Keiichi Konoki - Academia.edu (original) (raw)

Papers by Keiichi Konoki

Marine Drugs, 2022

Saxitoxin and its analogues, paralytic shellfish toxins (PSTs), are potent and specific voltage-g... more Saxitoxin and its analogues, paralytic shellfish toxins (PSTs), are potent and specific voltage-gated sodium channel blockers. These toxins are produced by some species of freshwater cyanobacteria and marine dinoflagellates. We previously identified several biosynthetic intermediates of PSTs, as well as new analogues, from such organisms and proposed the biosynthetic and metabolic pathways of PSTs. In this study, 12β-deoxygonyautoxin 5 (12α-gonyautoxinol 5 = gonyautoxin 5-12(R)-ol) was identified in the freshwater cyanobacterium, Dolichospermum circinale (TA04), and 12β-deoxysaxitoxin (12α-saxitoxinol = saxitoxin-12(R)-ol) was identified in the same cyanobacterium and in the marine dinoflagellate Alexandrium pacificum (Group IV) (120518KureAC) for the first time from natural sources. The authentic standards of these compounds and 12α-deoxygonyautoxin 5 (12β-gonyautoxinol 5 = gonyautoxin 5-12(S)-ol) were prepared by chemical derivatization from the major PSTs, C1/C2, produced in D. c...

Proceedings of The National Academy of Sciences, 2010

Ca(V)1 channels initiate excitation-contraction coupling in skeletal and cardiac muscle. During t... more Ca(V)1 channels initiate excitation-contraction coupling in skeletal and cardiac muscle. During the fight-or-flight response, epinephrine released by the adrenal medulla and norepinephrine released from sympathetic nerves increase muscle contractility by activation of the β-adrenergic receptor/cAMP-dependent protein kinase pathway and up-regulation of Ca(V)1 channels in skeletal and cardiac muscle. Although the physiological mechanism of this pathway is well defined, the molecular mechanism and the sites of protein phosphorylation required for Ca(V)1 channel regulation are unknown. To identify the regulatory sites of phosphorylation under physiologically relevant conditions, Ca(V)1.1 channels were purified from skeletal muscle and sites of phosphorylation on the α1 subunit were identified by mass spectrometry. Two phosphorylation sites were identified in the proximal C-terminal domain, serine 1575 (S1575) and threonine 1579 (T1579), which are conserved in cardiac Ca(V)1.2 channels (S1700 and T1704, respectively). In vitro phosphorylation revealed that Ca(V)1.1-S1575 is a substrate for both cAMP-dependent protein kinase and calcium/calmodulin-dependent protein kinase II, whereas Ca(V)1.1-T1579 is a substrate for casein kinase 2. Treatment of rabbits with isoproterenol to activate β-adrenergic receptors increased phosphorylation of S1575 in skeletal muscle Ca(V)1.1 channels in vivo, and treatment with propranolol to inhibit β-adrenergic receptors reduced phosphorylation. As S1575 and T1579 in Ca(V)1.1 channels and their homologs in Ca(V)1.2 channels are located at a key regulatory interface between the distal and proximal C-terminal domains, it is likely that phosphorylation of these sites in skeletal and cardiac muscle is directly involved in calcium channel regulation in response to the sympathetic nervous system in the fight-or-flight response.

Toxicon, 2007

Voltage-gated sodium, calcium, and potassium channels generate electrical signals required for ac... more Voltage-gated sodium, calcium, and potassium channels generate electrical signals required for action potential generation and conduction and are the molecular targets for a broad range of potent neurotoxins. These channels are built on a common structural motif containing six transmembrane segments and a pore loop. Their pores are formed by the S5/S6 segments and the pore loop between them and are gated by bending of the S6 segments at a hinge glycine or proline residue. The voltage sensor domain consists of the S1 to S4 segments, with positively charged residues in the S4 segment serving as gating charges. The diversity of toxin action on these channels is illustrated by sodium channels, which are the molecular targets for toxins that act at five or more distinct receptor sites on the channel protein. Both hydrophilic low molecular weight toxins and larger polypeptide toxins physically block the pore and prevent sodium conductance. Hydrophobic alkaloid toxins and related lipid-soluble toxins act at intramembrane sites and alter voltage-dependent gating of sodium channels via an allosteric mechanism. In contrast, polypeptide toxins alter channel gating by voltage-sensor trapping through binding to extracellular receptor sites, and this toxin interaction has now been modeled at the atomic level for a -scorpion toxin. The voltage sensor trapping mechanism may be a common mode of action for polypeptide gating modifier β toxins acting on all of the voltage gated ion channels.

