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PubMed1980

Properties of a calcium-activated protease in squid axoplasm which selectively degrades neurofilament proteins.

Axoplasm extruded from the giant axon of the squid contains Ca2+-activated proteases. The protease in the 100,000 x g of supernatant of axoplasm is very specific and degrades only the 200,000 MW, neurofilament protein (NF200), whereas the protease(s) in the pellet has a much wider range of substrate specificity. The activation of the supernatant protease is restricted to the Ca2+ ion, and no other divalent cation will substitute. The protease requires Ca2+ at a higher concentration than 0.5 mM for activation, and has a pH optimum of about 7.5. Degradation of the NF200 appears to proceed through a 100,000 MW and possibly a 47,000--50,000-MW intermediate form before degradation to TCA-soluble peptides. Activity of the protease is inhibited by divalent cation chelators, Cu2+ and Fe2+, sulphydryl inhibitors, and leupeptin. This specific Ca2+-activated protease in squid axoplasm has identical properties to Ca2+-activated proteases found in various non-neural tissues. Despite its narrow protein substrate specificity, Ca2+-activated protease purified from human platelets effectively degrades squid NF200, suggesting a possible structural relationship between platelet and muscle actin-binding proteins and neurofilament proteins.

Animals↗
PubMed1992

Transfer of molecules from glia to axon in the squid may be mediated by glial vesicles.

Although the transfer of glial proteins into the squid giant axon is well documented, the mechanism of the transfer remains unknown. We examined the possibility that the transfer involved membrane-bound vesicles, by taking advantage of the fact that the fluorescent compound, 3,6-acridinediamine, N,N,N,',N'-tetramethylmonohydride [acridine orange (AO)], rapidly and selectively stains vesicular structures in glial cells surrounding the giant axon. We labeled cleaned axons (1-3 cm long) by incubation for 1 min in filtered seawater (FSW) containing AO. Because the AO was concentrated in glial vesicular organelles, these fluoresced bright orange when the axon was examined by epifluorescence microscopy. To look for vesicle transfer, axoplasm was extruded from such AO-treated axons at various times after labeling. During the initial 15 min, an increasing number of fluorescent vesicles were observed. No further increases were observed between 15 and 60 min post AO. The transfer of the fluorescent vesicles into the axoplasm seemed to be energy dependent, as it was inhibited in axons treated with 2 mM KCN. These results suggest that a special mode of exchange exists between the adaxonal glia and the axon, perhaps involving phagocytosis by the axon of small portions of the glial cells.

Acridine Orange↗
PubMed1994

Identification of a 70 kD protein with sequence homology to squid neurofilament protein in glial cells of the leech CNS.

A monoclonal antibody G39, generated against a protein extract of leech central nervous system, labels specific cell types in adult, embryonic, and regenerating preparations. The antibody stained glial cells, microglial cells, and connective tissue cells, but not neurons or muscle on cryosections. The staining pattern resembled that of an intracellular network. Affinity purification of the antigen revealed a 70 kD protein. Peptide sequencing showed significant homology of a stretch of 15 amino acids to squid neural filament protein. The same mAb G39 delineated glial cells as they formed during development of the CNS and showed that the giant neuropil glial cells appear before those in the packets. The antigen recognized by mAb G39 represents a nonneuronal intermediate filament of the leech Hirudo medicinalis found in various cell-types such as glia, microglia, and some cells of the connective tissue.

Amino Acid Sequence↗
PubMed1995

Antibodies to three chondroitin sulfate-containing proteoglycans in squid skin recognize hexa- or longer chondroitin oligosaccharides as major antigenic determinants.

The reactivities of antibodies to three squid skin proteoglycans with (a) chondroitin-derived oligosaccharides and chondroitin sulfate-derived disaccharides, (b) the proteoglycans and their constituents, and (c) chondroitin, chondroitin sulfate, and hyaluronic acid were studied with enzyme-linked immunosorbant assay inhibition tests. Immunization of rabbits with two chondroitin proteoglycans (ChPG I and ChPG II) and an oversulfated chondroitin sulfate proteoglycan (CSSPG) gave rise to highly reactive antisera which were mainly reactive with the glycosaminoglycans, the oligosaccharides, and the core proteins obtained after digestion of proteoglycans with chondroitinase AC. Inhibition of binding of antibodies to ChPG I, ChPG II, and CSSPG with chondroitin-derived oligosaccharides revealed that the minimal antigenically active structure was the hexasaccharide of chondroitin and that the respective octasaccharide was more active. Sulfated delta-disaccharides were not reactive with antibodies to ChPG I and II, whereas some reactivities (30% maximum inhibition) were obtained with antibodies to CSSPG. Chondroitin chains (80 kDa) of ChPG I and II were responsible for most of the reactivity with proteoglycans (78-95% maximum inhibition). Chemically desulfated chondroitin sulfate (12 kDa) showed considerable cross-reactivity with all antisera tested (62-68% maximum inhibition), whereas the nonsulfated molecule of hyaluronic acid and a hyaluronic acid fraction of 16 kDa were not reactive. The reactivities of antibodies with the proteoglycans' oligosaccharides and core proteins obtained by chondroitinase AC digestion were mainly due to the presence of nonsulfated chondroitin sulfate structures. This study clearly shows that the major antigenic determinants recognized by antibodies to squid skin proteoglycans, each containing chondroitin sulfates with different sulfation patterns, involve hexa- or larger chondroitin oligosaccharides.

