Importance of N-terminal regions of G protein alpha subunits for the activation of phospholipase C in Xenopus oocytes

The alpha subunits of Gq family G proteins, GL1 alpha and GL2 alpha, are bovine homologues of mouse G14 alpha and G11 alpha, respectively, and are closely related to each other. When expressed in Xenopus oocytes together with metabotropic glutamate receptors, GL2 alpha activates endogenous phospholipase C (PLCx) in response to glutamate stimulation, whereas GL1 alpha inhibits the activation of PLCx. By examining the properties of 10 chimeras between GL1 alpha and GL2 alpha and their mutants, we tried to identify the regions on the G alpha proteins that are important for the activation of PLCx. The results indicated that a necessary (but not sufficient) condition for a chimeric G alpha protein to be able to clearly activate PLCx was that its N-terminal quarter portion should be derived from GL2 alpha. No correlation was found between the origin (GL1 alpha or GL2 alpha) of C-terminal regions of the chimeras and the ability of chimeras to activate PLCx. One of the chimeras is different from GL2 alpha at only four amino acid residues in the N-terminal region, and yet it could not activate PLCx. When one of the four residues, Ser-59, in the chimera was mutated back to Ala as in the original GL2 alpha, the resulting mutant became capable of activating PLCx. This residue is localized in the midst of the N-terminal linker connecting the two major domains in the G alpha proteins. These results indicate that Ala-59 is critical for the activation of PLCx, and that the linker may play important roles in determining functions of G alpha proteins.

Structure and regional distribution of nociceptin/orphanin FQ precursor

We have cloned cDNA carrying the entire coding sequence of the precursor protein for nociceptin/orphanin FQ, a neuropeptide-ligand for an opioid-receptor like G-protein coupled receptor. The deduced nociceptin/orphanin FQ precursor shows sequence similarity to the opioid peptide precursors and shares characteristic structural features particularly with preprodynorphin. In situ hybridization analysis of nociceptin precursor mRNA in the mouse central nervous system revealed that it is highly expressed in discrete neuronal sites with the pattern distinct from those of opioid peptides.

Effect of transcranial Doppler intensity on successful recording in Japanese patients

The major limitation of transcranial Doppler sonography (TCD) is the failure to obtain data for all patients. The purpose of this study was to determine in detail the effect of increasing ultrasonic acoustic intensity on the rate of successful recording of intracranial blood velocity signals. The study was performed in 239 Japanese patients using a 2-MHz range-gated, pulsed-wave TCD. The middle cerebral artery flow signals were recorded at 76, 152, 228, 304, 380, 456 and 532 mW/cm2 and the results analyzed by age, gender and intensity. The rate of successful recording showed significant increase with the ultrasonic intensity in both genders (45.7% at 76 mW/cm2 vs. 81.1% at 532 mW/cm2 in males and 29.5% vs. 60.7% in females). However, recording was only successful in 54% of aged (50-89 gamma) female patients at the highest ultrasonic intensity used. It should be possible to significantly increase TCD usefulness in an aging Japanese population by further increasing TCD acoustic intensity within safety limitation.

Synthesis of a glycopeptide carrying a N-linked core pentasaccharide

A glycopeptide carrying a pentasaccharide core structure of asparagine-linked glycoproteins was synthesized. The synthesis of the carbohydrate part was performed starting from monosaccharide components in an unambiguous manner. The resultant pentaglycosyl azide was reduced into corresponding glycosyl amine and coupled with an aspartic acid derivative to furnish an Asn-linked oligosaccharide in a protected form. Subsequent coupling with a dipeptide, followed by deprotection gave the target compound.

Characterization of Gq family G proteins GL1 alpha (G14 alpha), GL2 alpha (G11 alpha), and Gq alpha expressed in the baculovirus-insect cell system

