1
|
Monastyrnaya MM, Kalina RS, Kozlovskaya EP. The Sea Anemone Neurotoxins Modulating Sodium Channels: An Insight at Structure and Functional Activity after Four Decades of Investigation. Toxins (Basel) 2022; 15:toxins15010008. [PMID: 36668828 PMCID: PMC9863223 DOI: 10.3390/toxins15010008] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2022] [Revised: 12/13/2022] [Accepted: 12/15/2022] [Indexed: 12/24/2022] Open
Abstract
Many human cardiovascular and neurological disorders (such as ischemia, epileptic seizures, traumatic brain injury, neuropathic pain, etc.) are associated with the abnormal functional activity of voltage-gated sodium channels (VGSCs/NaVs). Many natural toxins, including the sea anemone toxins (called neurotoxins), are an indispensable and promising tool in pharmacological researches. They have widely been carried out over the past three decades, in particular, in establishing different NaV subtypes functional properties and a specific role in various pathologies. Therefore, a large number of publications are currently dedicated to the search and study of the structure-functional relationships of new sea anemone natural neurotoxins-potential pharmacologically active compounds that specifically interact with various subtypes of voltage gated sodium channels as drug discovery targets. This review presents and summarizes some updated data on the structure-functional relationships of known sea anemone neurotoxins belonging to four structural types. The review also emphasizes the study of type 2 neurotoxins, produced by the tropical sea anemone Heteractis crispa, five structurally homologous and one unique double-stranded peptide that, due to the absence of a functionally significant Arg14 residue, loses toxicity but retains the ability to modulate several VGSCs subtypes.
Collapse
|
2
|
Xiao Y, Blumenthal K, Cummins TR. Gating-pore currents demonstrate selective and specific modulation of individual sodium channel voltage-sensors by biological toxins. Mol Pharmacol 2014; 86:159-67. [PMID: 24898004 DOI: 10.1124/mol.114.092338] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Voltage-gated sodium channels are critical determinants of nerve and muscle excitability. Although numerous toxins and small molecules target sodium channels, identifying the mechanisms of action is challenging. Here we used gating-pore currents selectively generated in each of the voltage-sensors from the four α-subunit domains (DI-DIV) to monitor the activity of individual voltage-sensors and to investigate the molecular determinants of sodium channel pharmacology. The tarantula toxin huwentoxin-IV (HWTX-IV), which inhibits sodium channel current, exclusively enhanced inward gating-pore currents through the DII voltage-sensor. By contrast, the tarantula toxin ProTx-II, which also inhibits sodium channel currents, altered the gating-pore currents in multiple voltage-sensors in a complex manner. Thus, whereas HWTX-IV inhibits central-pore currents by selectively trapping the DII voltage-sensor in the resting configuration, ProTx-II seems to inhibit central-pore currents by differentially altering the configuration of multiple voltage-sensors. The sea anemone toxin anthopleurin B, which impairs open-channel inactivation, exclusively enhanced inward gating-pore currents through the DIV voltage-sensor. This indicates that trapping the DIV voltage-sensor in the resting configuration selectively impairs open-channel inactivation. Furthermore, these data indicate that although activation of all four voltage-sensors is not required for central-pore current generation, activation of the DII voltage-sensor is crucial. Overall, our data demonstrate that gating-pore currents can determine the mechanism of action for sodium channel gating modifiers with high precision. We propose this approach could be adapted to identify the molecular mechanisms of action for gating modifiers of various voltage-gated ion channels.
Collapse
Affiliation(s)
- Yucheng Xiao
- Department of Pharmacology and Toxicology, Indiana University School of Medicine, Indianapolis, Indiana (Y.X., T.R.C.); Department of Biochemistry, School of Medicine and Biomedical Sciences, State University of New York, Buffalo, New York (K.B.)
| | - Kenneth Blumenthal
- Department of Pharmacology and Toxicology, Indiana University School of Medicine, Indianapolis, Indiana (Y.X., T.R.C.); Department of Biochemistry, School of Medicine and Biomedical Sciences, State University of New York, Buffalo, New York (K.B.)
| | - Theodore R Cummins
- Department of Pharmacology and Toxicology, Indiana University School of Medicine, Indianapolis, Indiana (Y.X., T.R.C.); Department of Biochemistry, School of Medicine and Biomedical Sciences, State University of New York, Buffalo, New York (K.B.)
