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PubMed2000

Arginine kinase from Nautilus pompilius, a living fossil. Site-directed mutagenesis studies on the role of amino acid residues in the Guanidino specificity region.

Arginine kinases were isolated from the cephalopods Nautilus pompilius, Octopus vulgaris, and Sepioteuthis lessoniana, and the cDNA-derived amino acid sequences have been determined. Although the origin and evolution of cephalopods have long been obscure, this work provides the first molecular evidence for the phylogenetic position of Cephalopoda in molluscan evolution. A crystal structure for Limulus arginine kinase showed that four amino acid residues (Ser(63), Gly(64), Val(65), and Tyr(68)) are hydrogen-bonded with the substrate arginine. We introduced three independent mutations, Ser(63) --> Gly, Ser(63) --> Thr, and Tyr(68) --> Ser, in Nautilus arginine kinase. One of the mutants had a considerably reduced substrate affinity, accompanied by a decreased V(max). In other mutants, the activity was lost almost completely. It is known that substantial conformational changes take place upon substrate binding in arginine kinase. We hypothesize that the hydrogen bond between Asp(62) and Arg(193) stabilizes the closed, substrate-bound state. Site-directed mutagenesis studies strongly support this hypothesis. The mutant (Asp(62) --> Gly or Arg(193) --> Gly), which destabilizes the maintenance of the closed state and/or perhaps disrupts the unique topology of the catalytic pocket, showed only a very weak activity (0.6-1.5% to the wild-type).

Amino Acid Sequence↗
PubMed2004

S-crystallin and arginine kinase bind F-actin in light- and dark-adapted octopus retinas.

PURPOSE: Rhabdomere microvilli dramatically reorganize in conditions of light and dark. This reorganization involves remodeling of the microvillus actin cytoskeleton. We are using the rhabdomeric retina of Octopus bimaculoides to identify actin-binding proteins that may be involved in this remodeling. METHODS: Octopus were light-/dark-adapted, retinas separated into dorsal and ventral halves, and homogenized. Actin-binding proteins were recognized using F-actin overlay blot assays and selected proteins from the overlays were identified using N-terminal sequencing methods or mass spectroscopy. Protein concentrations were quantified and compared by statistical analysis. RESULTS: Total protein gels of light-/dark-adapted, ventral/dorsal halves were almost identical except for a protein band at 26 kD. The relative amount of this protein in the dark was almost double that found in the light. The levels of other proteins did not vary significantly between the light and dark. F-actin overlays also showed matching patterns of actin-binding proteins except for the 26 kD protein. Although the 26 kD protein from light-adapted retinas transferred to the blotting membranes, it did not bind F-actin while the 26 kD protein on overlays from dark-adapted retinas always demonstrated F-actin binding. Besides the 26 kD protein, other proteins at 200 kD, 80 kD, 40 kD appeared on the overlays. These proteins and the 26 kD protein were sequenced and identified as hemocynanin, transitional ER ATPase, arginine kinase and S-crystallin, respectively. CONCLUSIONS: The amount of S-crystallin present in the octopus retina is significantly greater in dark-adapted retinas and it binds to F-actin. In the light, the level of S-crystallin is greatly reduced and there is no apparent F-actin binding. No other studies, to our knowledge, show that S-crystallin binds to the actin cytoskeleton or that its expression is regulated by light. Arginine kinase may provide energy for cytoskeletal remodeling as it may in other neural tissues.

Actins↗
PubMed2002

Chromatin condensation, cysteine-rich protamine, and establishment of disulphide interprotamine bonds during spermiogenesis of Eledone cirrhosa (Cephalopoda).

During spermiogenesis in Eledone cirrhosa a single protamine substitutes for histones in nuclei of developing spermatids. This protein displays a peculiar primary structure. It contains 22.6 mol% cysteine residues (19 cysteines in 84 residues). This makes it the most cysteine-rich protamine known. The proportion of basic residues is relatively low (arginine 36.9 mol%, lysine 19.0 mol%). The protamine of E. cirrhosa condenses spermiogenic chromatin in a pattern which comprises fibres with a progressively larger diameter and lamellae that finally undergo definitive coalescence. We have also performed a study that estimates the number of interprotamine disulphide bonds formed during the process of spermiogenic chromatin condensation by means of sequential disappearance of MMNA (monomaleimido-nanogold) labelling. During the first step of spermiogenesis, protamines are found spread over very slightly condensed chromatin with their cysteines in a reactive state (protamine-cys-SH). From this stage the interprotamine disulphide bonds are established in a progressive way. First they are formed inside the chromatin fibres. Subsequently, they participate in the mechanism of fibre coalescence and finally, in the last step of spermiogenesis, the remaining free reactive -SH groups of cysteine form disulphide bonds, thus promoting a definitive stabilization of the nucleoprotein complex in the ripe sperm nucleus.