The alpha subunits of Gq family G proteins, GL1 alpha (G14 alpha), GL2 alpha(G11 alpha), and Gq alpha were expressed with G protein beta 1 and gamma 2 subunits in insect cells using a baculovirus system. The trimeric forms of G proteins, GL1 (GL1 alpha beta gamma), GL2 (GL2 alpha beta gamma), and Gq (Gq alpha beta gamma), were solubilized by 1% sodium cholate and purified by sequential chromatography on three kinds of columns. GL1, GL2, and Gq activated phospholipase C-beta purified from bovine brain in the presence of aluminum fluoride to the same extent. Muscarinic acetylcholine receptor m1 subtype stimulated the guanosine 5'-O-(3-thiotriphosphate) (GTP gamma S) binding to GL1, GL2, and Gq in the presence of similar concentrations of carbamylcholine. When m1 receptor, G protein, and phospholipase C-beta were reconstituted in lipid vesicles, each subtype of Gq family G proteins mediated the activation of phospholipase C-beta by carbamylcholine in the presence of either 1 microM GTP gamma S or 1 mM GTP. Phospholipase C-beta stimulated the GTPase activity of GL1, GL2, and Gq in the presence of m1 receptor and carbamylcholine but did not stimulate the GTPase activity of GO. Protein kinase C phosphorylated m1 receptor and phospholipase C-beta, but the phosphorylation did not significantly affect the ability of the m1 receptor to stimulate phospholipase C-beta in the reconstitution system of purified proteins.

A region of the muscarinic-gated atrial K+ channel critical for activation by G protein beta gamma subunits

Complementary DNAs encoding two types of inwardly rectifying K+ channels, GIRK1 and IRK1, have been cloned from rat atrium and mouse macrophage, respectively. GIRK1 expressed in Xenopus oocytes was activated by acetylcholine when m2 muscarinic acetylcholine receptor was coexpressed. The acetylcholine-induced activation of GIRK1 was enhanced by coexpression with the G protein beta 1 gamma 2 subunit but not the beta 1 gamma 1 or alpha subunits. Deletion of the C-terminus of GIRK1 impaired the channel activation associated with the beta 1 gamma 2 subunit. Moreover, replacement of the C-terminus of IRK1 with that of GIRK1 produced a chimera channel that was activated by the beta 1 gamma 2 subunit, whereas intact IRK1 was not activated by the beta 1 gamma 2 subunit. These findings define the C-terminus of GIRK1 as a regulatory region for the G protein beta gamma subunit.

Tyrosine kinases Lyn and Syk regulate B cell receptor-coupled Ca2+ mobilization through distinct pathways

Stimulation of B lymphocytes through their antigen receptor (BCR) results in rapid increases in tyrosine phosphorylation on a number of proteins and induces both an increase of phosphatidylinositol and mobilization of cytoplasmic free calcium. The BCR associates with two classes of tyrosine kinase: Src-family kinase (Lyn, Fyn, Blk or Lck) and Syk kinase. To dissect the functional roles of these two types of kinase in BCR signaling, lyn-negative and syk-negative B cell lines were established. Syk-deficient B cells abolished the tyrosine phosphorylation of phospholipase C-gamma 2, resulting in the loss of both inositol 1,4,5-trisphosphate (IP3) generation and calcium mobilization upon receptor stimulation. Crosslinking of BCR on Lyn-deficient cells evoked a delayed and slow Ca2+ mobilization, despite the normal kinetics of IP3 turnover. These results demonstrate that Syk mediates IP3 generation, whereas Lyn regulates Ca2+ mobilization through a process independent of IP3 generation.

G protein-mediated inhibition of phosphoinositide metabolism evoked by metabotropic glutamate receptors in frog oocytes

1. Metabotropic glutamate receptor subtype 1 (mGluR1), when expressed in Xenopus oocytes, activates phosphoinositide-specific phospholipase C (PLC) in a G protein-dependent manner. This reaction results in the activation of chloride channels in the oocytes, and can be monitored electrophysiologically. We expressed different G protein alpha-subunits together with mGluR1 in oocytes, and examined the effects of these G protein subunits on the PLC-mediated reaction. 2. The expression of the alpha-subunit of GL2, a bovine version of G11, which is a member of the Gq subgroup, potentiated the mGluR1-evoked reaction, whereas the alpha-subunit of GL1, a bovine G14, which is also a member of the Gq subgroup, strongly suppressed it. The expression of Gs alpha also suppressed this reaction. 3. We then expressed G beta 1 gamma 2-subunits in addition to the G alpha-subunits, and examined the mGluR1-evoked reactions. Both the potentiation and suppression by GL2 alpha and GL1 alpha, respectively, were more pronounced in the presence of the G beta 1 gamma 2-subunits. In contrast, the suppression by Gs alpha was completely reversed by G beta 1 gamma 2. 4. The direct activation of G proteins by the intracellular injection of either fluoride ions or guanosine-5'-O-(3-thiotriphosphate) (GTP gamma S) causes similar PLC-mediated reactions. The expression of GL2 alpha, GL1 alpha or Gs alpha caused potentiation, suppression and no change, respectively, on the fluoride- (or GTP gamma S-) evoked reactions.(ABSTRACT TRUNCATED AT 250 WORDS)