| |
Collapse
|
3
|
AdE-1, a new inotropic Na+ channel toxin from Aiptasia diaphana, is similar to, yet distinct from, known anemone Na+ channel toxins. Biochem J 2013; 451:81-90. [DOI: 10.1042/bj20121623] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Heart failure is one of the most prevalent causes of death in the western world. Sea anemone contains a myriad of short peptide neurotoxins affecting many pharmacological targets, several of which possess cardiotonic activity. In the present study we describe the isolation and characterization of AdE-1 (ion channel modifier), a novel cardiotonic peptide from the sea anemone Aiptasia diaphana, which differs from other cnidarian toxins. Although AdE-1 has the same cysteine residue arrangement as sea anemone type 1 and 2 Na+ channel toxins, its sequence contains many substitutions in conserved and essential sites and its overall homology to other toxins identified to date is low (<36%). Physiologically, AdE-1 increases the amplitude of cardiomyocyte contraction and slows the late phase of the twitch relaxation velocity with no induction of spontaneous twitching. It increases action potential duration of cardiomyocytes with no effect on its threshold and on the cell's resting potential. Similar to other sea anemone Na+ channel toxins such as Av2 (Anemonia viridis toxin II), AdE-1 markedly inhibits Na+ current inactivation with no significant effect on current activation, suggesting a similar mechanism of action. However, its effects on twitch relaxation velocity, action potential amplitude and on the time to peak suggest that this novel toxin affects cardiomyocyte function via a more complex mechanism. Additionally, Av2's characteristic delayed and early after-depolarizations were not observed. Despite its structural differences, AdE-1 physiologic effectiveness is comparable with Av2 with a similar ED50 value to blowfly larvae. This finding raises questions regarding the extent of the universality of structure–function in sea anemone Na+ channel toxins.
Collapse
|
4
|
Chang SC, Galea CA, Leung EWW, Tajhya RB, Beeton C, Pennington MW, Norton RS. Expression and isotopic labelling of the potassium channel blocker ShK toxin as a thioredoxin fusion protein in bacteria. Toxicon 2012; 60:840-50. [PMID: 22659540 DOI: 10.1016/j.toxicon.2012.05.017] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2012] [Revised: 05/21/2012] [Accepted: 05/23/2012] [Indexed: 01/02/2023]
Abstract
The polypeptide toxin ShK is a potent blocker of Kv1.3 potassium channels, which play a crucial role in the activation of human effector memory T-cells (T(EM)). Selective blockers constitute valuable therapeutic leads for the treatment of autoimmune diseases mediated by T(EM) cells, such as multiple sclerosis, rheumatoid arthritis, and type-1 diabetes. We have established a recombinant peptide expression system in order to generate isotopically-labelled ShK and various ShK analogues for in-depth biophysical and pharmacological studies. ShK was expressed as a thioredoxin fusion protein in Escherichia coli BL21 (DE3) cells and purified initially by Ni²⁺ iminodiacetic acid affinity chromatography. The fusion protein was cleaved with enterokinase and purified to homogeneity by reverse-phase HPLC. NMR spectra of ¹⁵N-labelled ShK were similar to those reported previously for the unlabelled synthetic peptide, confirming that recombinant ShK was correctly folded. Recombinant ShK blocked Kv1.3 channels with a K(d) of 25 pM and inhibited the proliferation of human and rat T lymphocytes with a preference for T(EM) cells, with similar potency to synthetic ShK in all assays. This expression system also enables the efficient production of ¹⁵N-labelled ShK for NMR studies of peptide dynamics and of the interaction of ShK with Kv1.3 channels.
Collapse
Affiliation(s)
- Shih Chieh Chang
- Medicinal Chemistry, Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, Victoria 3052, Australia
| | | | | | | | | | | | | |
Collapse
|
5
|
Norton RS. Mu-conotoxins as leads in the development of new analgesics. Molecules 2010; 15:2825-44. [PMID: 20428082 PMCID: PMC6257286 DOI: 10.3390/molecules15042825] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2010] [Revised: 04/06/2010] [Accepted: 04/12/2010] [Indexed: 02/02/2023] Open
Abstract
Voltage-gated sodium channels (VGSCs) contain a specific binding site for a family of cone shell toxins known as mu-conotoxins. As some VGSCs are involved in pain perception and mu-conotoxins are able to block these channels, mu-conotoxins show considerable potential as analgesics. Recent studies have advanced our understanding of the three-dimensional structures and structure-function relationships of the mu-conotoxins, including their interaction with VGSCs. Truncated peptide analogues of the native toxins have been created in which secondary structure elements are stabilized by non-native linkers such as lactam bridges. Ultimately, it would be desirable to capture the favourable analgesic properties of the native toxins, in particular their potency and channel sub-type selectivity, in non-peptide mimetics. Such mimetics would constitute lead compounds in the development of new therapeutics for the treatment of pain.
Collapse
Affiliation(s)
- Raymond S Norton
- Walter and Eliza Hall Institute of Medical Research, Victoria, Australia.
| |
Collapse
|
6
|
Abstract
Sea anemones produce a variety of toxic peptides and proteins, including many ion channel blockers and modulators, as well as potent cytolysins. This review describes the structures that have been determined to date for the major classes of peptide and protein toxins. In addition, established and emerging methods for structure determination are summarized and the prospects for modelling newly described toxins are evaluated. In common with most other classes of proteins, toxins display conformational flexibility which may play a role in receptor binding and function. The prospects for obtaining atomic resolution structures of toxins bound to their receptors are also discussed.