Proceedings of The National Academy of Sciences, 2005

In skeletal muscle cells, voltage-dependent potentiation of Ca 2؉ channel activity requires phosp... more In skeletal muscle cells, voltage-dependent potentiation of Ca 2؉ channel activity requires phosphorylation by cAMP-dependent protein kinase (PKA) anchored via an A-kinase anchoring protein (AKAP15), and the most rapid sites of phosphorylation are located in the C-terminal domain. Surprisingly, the site of interaction of the complex of PKA and AKAP15 with the ␣1-subunit of CaV1.1 channels lies in the distal C terminus, which is cleaved from the remainder of the channel by in vivo proteolytic processing. Here we report that the distal C terminus is noncovalently associated with the remainder of the channel via an interaction with a site in the proximal C-terminal domain when expressed as a separate protein in mammalian nonmuscle cells. Deletion mapping of the C terminus of the ␣1-subunit using the yeast two-hybrid assay revealed that a distal C-terminal peptide containing amino acids 1802-1841 specifically interacts with a region in the proximal C terminus containing amino acid residues 1556 -1612. Analysis of the purified ␣1-subunit of CaV1.1 channels from skeletal muscle by saturation sequencing of the intracellular peptides by tandem mass spectrometry identified the site of proteolytic processing as alanine 1664. Our results support the conclusion that a noncovalently associated complex of the ␣1-subunit truncated at A1664 with the proteolytically cleaved distal C-terminal domain, AKAP15, and PKA is the primary physiological form of CaV1.1 channels in skeletal muscle cells.

Proceedings of The National Academy of Sciences, 2005

In skeletal muscle cells, voltage-dependent potentiation of Ca2+ channel activity requires phosph... more In skeletal muscle cells, voltage-dependent potentiation of Ca2+ channel activity requires phosphorylation by cAMP-dependent protein kinase (PKA) anchored via an A-kinase anchoring protein (AKAP15), and the most rapid sites of phosphorylation are located in the C-terminal domain. Surprisingly, the site of interaction of the complex of PKA and AKAP15 with the 1-subunit of CaV1.1 channels lies in the distal C terminus, which is cleaved from the remainder of the channel by in vivo proteolytic processing. Here we report that the distal C terminus is noncovalently associated with the remainder of the channel via an interaction with a site in the proximal C-terminal domain when expressed as a separate protein in mammalian nonmuscle cells. Deletion mapping of the C terminus of the 1-subunit using the yeast two-hybrid assay revealed that a distal C-terminal peptide containing amino acids 1802-1841 specifically interacts with a region in the proximal C terminus containing amino acid residues 1556-1612. Analysis of the purified 1-subunit of CaV1.1 channels from skeletal muscle by saturation sequencing of the intracellular peptides by tandem mass spectrometry identified the site of proteolytic processing as alanine 1664. Our results support the conclusion that a noncovalently associated complex of the α1-subunit truncated at A1664 with the proteolytically cleaved distal C-terminal domain, AKAP15, and PKA is the primary physiological form of CaV1.1 channels in skeletal muscle cells.