Animals↗
PubMed1994

Novel fucose-rich glycosaminoglycans from squid ink bearing repeating unit of trisaccharide structure (-6GalNAc alpha 1-3GlcA beta 1-3Fuc alpha 1-)n.

Three fucose-rich glycosaminoglycans (GAGs), illexin A, illexin B and illexin C, were isolated from squid ink of Illex argentinus. The GAGs were obtained by the method of Actinase E digestion, DEAE Sephadex A-50 ion-exchange chromatography and Sephacryl S-300 gel filtration. They gave a single band on the electrophoresis using cellulose acetate membrane and contained equimolar ratios of Fuc, GlcA and GalNAc. Molecular weights of illexin A, illexin B, and illexin C were determined by Sephacryl S-300 gel filtration to be 50,000, 50,000-80,000, and 80,000, respectively. These GAGs were not digested with any glycosaminoglycanases. On the basis of one and two dimensional NMR spectra, glycosidase treatment and periodate oxidation of the pyridylaminated trisaccharide obtained by acid hydrolysis of illexin C, the unique repeating structure of the GAGs was determined to be (-6GalNAc alpha 1-3GlcA beta 1-3Fuc alpha 1-)n.

Amino Acids↗
PubMed1995

Neuronal specificity of subtype SQSC1 of squid putative sodium channel.

The distribution of SQSC1 mRNA in tissues of squid Loligo bleekeri was studied by the blot hybridization method. The complete cDNA for the coding region of SQSC1, the invertebrate putative sodium channel, was prepared from squid optic lobe (Sato and Matsumoto, Biochem. Biophys. Res. Comm. 186, 61-68, 1992). Transcriptional products of the SQSC1 gene were found to consist of two main different lengths (12 and 9 kb). The transcriptional products were detected in all the nervous tissues examined: optic lobes, cerebral ganglia and giant stellate ganglia. However, it was not detected in the muscle, suggesting the SQSC1 gene is specific for sodium channels of squid nerve cells. SQSC1 appears more widely distributed in the nervous system than GFLN1 which they reported as expressed specifically in stellate ganglion of the squid (Rosenthal and Gilly, Proc. Natl. Acad. Sci. USA 90, 10026-10030, 1993).

Alternative Splicing↗
PubMed1996

Ca2+ induces an increase in cGMP-phosphodiesterase activity in squid retinal photoreceptors.

In invertebrate photoreceptors, light elicits the opening of cationic channels to produce a depolarizing receptor potential. One hypothesis is that cGMP is the agent that gates the channels. It has been previously proposed that the light-induced rise in intracellular Ca2+ down-regulates phosphodiesterase activity, thereby eliciting an increase in intracellular cGMP concentration. cGMP-phosphodiesterase activity from squid photoreceptors was monitored both by a continuous fluorescence assay using 2'-o-(N-methylanthraniloyl)-cGMP and by hydrolysis of [3H]cGMP. The activity of cGMP-phosphodiesterase was found to be increased by Ca2+ in the physiological range of concentrations. These findings suggest that the previously known light-induced increase in Ca2+ in invertebrate photoreceptors cannot directly account for light-elicited down-regulation of cGMP-phosphodiesterase.

3',5'-Cyclic-GMP Phosphodiesterases↗
PubMed1996

Fatty acylation of synaptotagmin in PC12 cells and synaptosomes.

Synaptotagmin I is localized to synaptic vesicles where it functions in the calcium-triggered release of neurotransmitters. Here we demonstrate that synaptotagmin I covalently incorporated [3H]palmitate after metabolic labelling of PC-12 cells and rat brain synaptosomes. Labeling was localized to a tryptic fragment that contains a cluster of cysteine residues adjacent to the molecule's single transmembrane anchor. Neutral hydroxylamine released the [3H]palmitate from this fragment and increased its electrophoretic mobility, demonstrating that acylation occurs at the membrane-proximal cysteine cluster. In addition, hydroxylamine-induced mobility shifts were also apparent for synaptotagmins II and III, suggesting that posttranslational palmitoylation via thioester bonds may be a general modification of all synaptotagmins.