Collapse
|
7
|
Moran Y, Gordon D, Gurevitz M. Sea anemone toxins affecting voltage-gated sodium channels--molecular and evolutionary features. Toxicon 2009; 54:1089-101. [PMID: 19268682 DOI: 10.1016/j.toxicon.2009.02.028] [Citation(s) in RCA: 77] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
The venom of sea anemones is rich in low molecular weight proteinaceous neurotoxins that vary greatly in structure, site of action, and phyletic (insect, crustacean or vertebrate) preference. This toxic versatility likely contributes to the ability of these sessile animals to inhabit marine environments co-habited by a variety of mobile predators. Among these toxins, those that show prominent activity at voltage-gated sodium channels and are critical in predation and defense, have been extensively studied for more than three decades. These studies initially focused on the discovery of new toxins, determination of their covalent and folded structures, understanding of their mechanisms of action on different sodium channels, and identification of the primary sites of interaction of the toxins with their channel receptors. The channel binding site for Type I and the structurally unrelated Type III sea anemone toxins was identified as neurotoxin receptor site 3, a site previously shown to be targeted by scorpion alpha-toxins. The bioactive surfaces of toxin representatives from these two sea anemone types have been characterized by mutagenesis. These analyses pointed to heterogeneity of receptor site 3 at various sodium channels. A turning point in evolutionary studies of sea anemone toxins was the recent release of the genome sequence of Nematostella vectensis, which enabled analysis of the genomic organization of the corresponding genes. This analysis demonstrated that Type I toxins in Nematostella and other species are encoded by gene families and suggested that these genes developed by concerted evolution. The current review provides a brief historical description of the discovery and characterization of sea anemone toxins that affect voltage-gated sodium channels and delineates recent advances in the study of their structure-activity relationship and evolution.
Collapse
Affiliation(s)
- Yehu Moran
- Department of Plant Sciences, George S. Wise Faculty of Life Sciences, Tel Aviv University, Ramat Aviv, Tel Aviv 69978, Israel.
| | | | | |
Collapse
|
8
|
Smith JJ, Blumenthal KM. Site-3 sea anemone toxins: Molecular probes of gating mechanisms in voltage-dependent sodium channels. Toxicon 2007; 49:159-70. [PMID: 17095031 DOI: 10.1016/j.toxicon.2006.09.020] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
Sea anemone toxins, whose biological function is the capture of marine prey, are invaluable tools for studying the structure and function of mammalian voltage-gated sodium channels. Their high degree of specificity and selectivity have allowed for detailed analysis of inactivation gating and assignment of molecular entities responsible for this process. Because of their ability to discriminate among channel isoforms, and their high degree of structural conservation, these toxins could serve as important lead compounds for future pharmaceutical design.
Collapse
Affiliation(s)
- Jaime J Smith
- Department of Biochemistry, School of Medicine and Biomedical Sciences, State University of New York, 3435 Main St. Buffalo, NY 14214, USA
| | | |
Collapse
|
9
|
Abstract
Site-3 toxins are small polypeptide venoms from scorpions, sea anemones, and spiders that bind with a high specificity to the extracellular surface of voltage-gated Na channels. After binding to a site near the S4 segment in domain IV the toxin causes disruption of the normal fast inactivation transition resulting in a marked prolongation of the action potentials of excitable tissues including those of cardiac and skeletal muscle and nerve. In this review we discuss the specific binding interactions between residues of the toxin and those of the Na channel, and the specific modification of Na channel kinetic behavior leading to a change in fast inactivation focusing on interactions deduced primarily from the study of sea anemone toxins and the cardiac Na channel (Na(V)1.5). We also illustrate the usefulness of site-3 toxins in the study of altered Na channel behavior by drug-modification.
Collapse
Affiliation(s)
- Dorothy A Hanck
- Department of Medicine, The University of Chicago, Chicago, IL 60637, USA.
| | | |
Collapse
|
10
|
Smith JJ, Alphy S, Seibert AL, Blumenthal KM. Differential Phospholipid Binding by Site 3 and Site 4 Toxins. J Biol Chem 2005; 280:11127-33. [PMID: 15632158 DOI: 10.1074/jbc.m412552200] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
It has been shown recently that polypeptide toxins that modulate the gating properties of voltage-sensitive cation channels are able to bind to phospholipid membranes, leading to the suggestion that these toxins are able to access a channel-binding site that remains membrane-restricted (Lee, S.-Y., and MacKinnon, R. (2004) Nature 430, 232-235). We therefore examined the ability of anthopleurin B (ApB), a sea anemone toxin that selectively modifies inactivation kinetics of Na(V)1.x channels, and ProTx-II, a spider toxin that modifies activation kinetics of the same channels, to bind to liposomes. Whereas ProTx-II can be quantitatively depleted from solution upon incubation with phosphatidylcholine/phosphatidylserine liposomes, ApB displays no discernible phospholipid binding activity. We therefore examined the activities of structurally unrelated site 3 and site 4 toxins derived from Leiurus and Centruroides venoms, respectively, in the same assay. Like ApB, the site 3 toxin LqqV shows no lipid binding activity, whereas the site 4 toxin Centruroides toxin II, like ProTx-II, is completely bound. We conclude that toxins that modify inactivation kinetics via binding to Na(V)1.x site 3 lack the ability to bind phospholipids, whereas site 4 toxins, which modify activation, have this activity. This inherent difference suggests that the conformation of domain II more closely resembles that of the K(V)AP channel than does the conformation of domain IV.