Amino Acid Sequence↗
PubMed2004

Content of mercury and cadmium in fish (Thunnus alalunga) and cephalopods (Eledone moschata) from the south-eastern Mediterranean Sea.

Mercury and cadmium concentrations were measured in the flesh and liver (or hepatopancreas) of albacore (Thunnus alalunga) and horned octopus (Eledone moschata) to establish whether the concentrations exceeded the maximum levels fixed by the European Commission. In both species, mercury and cadmium mean concentrations were higher in liver (albacore: mercury = 2.41 microg g(-1) wet wt, cadmium = 9.22 microg g(-1) wet wt; horned octopus: mercury = 0.76 microg g(-1) wet wt, cadmium = 6.72 microg g(-1) wet wt) than in flesh (albacore: mercury = 1.56 microg g(-1) wet wt, cadmium = 0.05 microg g(-1) wet wt; horned octopus: mercury = 0.36 microg g(-1) wet wt, cadmium = 0.33 microg g(-1)). Mercury concentrations exceeding the prescribed legal limit of 1 microg g(-1) wet wt were found in almost all albacore samples (flesh: 71.4%; liver: 85.7%). For horned octopus, concentrations above 0.5 microg g(-1) wet wt were observed solely in hepatopancreas, while in flesh, the concentrations were below this limit in all the samples examined. Of the flesh samples of albacore, 42.8% exceeded the proposed tolerance for cadmium for human consumption, whilst for horned octopus, the established limit was not exceeded in any sample.

Animals↗
PubMed1999

Cadmium and total mercury in some cephalopods from the South Adriatic Sea (Italy).

In the framework of a wide monitoring programme on the presence of heavy metals in marine organisms caught in the South Adriatic Sea, cadmium and total mercury concentrations were determined in flesh and hepatopancreas of 512 specimens of two species of cephalopods. The aim of the study was to establish the quality of the marine food with respect to the health of consumers and to investigate cadmium and mercury distribution in organisms representing different habitats. For both elements, higher levels were found in spider octopus (Octopus salutii) than in broadtail squid (Illex coindeti). Between the two different tissues analysed, higher concentrations were observed in hepatopancreas than flesh. According to the rules in force, no flesh sample showed cadmium and total mercury concentrations exceeding the peak permitted values of 2 mg/kg wet wt and 0.5 mg/kg wet wt respectively.

Animals↗
PubMed2004

A cysteine-activated protease isolated from Todarodes pacificus squid degrades collagen below its denaturation temperature.

Collagen purified from the mantle muscle of the Japanese common squid, Todarodes pacificus, showed autodegradation during incubation under acidic conditions at 25 degrees C, without the addition of exogenous enzymes. This suggests that the collagenolytic proteases bind to collagen tightly through the steps of collagen preparation. Collagenolytic activity also was detected in a crude extract of mantle muscle, and leupeptin and E-64 were observed to inhibit collagenolytic activity within the collagen fraction and muscle extract. We purified these collagenolytic cysteine proteases by leupeptin column chromatography and cellulose acetate membrane electrophoresis. Optimal enzymatic activity was observed at pH 3.5, and collagenolytic activity was completely suppressed at neutral or alkaline pH. The purified enzymes were 28 kDa and 25 kDa in size, and both had gelatinolytic activity, as detected by gelatin zymography, and cut the specific site of denatured collagen alpha chain. The purified enzymes degraded squid collagen at 25 degrees C, which is 2.5 degrees lower than the temperature at which squid collagen normally denatures; however, the proteases were ineffective at 20 degrees C. Interestingly, the isolated proteases were capable of digesting both squid and bovine gelatin. In this article, we describe collagenolytic cysteine proteases that bind to the collagen of Todarodes pacificus, thereby digesting it by attacking microunfolding regions generated by incubation 2-3 degrees C below the denaturation temperature.

Amino Acid Sequence↗
PubMed1964

ELECTRON MICROSCOPY OF SYNAPTIC STRUCTURE OF OCTOPUS BRAIN.

