Biomedical subjects

O Shouno

Publications and source records attributed to O Shouno.

5 recordsLinked to original sources

PubMed1999

Characterization of N-acylation of Go alpha purified from bovine retinas.

Heterogeneous N-terminal acylation has been identified in several retinal proteins localized predominantly in the outer segments of the photoreceptor cells, but it is still unclear whether such a unique heteroacylation is determined by a photoreceptor cell-specific factor or not. Here, we characterized the N-terminal modification of bovine retinal Go alpha, which seems to be involved in the neural activities and is not detected in the photoreceptor outer segments. In the proteolytic fragments of immunoaffinity-purified retinal Go alpha, we found a single N-terminal peptide modified with myristate, and concluded that retinal Go alpha is purely myristoylated, just like brain Go alpha. This result indicates that the heteroacylation has a more restricted origin in the retina, and supports the idea that it is a photoreceptor cell-specific modification.

Acylation↗

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↗

PubMed1997

NADPH-diaphorase containing cells and fibers in the central nervous system of squid, Loligo bleekeri keferstein.

Distribution of NADPH-diaphorase in the central nervous system of squid was determined using histochemical technique. We found NADPH-diaphorase positive cell bodies and fibers both in the optic and the posterior anterior lobe and fibers in the peduncle lobe. These results clarify the biochemical similarity between two structurally similar organs of invertebrate and vertebrate, the peduncle lobe and the anterior basal lobe, and the cerebellum. NADPH-diaphorase positive fibers innervated the inner granule layer and the outer plexiform layer of the outer cortex of the optic lobe. This is in good agreement with avian centrifugal projection from isthmo-optic nucleus to retina where nitric oxide synthase is known to be contained. There may be at least two distinct neural systems, the motor control system and the visual information processing system, which use nitric oxide as a transmitter or modulator in the squid central nervous system.

Animals↗

PubMed1996

Preparation and characterization of monoclonal antibodies specific for lauroylated isoform of bovine transducin alpha-subunit: immunohistochemical analysis of bovine retinas.

The photoreceptor G protein transducin [alpha- and beta gamma-subunits (T alpha/T beta gamma)] plays a central role in the visual transduction process. The amino-terminus of bovine T alpha is modified by one of four distinct fatty acids-laurate (C12:0), myristate (C14:0), C14:1 (5-cis), and C14:2 (5-cis, 8-cis)-but the biological significance and the localization of the four isoforms of T alpha are poorly understood. To investigate the cellular distribution of each isoform, we prepared monoclonal antibodies against a synthetic C12:0-, C14:0-, C14:1-, or C14:2-nonapeptide corresponding to the N-terminal region of T alpha. Among several types of antibodies isolated, only one type, represented by LA4, reacted specifically with the C12:0-peptide as well as purified T alpha but not with the other proteins in bovine retinal homogenate, including recoverin, indicating that the epitope comprises both C12:0 and the N-terminal amino acids of T alpha. Immunohistochemical analyses of bovine retinal sections by LA4 showed the uniform distribution of C12:0-T alpha in almost all the rod outer segments. Hence, it seemed unlikely that each isoform of T alpha was localized in specific cells. This observation, together with evidence for a possible functional diversity among the isoforms, suggests that the four isoforms of T alpha in a single rod cell may contribute simultaneously to a fine tuning of the photon-signal transduction process.

Acylation↗

PubMed1996

[Channel structure and functioning based on octagonal structure model].

On the basis of the sequence comparison of squid sodium channel SQSCl with those of other channels, we have proposed a tertiary structure model of the sodium channel where the transmembrane segments are octagonally aligned and the four linkers of S5-6 between segments S5 and S6 play a crucial role in the activation gate, voltage sensor and ion selective pore, which can slide, depending on membrane potentials, along inner walls consisting of segments S2 and S4 alternately. The proposed octagonal structure model is contrasted with that of Noda et al (Nature 320 : 188-192, 1986) and with Durrel and Guy (Biophys J 62 : 238-250, 1992). The octagonal structure model can explain the gating of activation and inactivation, the ion selectivity, and as well, the action mechanism of both tetrodotoxin (TTX) and a-scorpion toxin (ScTX), and be applied not only to the sodium channel, but also to the calcium channel, potassium channel, cGMP gated channel and further to the inwardly rectifying K channels. However Yan and Horn have discussed voltage dependent S4 movement in sodium channels from the accessibility of methanethiosulfonate (MTSET) to cystein residue which was substituted for the outermost arginine in IVS4 (Neuron 15 : 213-218, 1995), the neutralization of the arginine was revealed not to influence the activation of the channel. It suggest that the residue in the 3rd position of IVS4 is not a part of the voltage sensor located in the membrane. These result suggest that the change of the accessibility might be caused by the change of the covering of the residue rather than the movement of S4.

Amino Acid Sequence↗