Collapse
Affiliation(s)
- Jaime J Smith
- Department of Biochemistry, School of Medicine and Biomedical Sciences, State University of New York, Buffalo, New York 14214, USA
| | | | | | | |
Collapse
|
11
|
Wang L, Ou J, Peng L, Zhong X, Du J, Liu Y, Huang Y, Liu W, Zhang Y, Dong M, Xu AL. Functional expression and characterization of four novel neurotoxins from sea anemone Anthopleura sp. Biochem Biophys Res Commun 2004; 313:163-70. [PMID: 14672713 DOI: 10.1016/j.bbrc.2003.11.102] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
The genes of four novel neurotoxins, named Hk2a, Hk7a, Hk8a, and Hk16a, were obtained from sea anemone Anthopleura sp. All four neurotoxins were composed of 47 amino acid residues and the variable residues among them were found in positions 14, 22, 25, and 37. To study their activities, the four toxins fused to the Escherichia coli thioredoxin were overexpressed by BL21 (DE3), cleaved off from the fusion partner, purified, and characterized with MALDI-TOF and CD assays. Contractile force studies of isolated SD atria indicated that rHk2a had the strongest and rHk7a the longest heart stimulation effect. Consequently, the Arg14, a highly conserved residue in various sea anemone neurotoxins, can be inferred to contribute to the duration but not the intensity of contraction-stimulating activity. Our work renders useful information to studies of sea anemone neurotoxins, especially to the clarification of the function of the disputative Arg14.
Collapse
Affiliation(s)
- Lei Wang
- Department of Biochemistry, College of Life Sciences, Sun Yat-sen (Zhongshan) University, Guangzhou 510275, People's Republic of China
| | | | | | | | | | | | | | | | | | | | | |
Collapse
|
12
|
Liu WH, Wang L, Wang YL, Peng LS, Wu WY, Peng WL, Jiang XY, Tu HB, Chen HP, Ou-Yang P, Xu AL. Cloning and characterization of a novel neurotoxin from the sea anemone Anthopleura sp. Toxicon 2003; 41:793-801. [PMID: 12782079 DOI: 10.1016/s0041-0101(03)00033-3] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
A full-length cDNA of neurotoxin (Hk2a) was isolated by RT-PCR of total RNA isolated from tentacles of Anthopleura sp. using degenerate oligonucleotide primers and 3',5'-RACE. The cDNA sequence of Hk2a encoded a polypeptide of 47 amino acids, which lacks a typical N-terminal signal sequences commonly found in proteins that are secreted via endoplasmic reticulum-Golgi pathway, indicating the possibility of secretion via a non-classical pathway. The neurotoxin has a predicted molecular mass of 4.8 kDa and a pI value of 7.62. The amino acid sequence of Hk2a is very similar to Anthopleurin C (Ap-C) and Neurotoxin I (Af I), and shares 95% amino acid sequence similarity to Ap-C. The coding region for the matured Hk2a toxin was cloned into the thioredoxin (TRX) fusion expression vector (pTRX) for the fusion expression in Escherichia coli. The recombinant polypeptide of Hk2a (rHk2a) was purified by the affinity chromatography, 15 mg/l of rHk2a was obtained after the digestion with protease 3C and further purification. The molecular weight of rHk2a (5.078 kDa) obtained by MALDI-TOF was very close to that (5Da) calculated from the sequence. The results of the UV-circular dichroism spectra of rHk2a indicates that its secondary structure is similar to that of Ap-B (), having 61.7% beta-sheet and no alpha-helix. Investigation on pharmacological effects of rHk2a in vitro was undertaken, and it was found that LD(50) of rHk2a was 1.4 mg/kg on NIH mice (i.p.). The rHk2a was demonstrated to increase contracting activity on isolated SD rat atria with the enhancing degree reaching 343.5+/-160.5%. The increase in contractile amplitude reached a plateau value within 3-5 min after addition of this toxin.