Chemistry-a European Journal, 2009

The stereocontrolled total synthesis of the originally proposed (1) and correct (2) structures of... more The stereocontrolled total synthesis of the originally proposed (1) and correct (2) structures of (+)-neopeltolide, a novel marine macrolide natural product with highly potent antiproliferative activity against several cancer cell lines as well as potent antifungal activity, has been achieved by exploiting a newly developed Suzuki–Miyaura coupling/ring-closing metathesis strategy. Alkylborate 44, which was generated in situ from iodide 34, was coupled with enol phosphate 8 by a Suzuki–Miyaura coupling. Ring-closing metathesis of the derived diene 45 followed by stereoselective hydrogenation afforded tetrahydropyran 47 as a single stereoisomer in high overall yield from 34. Our convergent strategy enabled us to construct the 14-membered macrolactone core structure of 2 in a rapid and efficient manner. Total synthesis and biological evaluation of synthetic intermediates and designed synthetic analogues, performed to establish the structure–activity relationships of 2, led to the discovery of a structurally simple yet potent cytotoxic analogue, 9-demethylneopeltolide (54).

Journal of Medicinal Chemistry, 2009

3-(4-Fluorophenyl)-2-(4-pyridyl)chromone derivatives were synthesized and evaluated as p38 MAP ki... more 3-(4-Fluorophenyl)-2-(4-pyridyl)chromone derivatives were synthesized and evaluated as p38 MAP kinase inhibitors. Introduction of an amino group in the 2-position of the pyridyl moiety gave p38α inhibitors with IC 50 in the low nanomolar range (e.g., 8a, IC 50 = 17 nm). The inhibitors (8a and 8e) showed excellent selectivity profiles when tested on a panel of 62 kinases, as well as efficient inhibition (8e) of p38 signaling in human breast cancer cells.

Heterocycles, 2009

The photoactive and biotinylating ligand was prepared from MTX and maleimide-conjugated Hatanaka ... more The photoactive and biotinylating ligand was prepared from MTX and maleimide-conjugated Hatanaka reagent with use of Diels-Alder reaction. Blood cells were subjected to affinity labelling experiments using the ligand thus obtained. The labelled band on SDS-PAGE was replaced not by MTX but by brevetoxin B (PbTx2), which suggested the presence of binding proteins in blood cells. Screening of polyether compounds for MTX inhibitory activity using Ca 2+ flux assays in C6 cells disclosed that a synthetic fragment of the hydrophilic portion of MTX inhibited the MTX activity.

Forensic Toxicology, 2011

Recently, liquid chromatography–mass spectrometry (LC–MS) has been recognized as a useful method ... more Recently, liquid chromatography–mass spectrometry (LC–MS) has been recognized as a useful method to analyze tetrodotoxin (TTX), the primary toxin for puffer fish poisoning. TTX usually exists with its chemically interchangeable analogs, such as 4-epiTTX and 4, 9-anhydroTTX. TTX and 4-epiTTX have the same molecular weight and the same fragmentation pattern by tandem mass spectrometry (MS–MS). In this study, we optimized conditions for hydrophilic interaction liquid chromatography (HILC)–MS–MS to quantitate TTX, 4-epiTTX, 4,9-anhydroTTX, and 5,6,11-trideoxyTTX with good separation. The relationships between the applied amounts of each TTX analog to the HILC–MS–MS instrument and the peak areas showed good linearity in the ranges examined. The lower limits of detection (signal-to-noise ratio = 3) were 64 pg on-column for TTX, 128 pg for both 4-epiTTX and 4,9-anhydroTTX, and 180 pg for 5,6,11-trideoxyTTX using an API 2000 mass spectrometer.

Bioorganic & Medicinal Chemistry, 2009

The effect of phospholipid head group on the membrane-permeabilizing activity of amphotericin B (... more The effect of phospholipid head group on the membrane-permeabilizing activity of amphotericin B (AmB) was examined using 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) liposomes and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphatidylglycerol (POPG) liposomes. The activity of AmB was evaluated as K + influx measured as pH change inside liposomes by fluorescent measurements of 2 0 ,7 0 -bis(carboxyethyl)-4 or 5-carboxyfluorescein (BCECF). AmB showed prominent permeability in POPC liposomes, whereas hardly inducing ion flux in POPG membrane. POPC added to POPG liposomes as a minor constituent markedly enhanced membrane permeability, indicating the importance of a phosphonocholine group of PC for the drug's activity.