[Platelet accumulation in abdominal aortic aneurysms and the effect of antiplatelet drugs: assessment by indium platelet scintigraphy]

A dual tracer technique using 111In labeled platelets and 99mTc labeled human serum albumin was applied to evaluate the in vivo thrombogenicity in 12 cases with abdominal aortic aneurysm (AAA) and the effect of antiplatelet drug on the thrombogenicity. The magnitude of platelet accumulation at AAA was expressed as the ratio of radioactivity of 111In platelets on the vascular wall to those in the blood pool (PAI; platelet accumulation index). Of the 12 patients with AAA, 11 had positive studies on baseline imaging and 1 had equivocally positive image. The PAI value (Mean +/- SD) over the AAA was 53.8 +/- 34.1% as compared to -8.6 +/- 4.4% in the control group (p less than 0.01). Seven patients with an AAA and positive baseline images were restudied during platelet active drug with 325 mg of aspirin. During treatment with aspirin, of 7 patients, 5 had positive images, of which 3 were decreased and others unchanged compared to baseline studies, 1 equivocally positive one and one negative one. The PAI value during treatment (21.9 +/- 18.6%) was significantly decreased compared to those in baseline study (52.1 +/- 23.9%). Our results suggest that the method used for platelet imaging in the present study may be useful for studying the in vivo thrombogenicity and the effect of platelet active drugs in AAA.

Synthesis of an octasaccharide fragment of high-mannose-type glycans of glycoproteins

O-(alpha-D-Mannopyranosyl)-(1----2)-O-(alpha-D-mannopyranosyl)-(1----3)- O- [(alpha-D-mannopyranosyl)-(1----2)-O-(alpha-D-mannopyranosyl)-(1----6)]- O- (alpha-D-mannopyranosyl)-(1----6)-O-(beta-D-mannopyranosyl)-(1----4)-O-( 2- acetamido-2-deoxy-beta-D-glucopyranosyl)-(1----4)-2-acetamido-2-deoxy- glucopyranose, an octasaccharide fragment of high-mannose type glycan of glycoproteins, was synthesized. Crucial glycosylation of trisaccharide intermediate, benzyl O-(2,4-di-O-benzyl-beta-D-mannopyranosyl)-(1----4)-O-(2-acetamido-3,6-di -O- benzyl-2-deoxy-beta-D-glucopyranosyl)-(1----4)-2-acetamido-3,6-di-O-benz yl-2- deoxy-beta-D-glucopyranoside, was successful only with a di-O-acetyltetradeca-O-benzyl-D-mannopentaosyl chloride. The use of the corresponding hexadeca-O-acetyl-D-mannopentaosyl bromide did not give the desired product.

[Assessment of the rate of successful transcranial Doppler recording through the temporal windows in Japanese with special reference to aging and sex]

Transcranial Doppler method (TCD), newly developed in 1982, is ultrasound technology that measures physiologic parameters of blood flow in the major intracranial arteries. A major limitation of TCD is that, in some individuals, satisfactory recording is not possible, especially through the temporal windows. The purpose of the present study is to assess the rate of successful recording in TCD through the temporal ultrasonic windows in Japanese with special reference to aging and sex. In 423 Japanese (244 males and 179 females) aged from 25 to 93 years, measurement of blood flow velocity in basal cerebral arteries was performed by transcranial Doppler velocimeter with a 2 MHz pulsed wave Doppler probe. The signal was successfully recorded in 299 of 423 Japanese (71%). In Japanese males, successful measurement was more frequent (206/244; 84%) than in Japanese females (93/179; 52%). The rate of successful recording was evaluated in every decade from the twenties to the eighties, and it was found to decrease significantly according to age (100%, 94%, 91%, 74%, 66%, 67%, and 46%, respectively). In females, it significantly decreased in those older than 50 years old (100%, 100%, 93%, 61%, 36% 43%, and 27%, respectively), but not in males (100%, 88%, 89%, 81%, 88%, 83%, and 69%, respectively). These findings suggest that this noninvasive method has clinical usefulness for evaluating intracranial circulation but has limitation for assessing the intracranial lesions of elderly Japanese women.