Collapse
Affiliation(s)
- Wen-Hua Liu
- The Open Laboratory for Marine Functional Genomics of State High-Tech Development, Department of Biochemistry, College of Life Sciences, Sun Yat-Sen University, Guangzhou 510275, People's Republic of China
| | | | | | | | | | | | | | | | | | | | | |
Collapse
|
13
|
Affiliation(s)
- R J French
- Department of Physiology and Biophysics, University of Calgary, Alberta, Canada
| | | |
Collapse
|
14
|
Anderluh G, Podlesek Z, Macek P. A common motif in proparts of Cnidarian toxins and nematocyst collagens and its putative role. BIOCHIMICA ET BIOPHYSICA ACTA 2000; 1476:372-6. [PMID: 10669802 DOI: 10.1016/s0167-4838(99)00237-x] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/16/2022]
Abstract
In Cnidarians, cnidoblast cells contain organelles called cnidocysts, which are believed to be the product of an extremely complex regulated secretory pathway. When matured, these stinging organelles are capable of storing and delivering toxins. We hypothesized that translated nematocyst proteins might comprise specific sequences serving as signals in sorting to the organelle. A sodium channel neurotoxin from the sea anemone Actinia equina was cloned and the toxin precursor sequence was compared to those of nematocyst collagens, pore-forming toxins and ion channel neurotoxins. It was found that all the analyzed sequences possess a highly conserved stretch of nine amino acid residues ending with Lys-Arg N-terminally of the mature region.
Collapse
Affiliation(s)
- G Anderluh
- Department of Biology, Biotechnical Faculty, University of Ljubljana, Vecna pot 111, 1000, Ljubljana, Slovenia.
| | | | | |
Collapse
|
15
|
El-Sherif N, Caref EB, Chinushi M, Restivo M. Mechanism of arrhythmogenicity of the short-long cardiac sequence that precedes ventricular tachyarrhythmias in the long QT syndrome. J Am Coll Cardiol 1999; 33:1415-23. [PMID: 10193747 DOI: 10.1016/s0735-1097(98)00700-1] [Citation(s) in RCA: 47] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
OBJECTIVES The purpose of this study was to investigate the electrophysiologic mechanism(s) that underlie the transition of one or more short-long (S-L) cardiac sequences to ventricular tachyarrhythmias (VTs) in the long QT syndrome. BACKGROUND One or more S-L cardiac cycles, usually the result of a ventricular bigeminal rhythm, frequently precedes the onset of VT in patients with either normal or prolonged QT interval. Electrophysiologic mechanisms that underlie this relationship have not been fully explained. METHODS We investigated electrophysiologic changes associated with the transition of a S-L cardiac sequence to VT in the canine anthopleurin-A model, a surrogate of LQT3. Experiments were performed on 12 mongrel puppies after administration of anthopleurin-A. Correlation of tridimensional activation and repolarization patterns was obtained from up to 384 electrograms. Activation-recovery intervals were measured from unipolar electrograms and were considered to represent local repolarization. RESULTS We analyzed 24 different episodes of a S-L sequence that preceded VT obtained from 12 experiments. The VT followed one S-L sequence (five episodes), two to five S-L sequences (12 episodes) and more than five S-L sequences (seven episodes). The single premature ventricular beats coupled to the basic beats were consistently due to a subendocardial focal activity (SFA). There were two basic mechanisms for the development of VT after one or more S-L sequences: 1) in 10 examples of a S-L sequence due to a stable unifocal bigeminal rhythm, the occurrence of a second SFA, which arose consistently from a different site, infringed on the pattern of dispersion of repolarization (DR) of the first SFA to initiate reentrant excitation; 2) in the remaining 14 episodes of a S-L sequence, a slight lengthening (50 to 150 ms) in one or more preceding cycle lengths (CLs) resulted in alterations of the spatial pattern of DR at key sites to promote reentry. The lengthening of the preceding CL produced differentially a greater degree of prolongation of repolarization at midmyocardial and endocardial sites compared with epicardial sites with consequent increase of DR. The increased DR at key adjacent sites resulted in the development of de novo zones of functional conduction block and/or slowed conduction to create the necessary prerequisites for successful reentry. CONCLUSIONS The occurrence of VT after one or more S-L cardiac sequences was due to well defined electrophysiologic changes with predictable consequences that promoted reentrant excitation.
Collapse
Affiliation(s)
- N El-Sherif
- Department of Medicine, State University of New York Health Science Center and Veterans Affairs Medical Center, Brooklyn 11203, USA.
