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Biomedical subjects

A Loewy

Publications and source records attributed to A Loewy.

18 recordsLinked to original sources
PubMed1995

The 6-kilodalton membrane protein of Semliki Forest virus is involved in the budding process.

Alphavirus genomes encode a small hydrophobic protein of 6 kDa (the 6K protein) that is expressed as part of a large polyprotein containing the sequences of the two virus transmembranal glycoproteins which form the spikes of the infectious particle. Although made in amounts equivalent to those of the glycoproteins, very little of the 6K protein is found in secreted infectious virions. The role of this protein in virus replication and structure has been studied by use of a variety of mutationally altered forms of 6K, which yield phenotypically distinct viruses. A complete deletion of the gene encoding the 6K protein (delta 6K) of Semliki Forest Virus (SFV) has been constructed from an SFV infectious cDNA and the transcribed RNA-produced progeny virus that closely resembled the normal virus (P. Liljeström, S. Lusa, D. Huylebroeck, and H. Garoff, J. Virol. 65:4107-4113, 1991). Further studies of this mutant have now been performed, and they show that growth of delta 6K has a strong dependency on its host cell, varying from 2 to 50% of the rate of formation of the wild-type SFV. Mammalian cells are much more defective than insect and avian cells in replication of the delta 6K mutant. This mutant is not defective in formation and transport of the glycoproteins or in production of nucleocapsids, which accumulate at the plasma cell membrane in infected BHK cells. The major defect, thus, is in the final assembly and budding of new virus. In BHK cells infected with the delta 6K strain, a relatively large fraction of the total infectious virus formed can be recovered by osmotic lysis of exhaustively washed cells. Infectious SFV totally lacking 6K is identical to wild-type SFV in the early stages of virus replication, i.e., binding and uptake. The particles themselves are more thermolabile than those of wild-type SFV, suggesting that the 6K protein may be a part of the structure of wild-type virus or that the slower budding leads to an altered configuration of the trimeric spikes. These data support other studies that implicate the 6K protein as an important but nonessential component in the assembly and budding of the alphavirus particle, perhaps by affecting the packing of the glycoproteins and their interactions with membrane lipid.

Animals↗
PubMed1991

The major 35S-methionine-labeled rapidly transported protein (superprotein) is identical to SNAP-25, a protein of synaptic terminals.

Superprotein is a rapidly axonally transported protein that is conspicuously labeled with 35S-methionine supplied to the cell bodies of retinal ganglion cells. Superprotein candidates are apparent among the rapidly transported proteins of many neurons from the CNS and PNS, including cranial, sympathetic, sensory, and motor neurons from mammals, fish, and amphibians. To determine the identity of Superprotein, we purified it from rabbit visual system and spinal cord and determined the amino acid sequence of seven of its tryptic peptides. The sequence shows that Superprotein is SNAP-25, a protein recently predicted from a cDNA sequence; SNAP-25 has been reported to be concentrated in the synaptic terminals of a selected population of CNS neurons. We measured the amount of radioactivity associated with Superprotein in tissue containing axons (optic tract) and synaptic terminals (superior collicules) of rabbit retinal ganglion cells. Labeled Superprotein disappeared from the superior colliculus more rapidly than another protein (synapsin I-like protein) that is concentrated in synaptic terminals. These results serve to unite the observations on the synthesis, distribution, metabolism, and axonal transport of Superprotein with observations of SNAP-25 and its mRNA.

Animals↗
PubMed1990

Purification of the growth-associated protein GAP-43 by reversed phase chromatography: amino acid sequence analysis and cDNA identification.

GAP-43 is a neuronal phosphoprotein. Increased synthesis and axonal transport of GAP-43 has been associated with axon growth, and altered phosphorylation of GAP-43 has been associated with changes in synaptic efficacy. Here we report a rapid and effective procedure employing reverse-phase HPLC for the purification of GAP-43 from rat brain. To characterize the protein purified by this procedure, we generated proteolytic fragments and determined their amino acid sequences. These directly determined sequences, corresponding to 56% of the GAP-43 amino acids, confirm recently reported sequences deduced from the nucleotide sequences of cDNAs. Using oligonucleotide probes constructed according to these amino acid sequences, we identified GAP-43 cDNAs in a library prepared from neonatal rat superior cervical ganglion cells. One of these cDNAs was 1.1 kB in size; it hybridized specifically with a 1.5 kB RNA from brain, but not from liver, and contained the entire coding sequence for GAP-43. This cDNA differed from recently reported cDNAs in its 3' untranslated region.

Amino Acid Sequence↗
PubMed1986

Topographic localization of the heparin-binding domain of the neural cell adhesion molecule N-CAM.

