olfactory) receptor cells on an insect antenna are switched to a comparatively low number of neurones in the antennal lobe of the deutocerebrum in circumscribed units of neuropile, the glomeruli. Each glomerulus is connected via its output neurone to two separate neuropiles (calyces of mushroom body, and lateral lobe) of the protocerebrum. Local interneurones interconnect between the glomeruli. Certain modes of convergence between receptors and central neurones provide for a very high sensitivity of the latter to certain odours and their sensitivity for complex odour stimuli, and in many cases for a marked multimodality. Anatomical and physiological data are given especially for pheromone sensitive neurones and their projections.