| | | | | | | |
Collapse
|
16
|
Lee KC, Crowe AJ, Barton MC. p53-mediated repression of alpha-fetoprotein gene expression by specific DNA binding. Mol Cell Biol 1999; 19:1279-88. [PMID: 9891062 PMCID: PMC116057 DOI: 10.1128/mcb.19.2.1279] [Citation(s) in RCA: 138] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/1998] [Accepted: 10/27/1998] [Indexed: 02/06/2023] Open
Abstract
Aberrant expression of the alpha-fetoprotein (AFP) gene is characteristic of a majority of hepatocellular carcinoma cases and serves as a diagnostic tumor-specific marker. By dissecting regulatory mechanisms through electromobility gel shift, transient-transfection, Western blot, and in vitro transcription analyses, we find that AFP gene expression is controlled in part by mutually exclusive binding of two trans-acting factors, p53 and hepatic nuclear factor 3 (HNF-3). HNF-3 protein activates while p53 represses AFP transcription through sequence-specific binding within the previously identified AFP developmental repressor domain. A single mutation within the DNA binding domain of p53 protein or a mutation of the p53 DNA binding element within the AFP developmental repressor eliminates p53-repressive effects in both transient-transfection and cell-free expression systems. Coexpression of p300 histone acetyltransferase, which has been shown to acetylate p53 and increase specific DNA binding, amplifies the p53-mediated repression. Western blot analysis of proteins present in developmentally staged, liver nuclear extracts reveal a one-to-one correlation between activation of p53 protein and repression of AFP during hepatic development. Induction of p53 in response to actinomycin D or hypoxic stress decreases AFP expression. Studies in fibroblast cells lacking HNF-3 further support a model for p53-mediated repression that is both passive through displacement of a tissue-specific activating factor and active in the presence of tissue-specific corepressors. This mechanism for p53-mediated repression of AFP gene expression may be active during hepatic differentiation and lost in the process of tumorigenesis.
Collapse
Affiliation(s)
- K C Lee
- Department of Molecular Genetics, Biochemistry, and Microbiology, University of Cincinnati, Cincinnati, Ohio 45267-0524, USA
| | | | | |
Collapse
|
17
|
Chinushi M, Restivo M, Caref EB, El-Sherif N. Electrophysiological basis of arrhythmogenicity of QT/T alternans in the long-QT syndrome: tridimensional analysis of the kinetics of cardiac repolarization. Circ Res 1998; 83:614-28. [PMID: 9742057 DOI: 10.1161/01.res.83.6.614] [Citation(s) in RCA: 95] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Tachycardia-dependent QT/T alternans occurs in patients with the congenital or idiopathic form of long-QT syndrome (LQTS) and may presage the onset of polymorphic ventricular tachyarrhythmias. To examine the electrophysiological basis of arrhythmogenicity of QT/T alternans in LQTS, the tridimensional repolarization pattern of QT/T alternans was studied in the anthopleurin-A model of LQTS, a surrogate for LQT3. In 11 anesthetized mongrel puppies, tridimensional repolarization and activation patterns were analyzed from 256 to 384 unipolar electrograms. Cardiac repolarization was evaluated as the activation-recovery interval (ARI) of local electrograms. To induce QT/T alternans, the pacing cycle length (CL) was abruptly shortened in steps of 50 ms from a basic drive of 1000 ms. ARIs were calculated at epicardial (Epi), midmyocardial (Mid), and endocardial (End) sites. ARI restitution at each site was assessed by using a single premature stimulation delivered after the basic drive. ARI alternans occurred at longer CLs at Mid sites compared with End and Epi sites, and the magnitude of alternans at Mid sites was greater. Two factors contributed to the modulation of ARI during QT/T alternans: (1) differences in restitution kinetics at Mid sites, characterized by larger DeltaARI and a slower time constant (tau), and (2) differences in diastolic intervals resulting in different input to restitution at the same constant CL. These 2 factors could explain not only the onset of alternans at Mid sites at longer CLs but also the critical observation that ARI dispersion between Epi and Mid sites during alternans was greater than during the slower basic CL. Marked ARI alternans could be present in local electrograms without manifest alternation of the QT/T segment in the surface ECG. The latter was seen at critically short CLs associated with reversal of the gradient of ARI between Epi and Mid sites, with a consequent reversal of polarity of the intramyocardial QT wave in alternate cycles. The arrhythmogenicity of QT/T alternans was primarily due to the greater degree of spatial dispersion of repolarization during alternans than during slower rates not associated with alternans. This could result in functional conduction block and reentrant ventricular tachyarrhythmias during the fixed drive associated with alternans.