Bioorganic & Medicinal Chemistry Letters, 2008

Ladder-shaped polyether (LSP) compounds are thought to interact with transmembrane a-helices, but... more Ladder-shaped polyether (LSP) compounds are thought to interact with transmembrane a-helices, but direct evidence has scarcely obtained for these interactions. We adopted a transmembrane a-helix of glycophorin A, and quantitatively evaluated its interaction with LSPs such as yessotoxin (YTX), desulfated YTX and artificial LSPs, using surface plasmon resonance and saturation transfer difference NMR. As a result, dissociation constants (K D ) of YTX and desulfated YTX to a transmembrane domain peptide of glycophorin A were determined to be in the submillimolar range. Furthermore, in saturation transfer difference NMR, the signals at the polyene side chain and the angular methyl groups of YTX were significantly attenuated, which probably comprised an interacting interface of LSPs with a transmembrane a-helix.

Bioorganic & Medicinal Chemistry, 2010

Okadaic acid (OA) and dinophysistoxin-1 (DTX1) cause diarrheic shellfish poisoning. This article ... more Okadaic acid (OA) and dinophysistoxin-1 (DTX1) cause diarrheic shellfish poisoning. This article examines the biochemical interactions of the two toxins with novel okadaic acid binding proteins (OABPs) 2.1 and 2.3, originally isolated from the marine sponge Halichondria okadai. First, recombinant OABPs 2.1 and 2.3 were expressed in Escherichia coli BL21 (DE3) cells. Binding assays using [24-(3)H]OA and the recombinant OABP 2.1 or 2.3 demonstrated the dissociation constant K(d) of 1.30±0.56 nM and 1.54±0.35 nM, respectively. Binding of [24-(3)H]okadaic acid to recombinant OABP2.1 was almost equally replaced with OA and DTX1. OA-induced cytotoxicity in mouse leukemia P388 cells was inhibited in the presence of the recombinant OABPs 2.1 and 2.3 with an EC(50) of 92±8.4 nM and 87±13 nM, respectively. These results suggest that the blockage of OA-induced cytotoxicity by OABPs 2.1 and 2.3 may be involved in regulating symbiotic relationships present in the sponge H. okadai.

Chemical Research in Toxicology, 1999

Maitotoxin (MTX) at 0.3 nM elicited a 10-20-fold increase in the level of Ca 2+ influx in rat gli... more Maitotoxin (MTX) at 0.3 nM elicited a 10-20-fold increase in the level of Ca 2+ influx in rat glioma C6 cells. At higher doses (3-30 nM), MTX induced marked Ca 2+ influx in human erythrocyte ghosts when monitored with the fluorescent dye Fura-2. Although the ghosts were not as susceptible to MTX as intact erythrocytes or other cell lines, Fura-2 experiments under various conditions suggested that the MTX-induced entry of ions into the ghosts was mediated by a mechanism similar to that reported for cells or tissues. These ghosts are the simplest system known to be sensitive to MTX and thus may be suitable for research on the direct action of MTX. Gangliosides GM1 and GM3, glycosphingolipids which have a sialic acid residue, strongly inhibited MTX-induced Ca 2+ influx in C6 cells, while the inhibitory action by asialo-GM1, which lacks a sialic acid residue, was somewhat weaker. Their inhibitory potencies were in the following order: GM1 (IC 50 ∼ 2 µM) > GM3 (IC 50 ∼ 5 µM) > asialo-GM1 (IC 50 ∼ 20 µM). GM1 (3 µM) completely blocked MTX (30 nM)-induced Ca 2+ influx in human erythrocyte ghosts. When C6 cells were pretreated with tunicamycin, an antibiotic which inhibits N-linked glycosylation, or concanavalin A, a lectin which exhibits a high affinity for cell-surface oligosaccharides, MTX-induced Ca 2+ influx was significantly potentiated. This suggests that removal of oligosaccharides from the cell surface by tunicamycin or capping of sugar chains on plasma membranes by concanavalin A can potentiate the action of MTX. † Present address:

