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At least 523 records · Page 29Linked to original sources
PubMed1993

Cloning and nucleotide sequence of cDNA for rhodopsin of the squid Todarodes pacificus.

A cDNA for rhodopsin was isolated from a library constructed from poly(A)+RNA of the squid (Todarodes pacificus) retina. One positive clone with the longest insert of cDNA (3.1 kb) was selected by employing a PCR-amplified cDNA fragment as a probe. The nucleotide sequence of the cDNA revealed a single open reading frame of 1,344 bp encoding a polypeptide (M(r)49,833), which covered a complete sequence for the squid opsin. This clone had a very long 3'-non-coding region (1.7 kb) including multiple polyadenylation signals, AATAAA, resembling the clones for Todarodes retinochrome and retinal-binding protein (RALBP). The analysis of hydropathicity demonstrated the presence of seven transmembrane spanning domains, and a possible retinal-binding site, Lys-305, was found in the 7th domain. Todarodes rhodopsin contained characteristic sequences of PPQGY repeated in the C-terminal region, as reported in Loligo and octopus rhodopsins. Structural comparison of those cephalopod rhodopsins is also discussed.

Amino Acid Sequence↗
PubMed1995

Effect of the C-terminal proline repeats on ordered packing of squid rhodopsin and its mobility in membranes.

Negative stain electron microscopy and saturation transfer electron spin resonance spectroscopy have been used to compare the lattice ordering and in-plane membrane mobility of full-length and C-terminally cleaved squid rhodopsin. The C-terminus of squid rhodopsin contains a negatively charged region followed by 9-10 repeats of a proline-rich sequence, not found in rhodopsins other than those of cephalopod invertebrates, but similar proline repeats are found in other, unrelated membrane proteins. We find that the proline repeats cluster the rhodopsins into small groups, interfering with two-dimensional crystallization and maintaining their mobility in the membrane.

Animals↗
PubMed1994

Small GTP-binding proteins of squid photoreceptor. Interaction with photoactivated rhodopsin.

Squid photoreceptor membranes contain several small GTP-binding proteins (22-27 kDa) in addition to heterotrimeric G-proteins. In addition, these membranes contain several proteins which can be ADP-ribosylated by exoenzyme C3 from Clostridium botulinum (C3). These proteins are similar but not identical to C3 substrates from bovine rod outer segments. It is shown that substrates of C3 in squid photoreceptor interact with rhodopsin in a light-dependent manner. These data suggest involvement of small GTP-binding proteins in phototransduction processes in invertebrates.

ADP Ribose Transferases↗
PubMed1995

The sequence of a cytoplasmic intermediate filament (IF) protein from the annelid Lumbricus terrestris emphasizes a distinctive feature of protostomic IF proteins.

The complete cDNA clone for a cytoplasmic intermediate filament (IF) protein from the annelid Lumbricus terrestris reported here, shows an extra 42 residues in the coil 1b subdomain of the central rod, as do the IF proteins from nematodes and molluscs. These extra six heptads are also present in all nuclear lamins but not in any known vertebrate cytoplasmic IF protein. Thus, it seems that protostomic metazoa conserve a lamin-like structural element in their cytoplasmic IF proteins, which was lost in the deuterostomic metazoan branch leading to the vertebrates.

Animals↗
PubMed1995

A beta-subclass phosphatidylinositol-specific phospholipase C from squid (Loligo forbesi) photoreceptors exhibiting a truncated C-terminus.

A PCR-based strategy has been used to isolate a full length cDNA encoding a phosphatidylinositol-specific phospholipase C from a sized cDNA squid (Loligo forbesi) retinal library. The predicted protein sequence contains 875 amino acids, with calculated M(r) 98,181, and has marked similarity with PLC beta-isoforms, including conservation of the 'X' and 'Y' regions. It is unique in having a major C-terminal truncation. A major protein of apparent M(r) 120,000 estimated by SDS-PAGE has been isolated from squid photoreceptors and identified by partial protein sequence analysis to correspond to the protein sequence predicted from the cDNA clone. This protein has been shown to hydrolyse phosphatidylinositol 4,5-bisphosphate. It is not yet clear whether this represents the major light-activated PLC in squid vision.

Amino Acid Sequence↗
PubMed1995

Squid photoreceptor phospholipase C is stimulated by membrane Gq alpha but not by soluble Gq alpha.