Collapse
Affiliation(s)
- M Chinushi
- From the Cardiology Division, Department of Medicine, State University of New York Health Science Center, and Veterans Affairs Medical Center, Brooklyn, NY, USA
| | | | | | | |
Collapse
|
18
|
Benzinger GR, Kyle JW, Blumenthal KM, Hanck DA. A specific interaction between the cardiac sodium channel and site-3 toxin anthopleurin B. J Biol Chem 1998; 273:80-4. [PMID: 9417050 DOI: 10.1074/jbc.273.1.80] [Citation(s) in RCA: 98] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
The polypeptide neurotoxin anthopleurin B (ApB) isolated from the venom of the sea anemone Anthopleura xanthogrammica is one of a family of toxins that bind to the extracellular face of voltage-dependent sodium channels and retard channel inactivation. Because most regions of the sodium channel known to contribute to inactivation are located intracellularly or within the membrane bilayer, identification of the toxin/channel binding site is of obvious interest. Recently, mutation of a glutamic acid residue on the extracellular face of the fourth domain of the rat neuronal sodium channel (rBr2a) was shown to disrupt toxin/channel binding (Rogers, J. C., Qu, Y. S., Tanada, T. N., Scheuer, T., and Catterall, W. A. (1996) J. Biol. Chem. 271, 15950-15962). A negative charge at this position is highly conserved between mammalian sodium channel isoforms. We have constructed mutations of the corresponding residue (Asp-1612) in the rat cardiac channel isoform (rH1) and shown that the lowered affinity occurs primarily through an increase in the toxin/channel dissociation rate koff. Further, we have used thermodynamic mutant cycle analysis to demonstrate a specific interaction between this anionic amino acid and Lys-37 of ApB (DeltaDeltaG = 1.5 kcal/mol), a residue that is conserved among many sea anemone toxins. Reversal of the charge at Asp-1612, as in the mutant D1612R, also affects channel inactivation independent of toxin (-14 mV shift in channel availability). Binding of the toxin to Asp-1612 may therefore contribute both to toxin/channel affinity and to transduction of the effects of the toxin on channel kinetics.
Collapse
Affiliation(s)
- G R Benzinger
- Department of Committee on Neurobiology, The University of Chicago, Chicago, Illinois 60637, USA
| | | | | | | |
Collapse
|
19
|
Kelso GJ, Blumenthal KM. Identification and characterization of novel sodium channel toxins from the sea anemone Anthopleura xanthogrammica. Toxicon 1998; 36:41-51. [PMID: 9604281 DOI: 10.1016/s0041-0101(97)00064-0] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Six new toxins from the sea anemone Anthopleura xanthogrammica were identified using a molecular biological approach. Five of these novel isoforms resemble the 47 residue type I long polypeptides native to Anthopleura elegantissima, Anthopleura fuscoviridis and Anemonia sulcata, while one appears to be chimera of the two previously identified 49 residue toxins native to A. xanthogrammica. Four of these toxins were expressed in bacteria, purified and characterized by ion flux assays in RT4-B and N1E-115 cell lines expressing the cardiac and neuronal Na channel isoforms, respectively. The novel 47 residue toxin isoforms form a new subclass within the A. xanthogrammica neurotoxin family, although they are related to previously described anemone toxins. One of the three 47 residue toxins characterized, PCR2-10, enhances veratridine-dependent sodium uptake, displaying a K0.5 of 329 nM and 1354 nM in RT4-B and N1E-115 cell lines, respectively. The novel 49 residue toxin, PCR3-7, interacts with the sodium channel with even higher affinity, enhancing sodium uptake with a K0.5 of 47 nM and 108 nM in RT4-B and N1E-115 cells, respectively.
Collapse
Affiliation(s)
- G J Kelso
- Department of Molecular Genetics, Biochemistry and Microbiology, University of Cincinnati College of Medicine, OH 45267-0524, USA
| | | |
Collapse
|
20
|
El-Sherif N, Chinushi M, Caref EB, Restivo M. Electrophysiological mechanism of the characteristic electrocardiographic morphology of torsade de pointes tachyarrhythmias in the long-QT syndrome: detailed analysis of ventricular tridimensional activation patterns. Circulation 1997; 96:4392-9. [PMID: 9416909 DOI: 10.1161/01.cir.96.12.4392] [Citation(s) in RCA: 114] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
BACKGROUND The long-QT syndrome (LQTS) is an electrophysiological (EP) entity characterized by prolongation of cardiac repolarization and the occurrence of polymorphic ventricular tachyarrhythmias (VTs), sometimes with a twisting QRS morphology, better known as torsade de pointes (TdP). In the present study, detailed analysis of ventricular tridimensional activation patterns during nonsustained TdP VT was performed to provide an EP mechanism of the periodic transition in QRS axis. METHODS AND RESULTS The studies were conducted with the anthopleurin-A canine model of LQTS. Tridimensional isochronal maps of ventricular activation were constructed from 256 bipolar electrograms obtained from the use of 64 plunge needle electrodes. In 26 episodes of nonsustained TdP VT, detailed activation maps could be accurately constructed during QRS-axis transitions in surface ECGs. The initial beat of all VTs consistently arose as a subendocardial focal activity, whereas subsequent beats were due to reentrant excitation in the form of rotating scrolls. The VT ended when reentrant excitation was terminated. In 22 of 26 episodes, the transition in QRS axis coincided with the transient bifurcation of a predominantly single rotating scroll into two simultaneous scrolls involving both the right ventricle and left ventricle separately. The common mechanism for initiation or termination of bifurcation was the development of functional conduction block between the anterior or posterior right ventricle free wall and the ventricular septum. In 4 of 26 episodes, a fast polymorphic VT, with an apparent shift in QRS axis, was due to a predominantly single localized circuit that varied its location and orientation from beat to beat, with the majority of ventricular myocardium being activated in a centrifugal pattern. CONCLUSIONS The study provides for the first time an EP mechanism for the characteristic periodic transition of the QRS axis during TdP VT in the LQTS.