The well known type of synapse between a presynaptic process containing vesicles and a "clear" postsynaptic process can be commonly observed in the various lobes of the brain of Octopus. The presynaptic vesicles are aggregated near regions of the synaptic membranes which show specialisation and asymmetric "thickening" indicating functional polarisation, and here chemical transmission is presumed to take place. In addition, in the vertical lobe a very interesting serial arrangement of synaptic contacts occurs. Presynaptic bags, formed from varicosities of fibres from the superior frontal lobe, contact the trunks of amacrine cells in the manner just described. The trunks, however, although apparently postsynaptic are themselves packed with synaptic vesicles. The trunks, in turn, make "presynaptic" contacts with clear spinous processes of other neurons of yet undetermined origin. Typical polarised membrane specialisations occur at the contact regions. The trunk vesicles aggregated closest to the contact regions have a shell of particles round their walls. At present, there is no way of telling whether the membrane conductance to the various ions is differently affected at either of the transmission sites, and, if an inhibitory mechanism is involved, whether it is of the presynaptic or postsynaptic variety.

Animals↗
PubMed1965

FINE STRUCTURE OF THE OCTOPUS RETINA.

The fine structure of the visual and the supporting cells and of the blood capillaries in the octopus retina is described. Lamellated structures contained in the proximal segment of the visual cell consist of compact arrays of dense membranes each of which is quintuple-layered and divides at its margins into two thinner sheets or membranes which are connected directly with the agranular or granular endoplasmic reticulum. Proximal to the deeper extremities of the rhabdomeres, the lateral plasma membranes of two adjoining visual cells contact each other forming a quintuple-layered compound membrane, which results in occlusion of the intercellular space. The central layer of the compound membrane is of high density, so that the membrane, as a whole, appears to be a single thick layer at low magnifications. The supporting cells are connected with the neighboring visual cells by two types of junctions. Long slender processes extend from the supporting cells to the surface of the retina through narrow spaces among the distal segments of the visual cells. The capillary endothelial cells are characterized by luminal surfaces irregularly contoured and by lateral surfaces elaborately interdigitated. The functional significance of the close contact between adjoining visual cells is discussed.

Animals↗
PubMed1960

The fine structure of some retinal photoreceptors.

An electron microscope study has been made of octopus and amphibian photoreceptors, after fixing with KMnO(4) and embedding in araldite. What has previously been seen as a single dense stratum bounding the tubular compartments (octopus) or the double membrane discs (rods and cones), now shows a double structure. We interpret this as showing that these tubules and discs have similar bounding surfaces, which are probably directly related to the cell membrane. This is confirmed by the finding that the tubules and discs are (at least occasionally) continuous with the cell membrane.

Animals↗
PubMed1996

The low-frequency dielectric properties of octopus arm muscle measured in vivo.

The conductance and capacitance of octopus arm are measured in vivo over the frequency range 5 Hz to 1 MHz. Measurement of these parameters for a number of electrode separations permits the determination of the variations in tissue conductivity and dielectric constant with frequency. In the range 1-100 kHz the conductivity is independent of the frequency f and the dielectric constant varies as f-1. These results, in conjunction with those reported previously for frog skeletal muscle, are consistent with the fractal model for the dielectric properties of animal tissue proposed by Dissado. Transformation of the results to complex impedance spectra indicates the presence of a dispersion above 100 kHz.

Animals↗
PubMed1997

A novel monoantennary complex-type sugar chain found in octopus rhodopsin: occurrence of the Gal beta1-->4Fuc group linked to the proximal N-acetylglucosamine residue of the trimannosyl core.

The N-linked sugar chains were liberated as oligosaccharides from octopus rhodopsin by hydrazinolysis. Most of the oligosaccharides were neutral, and separated into two major components by column chromatography using immobilized lectins and Bio-Gel P-4. Structural analysis of the one major component by sequential exoglycosidase digestion, chemical fragmentation in combination with methylation analysis revealed that it is a nonasaccharide; Man alpha1-->6(Gal beta1-->3GlcNAc beta1-->2Man alpha1-->3)Man beta1--> 4GlcNAc beta1-->4(Gal beta1-->4Fuc alpha1-->6)GlcNAc. This structure is quite unique in that a novel galactosylated fucose residue is attached to the reducing terminal N-acetylglucosamine residue.

Acetylglucosamine↗
PubMed1984

Evolution of multicellular animals as deduced from 5S rRNA sequences: a possible early emergence of the Mesozoa.

The nucleotide sequences of 5S rRNA from a mesozoan Dicyema misakiense and three metazoan species, i.e., an acorn-worm Saccoglossus kowalevskii, a moss-animal Bugula neritina, and an octopus Octopus vulgaris have been determined. A phylogenic tree of multicellular animals has been constructed from 73 5S rRNA sequences available at present including those from the above four sequences. The tree suggests that the mesozoan is the most ancient multicellular animal identified so far, its emergence time being almost the same as that of flagellated or ciliated protozoans. The branching points of planarians and nematodes are a little later than that of the mesozoan but are clearly earlier than other metazoan groups including sponges and jellyfishes. Many metazoan groups seem to have diverged within a relatively short period.