Identification of two novel GTP-binding protein alpha-subunits that lack apparent ADP-ribosylation sites for pertussis toxin

Molecular cloning of cDNAs encoding alpha-subunits of guanine nucleotide-binding regulatory proteins (G-proteins) has revealed the existence of nine species of alpha-subunits. We have identified two additional G-protein alpha-subunits, which we refer to as GL1 alpha and GL2 alpha, by isolating bovine liver cDNA clones that cross-hybridized at reduced stringency with bovine Gi1 alpha-subunit cDNA. The deduced amino acid sequences of GL1 alpha and GL2 alpha share 83% identity with each other and show 45-55% identity with those of other known G-protein alpha-subunits. Both GL1 alpha and GL2 alpha lack a consensus site for ADP-ribosylation by pertussis toxin. Messenger RNA corresponding to GL2 alpha was detected in all tissues examined, but GL1 alpha mRNA was detected only in liver, lung, and kidney. Antiserum prepared against a synthetic pentadecapeptide corresponding to the deduced carboxyl terminus of GL2 alpha specifically reacted with a 40-kDa protein in mouse liver, brain, lung, heart, kidney, and spleen. The amount of the 40-kDa protein was highest in brain and lung. We suggest that GL1 alpha and GL2 alpha are new members of a subfamily of pertussis toxin-insensitive G-proteins.

Conformation of the glucotriose unit in the lipid-linked oligosaccharide precursor for protein glycosylation

The conformation of the glucotriose unit of the protein glycosylation precursor Glc3Man9GlcNAc2 was assessed by deuterium exchange studies on the model tetrasaccharide alpha Glc----2 alpha Glc----3 alpha Glc----3 alpha Man----OCH2CH2CH3 dissolved in deuterated dimethyl sulfoxide. The hydroxyl proton on C-2 of the nonreducing end glucose and on C-4 of the glucose attached to mannose both show dramatic isotope shifts indicative of a strong hydrogen bond between these two hydroxyl groups. Such a hydrogen bond requires a fixed conformation of the glucotriose unit that brings these hydroxyl groups within 3 A of each other, a conformation that is supported by molecular modeling based on hard-sphere exo-anomeric (HSEA) calculations. The temperature dependence of the hydroxyl proton chemical shifts supports the postulated hydrogen bond, and the torsional angles between the three glucose units derived from the HSEA calculations are consistent with results from related studies on other saccharides. The results support a model for biochemical function in which the glucotriose unit could modulate the activity of the oligosaccharyltransferase by binding in a fixed conformation to a specific effector site in the enzyme.

Synthesis of alpha-D-Manp-(1----3)-[beta-D-GlcpNAc-(1----4)]-[alpha-D-Manp+ ++-(1----6)] - beta-D-Manp-(1----4)-beta-D-GlcpNAc-(1----4)-[alpha-L-Fucp- (1----6)]-D- GlcpNAc, a core glycoheptaose of a "bisected" complex-type glycan of glycoproteins

A synthesis of alpha-D-Manp-(1----3)-[beta-D-GlcpNAc-(1----4)]-[alpha-D-Manp++ +-(1----6)]- beta-D-Manp-(1----4)-beta-D-GlcpNAc-(1----4)-[alpha-L-Fucp-( 1----6)]-D- GlcpNAc was achieved by employing benzyl O-(3,4,6-tri-O-benzyl-2-deoxy-2-phthalimido-beta-D-glucopyranosyl)-(1--- -4)-O- (2-O-benzyl-beta-D-mannopyranosyl)-(1----4)-O-(3,6-di-O-benzyl-2-deoxy-2 - phthalimido-beta-D-glucopyranosyl)-(1----4)-3-O-benzyl-2-deoxy-6-O-p- methoxyphenyl-2-phthalimido-beta-D-glucopyranoside as a key glycosyl acceptor. Highly stereoselective mannosylation was performed by taking advantage of the 2-O-acetyl group in the mannosyl donors. The alpha-L-fucopyranosyl residue was also stereoselectively introduced by copper(II)-mediated activation of methyl 2,3,4-tri-O-benzyl-1-thio-beta-L-fucopyranoside.