Bioorganic & Medicinal Chemistry Letters, 2010

Biochemistry, 2007

Okadaic acid, first isolated from the marine sponge Halichondria okadai, is a potent inhibitor of... more Okadaic acid, first isolated from the marine sponge Halichondria okadai, is a potent inhibitor of protein phosphatases 1 and 2A (PP1 and PP2A, respectively). Photoaffinity labeling experiments previously performed with biotinylated photoreactive okadaic acid revealed the presence of okadaic acid binding protein (OABP) in the crude extract of H. okadai. In this article, OABP1 and OABP2 were purified from H. okadai as guided by the binding affinity of [27-3H]okadaic acid. OABP1 has an approximate molecular mass of 37 kDa in SDS-PAGE analysis. Edman degradation followed by molecular cloning and sequencing identified OABP1 as being 88% identical to the rabbit PP2Abeta catalytic subunit. On the other hand, HPLC analysis revealed that OABP2 consists of three 22 kDa proteins (OABP2.1, OABP2.2, and OABP2.3). Electrospray ionization mass spectrometry indicated that OABP2.1 and OABP2.2 form a complex with okadaic acid. The complete amino acid sequence of OABP2, determined by Edman degradation and molecular cloning, showed that OABP2.1 is 96% identical to OABP2.2 and 66% identical to OABP2.3, while being very slightly homologous to any protein phosphatases known to date. OABP2 did not exhibit phosphatase activity, though it bound to okadaic acid with a Kd of 0.97 nM. Furthermore, OABP2 was not detected in the sponge Halichondria japonica or the dinoflagellate Prorocentrum lima. We thus speculated that OABP2 might be involved in detoxifying okadaic acid.

Bioorganic & Medicinal Chemistry, 2011

Advanced glycation end products (AGE) are known to cause diabetes complications in hyperglycemia ... more Advanced glycation end products (AGE) are known to cause diabetes complications in hyperglycemia patients. In this study we prepared hetero-trimers of collagen model peptides comprising Ac-(Pro-Hyp-Gly) 5 -Pro-Lys-Gly-(Pro-Hyp-Gly) 5 -Ala-NH 2 (4) and Ac-(Pro-Hyp-Gly) 11 -Ala-NH 2 (5) to investigate the clustering effect of lysine on AGE formation. The formation rate of carboxymethyllysine over several months was determined for the mixtures of peptides 4 and 5 at (3:0), (2:1) and (1:2) in the presence of glucose. The contents of carboxymethyllysine were significantly enhanced for (3:0) and (2:1) as compared with (1:2), suggesting that the proximity of lysine residues in the trimers accelerated formation of the AGE. Furthermore, a lysine dimerization moiety (GOLD) was identified for the first time from AGEs of glucose origin, which implied the significance of GOLD in oligomerization of collagens and other longlife proteins.

Organic Letters, 2008

Combinatorial synthesis of a 1,5-polyol system corresponding to the C1-C14 unit of amphidinol 3 (... more Combinatorial synthesis of a 1,5-polyol system corresponding to the C1-C14 unit of amphidinol 3 (AM3) and its diastereomers was achieved via chemoselective cross metathesis as the key step. Comparison of 13 C NMR data of the synthetic specimens with that of AM3 led to a controversy regarding the originally proposed structure. From GC-MS analysis of the degradation product, the absolute configuration at C2 of AM3 has been revised to be R.