Phospholipase C (PLC) was purified from squid retina. Soluble Gq alpha, membrane Gq alpha and G beta gamma were isolated from GTP gamma S-treated and light-illuminated photoreceptor membranes. The membrane Gq alpha stimulated phosphatidyl inositol-phospholipase C (PI-PLC) activity in a dose-dependent manner. Soluble Gq alpha and membrane G beta gamma showed no stimulating effects on PLC. GTP gamma S-binding was found exclusively in membrane fraction, with very little present in the KCl-soluble fraction which contained soluble Gq alpha. These results indicate that light-activated rhodopsin activates PLC through membrane-bound Gq alpha and suggest that the rhodopsin/Gq/PLC cascade might be the pathway of phototransduction in squid photoreceptors.

Animals↗
PubMed1991

Isolation and chemical study of the glycosaminoglycans from squid cornea.

1. Oversulphated chondroitin sulphate (ca 93% of tissue glycosaminoglycans) with average molecular weight 72,500, chondroitin sulphate (5%) and small amounts of lowsulphated chondroitin sulphate were isolated from squid cornea. 2. The sulphation pattern of oversulphated chondroitin sulphate was delta di-4S (52%), delta di-diSD (28%), delta di-6S (9%) and delta di-OSCS (11%) and that of chondroitin sulphate 49, 1, 20 and 30% respectively. 3. All glycosaminoglycans contained neutral monosaccharides, glucose being the predominant neutral monosaccharide in oversulphated chondroitin sulphate and chondroitin sulphate and fucose in low-sulphated chondroitin sulphate. 4. Although L-iduronic acid was not detected, the digestion of oversulphated chondroitin sulphate with chondroitinases ABC and AC gave unexpected results.

Animals↗
PubMed1995

Determination of hyaluronan and galactosaminoglycan disaccharides by high-performance capillary electrophoresis at the attomole level. Applications to analyses of tissue and cell culture proteoglycans.

A rapid, highly sensitive and reproducible HPCE method is described for the determination of all non- and variously sulphated disaccharides present in hyaluronan and vertebrate chondroitin sulphates and dermatan sulphates. Following chondroitinase digestion of glycosaminoglycans or proteoglycans, the non-, di- and tri-sulphated delta-disaccharides are completely separated and readily determined within 14 min on a fused-silica capillary in 15 mM sodium dihydrogen orthophosphate, pH 3.00, using reversed polarity at 20 kV and detection at 232 nm. The determination of the various delta-disaccharides derived from either glucuronic or iduronic acid and the presence of glucuronic and iduronic clustered structures in dermatan sulphate can also easily be made, using digests with chondroitinase AC or B. A linear detector response was obtained for the entire interval tested (up to 10 mg/l of delta-disaccharides). Concentrations as small as 32, 65, 100 and 250 pmol/l (22, 38, 50 and 98 ng/l) of tri-, di- and nonsulphated delta-disaccharides, respectively, can be reliably detected.

Animals↗
PubMed1987

X-ray diffraction patterns from microtubules and neurofilaments in axoplasm.

Freshly extracted axoplasm from giant axons of the marine fan worm Myxicola infundibulum and the squid Loligo can be pulled into fibres that contain highly oriented cytoskeletal elements suitable for X-ray diffraction. A major advantage of studying axoplasmic components by this technique is that it allows essentially native structures and their interactions to be examined. We describe here the analyses of the X-ray diffraction patterns. We show that in Myxicola the pattern can be explained by diffraction from both neurofilaments and microtubules, whilst in Loligo the pattern arises solely from microtubules. At low resolution, X-ray patterns obtained from dehydrated axoplasmic microtubules resemble strongly the Fourier transforms generated from electron micrographs of negatively stained specimens. Hydration of axoplasmic fibres produced reversible changes in the X-ray pattern intensities, although the layer-line positions were unaltered. On the 4 nm layer-line, the intensity of the J3 reflection was dramatically reduced on hydration, though its position was unchanged. Hydration also affected the J10/J16 reflections, which increased in intensity, though here again the positions of the peaks were little altered. The X-ray patterns from our hydrated fibres resemble those produced by others from fibres of purified microtubules, though in our patterns contrast is generated towards the centre of the wall. We interpret our findings in the light of current ideas about microtubule structure as determined by X-ray diffraction and electron microscope techniques.

Animals↗