Previous studies have reported that the cell-binding region of the neural cell adhesion molecule (N-CAM) resides in a 65,000-D amino-terminal fragment designated Frl (Cunningham, B. A., S. Hoffman, U. Rutishauser, J. J. Hemperly, and G. M. Edelman, 1983, Proc. Natl. Acad. Sci. USA, 80:3116-3120). We have reported the presence of two functional domains in N-CAM, each identified by a specific mAb, that are required for cell-cell or cell-substratum adhesion (Cole, G. J., and L. Glaser, 1986, J. Cell Biol., 102:403-412). One of these domains is a heparin (heparan sulfate)-binding domain. In the present study we have determined the topographic localization of the heparin-binding fragment from N-CAM, which has been identified by our laboratory. The B1A3 mAb recognizes a 25,000-D heparin-binding fragment derived from chicken N-CAM, and also binds to a 65,000-D fragment, presumably Frl, produced by digestion of N-CAM with Staphylococcus aureus V8 protease. Amino-terminal sequence analysis of the isolated 25,000-D heparin-binding domain of N-CAM yielded the sequence: Leu-Gln-Val-Asp-Ile-Val-Pro-Ser-Gln-Gly. This sequence is identical to the previously reported amino-terminal sequence for murine and bovine N-CAM. Thus, the 25,000-D polypeptide fragment is the amino-terminal region of the N-CAM molecule. We have also shown that the B1A3 mAb recognizes not only chicken N-CAM but also rat and mouse N-CAM, indicating that the heparin-binding domain of N-CAM is evolutionarily conserved among different N-CAM forms. Additional peptide-mapping studies indicate that the second cell-binding site of N-CAM is located in a polypeptide region at least 65,000 D from the amino-terminal region. We conclude that the adhesion domains on N-CAM identified by these antibodies are physically distinct, and that the previously identified cell-binding domain on Frl is the heparin-binding domain.

Amino Acid Sequence↗
PubMed1983

Experimental use of fibrin tissue adhesive in middle ear surgery.

The biocompatibility of a new tissue adhesive was tested. Its major advantages are adhesions, hemostasis, and the promotion of wound healing. In experimental surgery on 43 middle ears of chinchillas, documented by histological evidence obtained 45 days after operation, the validity of the following two hypotheses was established. That fibrin tissue adhesive placed upon the footplate of the stapes is biologically compatible, biodegradable and does not cause toxic, inflammatory or foreign body reactions, or other tissue damage to middle ear structures. That a small piece of bone glued on the long process of the incus with fibrin tissue adhesive shows permanent tissue union. In addition, in cases where the inner ear was accidentally opened by surgically subluxating the stapes and adhesive was free to enter the vestibule, evidence was obtained that there was no damage to inner ear structures. This finding deserves further investigation.

Animals↗
PubMed1979

Regulation of teichoic acid synthesis during phosphate limitation.

Bacillus subtilis W-23, when placed in phosphate-free medium, ceases to synthesize teichoic acid and synthesizes teichuronic acid. The enzymatic basis for the cessation of teichoic acid synthesis is the irreversible inhibition of the first membrane-bound enzyme involved in teichoic acid synthesis which catalyzes the reaction Undecapenol-P + UDP-GlcNAc leads to undecaprenol-P-P-GlcNAc + UMP.

Bacillus subtilis↗
PubMed1979

Facial nerve repair with tissue adhesive.

The facial nerve in dogs was exposed, transected, and repaired by either of two methods. Suture and a Silastic sheath was the control method, since a review of the literature suggests it gives the highest rate of success. A tissue adhesive (Histoacryl) was used as the experimental method. In both techniques, the surgical microscope was used. Thirteen nerves were repaired: seven with the adhesive and six with suture and Silastic sheath. Success was judged on two criteria: (1) observation of motion in the muscles that were innervated after electrical stimulation of the nerve proximal to the repair site and (2) evaluation of microanatomical continuity after removal of the repair site and preparation of slides and tissues staining. The two repair methods produced statistically equal results. The "adhesive" method can be performed with greater ease and is less time-consuming. The number of studies required for statistical reliability was determined by means of sequential analysis.

Animals↗
PubMed1979

Control of teichoic acid synthesis during phosphate limitation.

The synthesis of teichoic acids was examined in Bacillus subtilis Marburg grown under conditions of phosphate limitation. The results indicate that the inhibition of polyglycerolphosphate synthesis observed under these conditions is the result of two processes. The first process is reversible and is independent of new protein synthesis; the second process is irreversible and requires the synthesis of new protein. During growth, under conditions of phosphate limitation, there is a slow decrease in the level of CDP glycerol pyrophosphorylase activity which is by itself not sufficient to account for the decrease in the rate of polyglycerolphosphate synthesis.

Bacillus subtilis↗
PubMedDate not supplied

Neuronal cell-cell adhesion depends on interactions of N-CAM with heparin-like molecules.

Cell-cell interactions are of critical importance during neural development, particularly since the migration of neural cells and the establishment of functional interactions between growing axons and their target cells has been suggested to depend upon cell recognition processes. Neurone-neurone adhesion has been well studied in vitro, and is mediated in part by the neural cell adhesion molecule N-CAM. N-CAM-mediated cell-cell adhesion has been postulated to occur by a homophilic binding mechanism, in which N-CAM on the surface of one cell binds to N-CAM on a neighbouring cell. Studies in our laboratory have identified a cell surface glycoprotein, now known to be N-CAM, which participates in cell-substratum interactions in the developing chicken nervous system. Although this adhesion involves a homophilic binding mechanism, the binding of the cell surface proteoglycan heparan sulphate to the glycoprotein is also required. This raises the question of whether the binding of heparan sulphate to N-CAM is also required for cell-cell adhesion. Here we show that the binding of retinal probe cells to retinal cell monolayers is inhibited by heparin, a functional analogue of heparan sulphate, but not by chondroitin sulphate. Monoclonal antibodies that recognize two different domains on N-CAM, the homophilic-binding and heparin-binding domains, inhibit cell-cell adhesion. The heparin-binding domain isolated from N-CAM by selective proteolysis also inhibits cell-cell adhesion when bound to the probe cells.

Animals↗