Journal of The American Chemical Society, 2008

Ladder-shaped polyether (LSP) toxins represented by brevetoxins and ciguatoxins are thought to bi... more Ladder-shaped polyether (LSP) toxins represented by brevetoxins and ciguatoxins are thought to bind to transmembrane (TM) proteins. To elucidate the interactions of LSPs with TM proteins, we have synthesized artificial ladder-shaped polyethers (ALPs) containing 6/7/6/6 tetracyclic, 6/7/6/6/7/6/6 heptacyclic, and 6/7/6/6/7/6/6/7/6/6 decacyclic systems, based on the convergent method via R-cyano ethers. The ALPs possessing the simple iterative structure with different numbers of rings would be useful for structure-activity relationship studies on the molecular length, which is supposed to be important when naturally occurring LSPs elicit their toxicity. Two series of ALPs were prepared to evaluate the hydrophilic or hydrophobic effects of the side chains: (i) both sides were functionalized as diols (A series), and (ii) one side remained as diol and the other side was protected as benzyl ethers (B series). To examine the interaction of these ALPs with TM proteins, dissociation of glycophorin A (GpA) dimers into monomers was evaluated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The heptacyclic ether (ALP7B) elicited the most potent activity in the presence of 2% SDS buffer, whereas the decacyclic ether (ALP10A) exhibited an intriguing phenomenon to induce precipitation of GpA in a dose-dependent manner, under the low concentration of SDS (0.03%). ALP10A also induced precipitation of integrin R 1 1, a TM protein known to form heterodimers in the lipid bilayer membranes. The different activities among the ALPs can be accounted for by the concept of "hydrophobic matching" that is, lengths of the hydrophobic region including the side chains of ALP7B and ALP10A are ca. 25 Å, which match the lengths of the hydrophobic region of R-helical TM proteins, as well as the hydrophobic thickness of lipid bilayer membranes. The concept of the hydrophobic matching would be a clue to understanding the interaction between LSPs and TM proteins, and also a guiding principle to design ALPs possessing potent affinities with TM proteins. (3) (a) Shimizu, Y.; Chou, H.-N.; Bando, H.; Van Duyne, G.; Clardy, J. C. J. Am. Chem. Soc. 1986, 108, 514-515. (b) Pawlak, J.; Tempesta, M. S.; Golik, J.; Zagorski, M. G.; Lee, M. S.; Nakanishi, K.; Iwashita, T.; Gross, M. L.; Tomer, K. B.

Tetrahedron, 2000

AbstractÐFour biotin conjugates of okadaic acid were synthesized for evaluating their interaction... more AbstractÐFour biotin conjugates of okadaic acid were synthesized for evaluating their interactions with protein phosphatase 2A (PP2A) by surface plasmon resonance (SPR). C7-biotinylated okadaic acid exhibited the strongest binding af®nity to the enzyme, while C1-biotinylated derivative was devoid of af®nity. C24-or C27-biotinylated okadaic acid showed moderate af®nity to the enzyme. In the wake of this ®nding, a biotinyl photoaf®nity probe was introduced into 7-OH of okadaic acid. Photoaf®nity labeling followed by SDS-PAGE analysis indicated that the okadaic acid derivative clearly labeled PP2A. Furthermore, three proteins were also labeled in crude extracts of a marine sponge Halichondria okadai. All these results imply that the C7-biotin conjugate is a versatile reagent for biochemical studies of okadaic acidbinding proteins including PP2A. q

Marine Drugs, 2022

Proceedings of The National Academy of Sciences, 2010

Toxicon, 2007

Proceedings of The National Academy of Sciences, 2005

Chemistry-a European Journal, 2009

Journal of Medicinal Chemistry, 2009

Heterocycles, 2009

Forensic Toxicology, 2011

Bioorganic & Medicinal Chemistry, 2009

Bioorganic & Medicinal Chemistry Letters, 2008

Bioorganic & Medicinal Chemistry, 2010

Chemical Research in Toxicology, 1999

Bioorganic & Medicinal Chemistry Letters, 2010

Biochemistry, 2007

Bioorganic & Medicinal Chemistry, 2011

Organic Letters, 2008

Journal of The American Chemical Society, 2008

Tetrahedron, 2000