Synthesis of an appropriately protected core glycotetraoside, a key intermediate for the synthesis of "bisected" complex-type glycans of a glycoprotein

A stereocontrolled synthetic route to a glycotetraoside, allyl O-(3,4,6-tri-O-benzyl-2-deoxy-2-phthalimido-beta-D-glucopyranosyl)-(1--- -4)-O- (3,6-di-O-allyl-2-O-benzyl-beta-D-mannopyranosyl)-(1----4)-O-3, 6-di-O-benzyl-2-deoxy-2-phthalimido-beta-D-glucopyranosyl)-(1----4)-3-O- benzyl- 2-deoxy-6-O-p-methoxy-phenyl-2-phthalimido-beta-D-glucopyranoside, an important intermediate for the synthesis of "bisected" complex type glycans of glycoproteins has been established by employing two glycosyl donors, 3,4,6-tri-O-benzyl-2-deoxy-2-phthalimido-beta-D-glucopyranosyl trichloroacetimidate and 4-O-acetyl-3,6-di-O-allyl-2-O-benzyl-alpha-D-mannopyranosyl bromide, and a glycosyl acceptor, allyl O-(3,6-di-O-benzyl-2-deoxy-2-phthalimido-beta-D-glucopyranosyl)-(1----4) -3-O- benzyl-2-deoxy-6-O-p-methoxyphenyl-2-phthalimido-beta-D-glucopyranoside.

[Assessment of reproducibility of transcranial Doppler velocimetry]

In recent years, transcranial Doppler velocimetry has been widely used as a noninvasive method for measurement of blood flow velocity in basal cerebral arteries. As for the reproducibility of this method, however, there have been only few reports so far. In the present study, we attempted to evaluate the reproducibility of this method by changing the examiners and the timing of the examination. Fifteen healthy volunteers were investigated by using a pulsed wave Doppler ultrasound device with a 2 MHz transducer. Both peak and mean spatial frequencies calculated from the frequency spectrum of the Doppler signals from the middle cerebral artery (MCA) and the basilar artery (BA) were used as blood flow parameters for assessing the reproducibility. The arterial blood pressure and the end-tidal carbon dioxide partial pressure (PECO2) were also monitored during the ultrasonic examinations. The intra- and inter-observer reproducibilities were evaluated by obtaining the coefficient of variation (CV) of the differences and/or analyzing the correlation between the values from the two measurements by the same examiner and by two separate examiners, respectively. The intraobserver reproducibility in separate days was also evaluated. Both in the mean arterial blood pressure and in PECO2, no significant changes were observed between the two measurements in each subjects. In the present examination, the CV and r values ranged from 6.7 to 19.5% and from 0.69 to 0.95, respectively, showing good reproducibility of the transcranial Doppler method for measurement of blood flow velocity, though some differences were observed as follows. The intraobserver reproducibility was better than the interobserver reproducibility.(ABSTRACT TRUNCATED AT 250 WORDS)

Total synthesis of X hapten, III3 Fuc alpha-nLc4 Cer

Total synthesis of O-beta-D-galactopyranosyl-(1----4)-O-[alpha-L- fucopyranosyl- (1----3)]-O-(2-acetamido-2-deoxy-beta-D-glucopyranosyl)-(1----3)-O-beta- D- galactopyranosyl- (1----4)-O-beta-D-glucopyranosyl-(1----1)-2-N-tetracosanoyl-(2S,3R ,4E)- sphingenine was achieved by use of the key glycosyl donors O-(2,3,4,6-tetra-O-acetyl-beta-D- galactopyranosyl)-(1----4)-O-[(2,3,4-tri-O-acetyl-alpha-L-fucopyranosyl) - (1----3)]-O-(2- acetamido-6-O-acetyl-2-deoxy-beta-D-glucopyranosyl)-(1----3)-O-(2,4,6-tr i-O- acetyl- beta-D-galactopyranosyl)-(1----4)-2,3,6-tri-O-acetyl-alpha-D-glucopyrano syl trichloroacetimidate and fluoride, as well as key glycosyl acceptor 3-O-benzoyl-2-N-tetracosanoyl- (2S,3R,4E)-sphingenine, in an unambiguous manner.