Animals↗
PubMed1996

Kinetic characterization of the endogenous glutathione transferase activity of octopus lens S-crystallin.

The kinetic mechanism of the endogenous glutathione transferase (GST) activity of octopus S-crystallin was investigated by steady-state kinetics. Biphasic double-reciprocal plots were obtained for both glutathione and the hydrophobic substrate 1-chloro-2,4-dinitrobenzene (CDNB). Substrate inhibition was observed only for CDNB with Ksi value of 29.7 +/- 0.01 mM. The catalytic constant for S-crystallin was three orders of magnitude smaller than that for the digestive gland GST of the same species. The initial-velocity studies indicated that the enzyme reaction might conform to a steady-state random Bi-Bi kinetic mechanism, being similar to the reaction of GST from other sources. The pH-rate profiles also suggest that the same chemical mechanism for the nucleophilic aromatic substitution between GSH and CDNB was employed for S-crystallin. The interaction of Tyr7 with the bound GSH lowered the pKa value of the sulfhydryl group of GSH to 6.82-6.85, which is 2.32-2.35 pH unit smaller than that found in aqueous solution. This lowering of pKa value produces the thiolate anion of GSH, a better nucleophile to attack the ipso carbon of CDNB, resulting in formation of Meisenheimer complex intermediate. Removing the chloride ion from this intermediate complex produces the conjugate product. Using the method devised by Wang and Srivastava (Anal. Biochem. 216, 15-26, 1994), the functional unit of the dimeric S-crystallin was estimated to be a monomer. The possible biological implications of the endogenous detoxification ability of cephalopods S-crystallin are discussed.

Animals↗
PubMed1991

Total synthesis of a gene for octopus rhodopsin and its preliminary expression.

To carry out systematic structure-function studies of octopus rhodopsin, photoreceptor protein of octopus visual cells, by means of specific amino-acid replacements, we have totally synthesized a DNA duplex of 1,365 base pairs that encodes the entire octopus rhodopsin of 455 amino acids [Ovchinnikov et al. (1988) FEBS Lett. 232, 69-72] by introducing codons preferred in Escherichia coli. Total synthesis simplifies site-specific mutagenesis in all parts of the gene by replacement of short restriction fragments by their newly synthesized counterparts containing the required nucleotide alterations. Thirty unique restriction sites were introduced in the octopus rhodopsin gene, which was assembled on a plasmid in two steps. Five cartridge genes of 344, 296, 320, 212, and 317 base pairs capable of being expressed independently were first constructed by using 48 synthetic oligonucleotides ranging in size from 54 to 73 nucleotides. The entire gene was constructed by consecutive linkage of cartridge genes. These cartridge genes were designed to correspond to the transmembrane helical unit of octopus rhodopsin, resulting in easy construction of various chimeric rhodopsins. The nucleotide sequences were confirmed by sequencing the cartridges as well as the entire gene. These synthetic genes were cloned into an expression vector carrying the trp promoter of E. coli, and were preliminarily expressed in vitro and in vivo.

Amino Acid Sequence↗
PubMed1994

Expression of octopus rhodopsin in Escherichia coli.

Apoproteins, having various molecular weights, of octopus rhodopsin (oRh, 455 amino acids), which is a typical transmembrane protein, were expressed in Escherichia coli with an inducible expression system using promoter phi 10 of the T7 phage. Fifteen synthetic genes (212-1,365 bp) for oRh (1) were cloned downstream from gene 10 of the T7 phage (846 bp), under the control of promoter phi 10. An expression vector for mature oRh containing no extra peptide resulting from gene 10 was also constructed. Protein productivities were mainly evaluated by ELISA using monoclonal antibodies. The expression level in E. coli of the fused oRh genes varied between 1 and 200 mg/liter of the culture medium (from approximately 0.25 to 50% of the total cell protein, respectively), depending on the fused oRh genes. The amount of mature oRh protein expressed in E. coli was approximately 0.1 to 1 mg/liter. Hydropathy index analysis of gene products showed a significant negative correlation (rho = - 0.63) between expression level of oRh gene products in E. coli and their hydrophobic characteristics. Wavelength shifting of the absorption maximum by exogenous addition of retinal to apoprotein similar to that of authentic oRh was demonstrated in the membrane fraction of E. coli expressing mature opsin.

Animals↗