Acylation↗
PubMed1996

Illexins A, B, and C from squid ink should have a branched structure.

Illexin A, illexin B, and illexin C, isolated from ink of the squid Illex argentinus, have been reported to have a structure consisting of linear repeating units of (-6GalNAc alpha 1-3GlcA beta 1-3Fuc alpha 1-)n [Biochem. Biophys. Res. Commun. 198, 560 (1994)]. This structure was further investigated using NOESY and atmospheric pressure MS/MS measurement of PA-trisaccharide obtained by acid hydrolysis of illexin C. The results indicated that the structure is, in fact, branched. Observation of both [GalNAc-Fuc-PA]- and [GlcA-Fuc-PA]+ obtained as product ions from the molecular ion of PA-trisaccharide on the MS/ MS spectra suggested a branched repeating unit. NOEs between H-1 of GalNAc and H-3 of Fuc, and between H-1 of GlcA and H-4 of Fuc, revealed the positions of glycosidic linkages, and from the results of sodium periodate oxidation of illexin C and PA-trisaccharide, the structure was determined to be (-3GlcA beta 1-4(GalNAc alpha 1-3)Fuc alpha 1-)n.

Animals↗
PubMed1997

Molecular cloning and characterization of a putative neural calcium channel alpha1-subunit from squid optic lobe.

The complete amino acid sequence of a putative calcium channel alpha1-subunit, SQCC1, from the optic lobe of the squid Loligo bleekeri has been deduced by cloning and sequence analysis of the complementary DNA. The open reading frame encodes 2206 amino acids, which corresponds to a molecular weight of 251,451. The deduced amino acid sequence shares general structural features with the other voltage-dependent calcium channels; it consists of four repeated units of homology. Each motif has five hydrophobic segments and one positively charged segment. The transcriptional products were detected in all nervous systems examined; optic lobe, cerebral ganglia and giant stellate ganglia. However, it was not detected in the mantle muscle, heart and stomach, indicating SQCC1 is a calcium channel alpha1-subunit specific for squid nervous system. SQCC1 is more closely related in its amino acid sequence patterns to dihydropyridine-insensitive calcium channels rather than dihydropyridine-sensitive ones.

Amino Acid Sequence↗
PubMed2002

On the cable theory of nerve conduction.

Conduction of an impulse in the nonmyelinated nerve fiber is treated quantitatively by considering it as a direct consequence of the coexistence of two structurally distinct regions, resting and active, in the fiber. The profile of the electrical potential change induced in the vicinity of the boundary between the two regions is analyzed by using the cable equations. Simple mathematical formulae relating the conduction velocity to the electrical parameters of the fiber are derived from the symmetry of the potential profile at the boundary. The factors that determine the conduction velocity in the myelinated nerve fiber are reexamined.

Animals↗
PubMed1998

Primary peptide sequences from squid muscle and optic lobe myosin IIs: a strategy to identify an organelle myosin.

The squid giant axon provides an excellent model system for the study of actin-based organelle transport likely to be mediated by myosins, but the identification of these motors has proven to be difficult. Here the authors purified and obtained primary peptide sequence of squid muscle myosin as a first step in a strategy designed to identify myosins in the squid nervous system. Limited digestion yielded fourteen peptides derived from the muscle myosin which possess high amino acid sequence identities to myosin II from scallop (60-95%) and chick pectoralis muscle (31-83%). Antibodies generated to this purified muscle myosin were used to isolate a potential myosin from squid optic lobe which yielded 11 peptide fragments. Sequences from six of these fragments identified this protein as a myosin II. The other five sequences matched myosin II (50-60%, identities), and some also matched unconventional myosins (33-50%). A single band that has a molecular weight similar to the myosin purified from optic lobe copurifies with axoplasmic organelles, and, like the optic lobe myosin, this band is also recognized by the antibodies raised against squid muscle myosin II. Hence, this strategy provides an approach to the identification of a myosin associated with motile axoplasmic organelles.

Amino Acid Sequence↗
PubMed2000

Vibrio fischeri lipopolysaccharide induces developmental apoptosis, but not complete morphogenesis, of the Euprymna scolopes symbiotic light organ.

During initiation of the association between the squid host Euprymna scolopes and its bacterial partner Vibrio fischeri, the bacteria induce dramatic morphogenesis of the host symbiotic organ, a portion of which involves the signaling of widespread apoptosis of the cells in a superficial ciliated epithelium on the colonized organ. In this study, we investigated the role in this process of lipopolysaccharide (LPS), a bacterial cell-surface molecule implicated in the induction of animal cell apoptosis in other systems. Purified V. fischeri LPS, as well as the LPS of V. cholerae, Haemophilus influenzae, Escherichia coli, and Shigella flexneri, added in the concentration range of pg/ml to ng/ml, induced apoptosis in epithelial cells 10- to 100-fold above background levels. The absence of species specificity suggested that the conserved lipid A portion of the LPS was the responsible component of the LPS molecule. Lipid A from V. fischeri, E. coli, or S. flexneri induced apoptosis. In addition, strains of H. influenzae carrying a mutation in the htrB gene, which is involved in the synthesis of virulent lipid A, showed a diminished ability to induce apoptosis of host cells. Confocal microscopy using fluorescently labeled LPS indicated that the LPS behaves similar to intact bacterial symbionts, interacting with host cells in the internal crypt spaces and not directly with the superficial epithelium. Although LPS was able to induce apoptosis, it did not induce the full morphogenesis of the ciliated surface, suggesting that multiple signals are necessary to mediate the development of this animal-bacterial mutualism.

Animal Structures↗
PubMed1993

The encapsulation of squid diisopropylphosphorofluoridate-hydrolyzing enzyme within mouse erythrocytes.

This study describes the entrapment of squid-type diisopropylphosphorofluoridate-hydrolyzing enzyme (DFPase) within mouse red blood cells. These erythrocytes thereby gain the ability to rapidly hydrolyze alkylphosphate cholinesterase (ChE) inhibitors such as diisopropyl fluorophosphate (DFP). DFPase rapidly hydrolyzes DFP to diisopropyl phosphate. Resealed erythrocytes provide a stable carrier system that can preserve the activity of encapsulated enzymes against otherwise rapid in vivo degradation; thus, ChE inhibitors can be degraded to relatively nontoxic metabolites by these erythrocyte carriers. Squid DFPase was purified from the hepatopancreas of Atlantic squid and DFPase activity was determined by measuring changes in fluoride ion concentration using a fluoride ion selective electrode. Mouse erythrocytes in suspension with excess squid DFPase were dialyzed against hypotonic buffer to allow the encapsulation of the enzyme to occur. Cells were then resealed by returning the suspension to isosmotic with saline. Rate of DFP hydrolysis observed with these cells was much greater than the rate of nonenzymatic hydrolysis and was directly proportional to the amount of the erythrocyte suspension added to the assay solution. The rate of hydrolysis was first order in substrate. Erythrocyte controls showed no endogenous DFPase activity. These results suggest that enzyme entrapment may be developed as a method to prevent and antagonize organophosphate poisoning.

Animals↗
PubMed1994

X-ray diffraction study of the live squid retina.

In previous studies of invertebrate rhabdomes by X-ray diffraction, glutaraldehyde fixation of the retina was used because this tissue is very labile and, without fixation, disintegrates within an hour of dissection. However, with conventional X-ray apparatus more than ten hours exposure time was needed to record a diffraction pattern. In this study, X-ray diffraction patterns from unfixed squid retina could be successfully obtained by use of synchrotron radiation and a storage phosphor screen as detector. The diffraction spots were indexed on a two-dimensional hexagonal lattice of 60 nm. X-ray data was analysed by comparing Patterson functions calculated from the diffraction intensities with those based on model building. The hexagonal shape of microvillar cross section was suggested by the systematic weakness of (0, k) reflections beyond k = 4 and the appearance of the six symmetry-related diffuse maxima around (4 nm)-1. The best-fitting model showed a large gap between adjacent microvilli (approximately 12 nm), which has been expected (for ionic current flow through the inter-microvillus space to generate the membrane potential) but not observed with the chemically fixed retina, possibly due to an artifact of fixation. Also, the existence of massive inter-microvillus material, scarcely observed by conventional electron microscopy, has been confirmed.

Animals↗
PubMed1998

Interaction of monomeric and dimeric kinesin with microtubules.

The binding stoichiometry of kinesin to microtubules was determined using several biochemical and biophysical approaches (chemical crosslinking, binding assays, scanning transmission electron microscopy (STEM), image reconstruction, and X-ray scattering). The results show that each tubulin dimer associates with one kinesin head, irrespective of whether kinesin occurs in a monomeric or dimeric form in solution. Moreover, these heads appear to align along the protofilament axis generating a 16 nm periodicity of successive kinesin dimers. This is consistent with a "tightrope" model of movement where the first head of the dimer provides a guiding signal for the following one.

Animals↗