Collapse
Affiliation(s)
- N El-Sherif
- Department of Medicine, State University of New York Health Science Center and Veterans Affairs Medical Center, Brooklyn 11203, USA.
| | | | | | | |
Collapse
|
21
|
Fletcher JI, Chapman BE, Mackay JP, Howden ME, King GF. The structure of versutoxin (delta-atracotoxin-Hv1) provides insights into the binding of site 3 neurotoxins to the voltage-gated sodium channel. Structure 1997; 5:1525-35. [PMID: 9384567 DOI: 10.1016/s0969-2126(97)00301-8] [Citation(s) in RCA: 103] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
BACKGROUND Versutoxin (delta-ACTX-Hv1) is the major component of the venom of the Australian Blue Mountains funnel web spider, Hadronyche versuta. delta-ACTX-Hv1 produces potentially fatal neurotoxic symptoms in primates by slowing the inactivation of voltage-gated sodium channels; delta-ACTX-Hv1 is therefore a useful tool for studying sodium channel function. We have determined the three-dimensional structure of delta-ACTX-Hv1 as the first step towards understanding the molecular basis of its interaction with these channels. RESULTS The solution structure of delta-ACTX-Hv1, determined using NMR spectroscopy, comprises a core beta region containing a triple-stranded antiparallel beta sheet, a thumb-like extension protruding from the beta region and a C-terminal 310 helix that is appended to the beta domain by virtue of a disulphide bond. The beta region contains a cystine knot motif similar to that seen in other neurotoxic polypeptides. The structure shows homology with mu-agatoxin-I, a spider toxin that also modifies the inactivation kinetics of vertebrate voltage-gated sodium channels. More surprisingly, delta-ACTX-Hv1 shows both sequence and structural homology with gurmarin, a plant polypeptide. This similarity leads us to suggest that the sweet-taste suppression elicited by gurmarin may result from an interaction with one of the downstream ion channels involved in sweet-taste transduction. CONCLUSIONS delta-ACTX-Hv1 shows no structural homology with either sea anemone or alpha-scorpion toxins, both of which also modify the inactivation kinetics of voltage-gated sodium channels by interacting with channel recognition site 3. However, we have shown that delta-ACTX-Hv1 contains charged residues that are topologically related to those implicated in the binding of sea anemone and alpha-scorpion toxins to mammalian voltage-gated sodium channels, suggesting similarities in their mode of interaction with these channels.
Collapse
Affiliation(s)
- J I Fletcher
- Department of Biochemistry University of Sydney Sydney, NSW 2006, Australia
| | | | | | | | | |
Collapse
|
22
|
Dias-Kadambi BL, Combs KA, Drum CL, Hanck DA, Blumenthal KM. The role of exposed tryptophan residues in the activity of the cardiotonic polypeptide anthopleurin B. J Biol Chem 1996; 271:23828-35. [PMID: 8798612 DOI: 10.1074/jbc.271.39.23828] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
Scorpion and sea anemone venoms contain several polypeptides that delay inactivation of voltage-sensitive sodium channels via interaction with a common site. In this report, we target exposed hydrophobic residues at positions 33 and 45 of anthopleurin B (ApB) by polymerase chain reaction mutagenesis to ascertain their contribution to toxin activity. Nonconservative replacements are not permitted at position 33, indicating that Trp-33 may play an important structural role. Strikingly, the relatively conservative substitution of Trp-33 by phenylalanine results in major reductions in binding affinity for both the cardiac and neuronal channel isoforms as measured by ion flux, whereas substitution with tyrosine is tolerated and exhibits near wild-type affinities, suggesting that either the ability to form a hydrogen bond or the amphiphilic nature of the side chain are important at this position. Electrophysiological analysis of W33F indicates that its diminished affinity is primarily due to a decreased association rate. Analysis of a panel of mutants at Trp-45 shows only modest changes in apparent binding affinity for both channel isoforms but significant effects on Vmax. In neuronal channels, the maximal levels of uptake for W45A/S/F are about 50% those seen with ApB. This effect is also observed for W45A and W45S in the cardiac model, wherein W45F is normal. These results suggest that a hydrophobic contact is involved in toxin-induced stabilization of the open conformation of the cardiac sodium channel. We conclude that Trp-33 contributes significantly to apparent affinity, whereas Trp-45 does not appear to affect binding per se. Furthermore, W33F is the first ApB mutant that displays a significantly altered association rate and may prove to be a useful probe of the channel binding site.
Collapse
Affiliation(s)
- B L Dias-Kadambi
- Department of Molecular Genetics, Biochemistry and Microbiology, University of Cincinnati, College of Medicine, Cincinnati, Ohio 45267-0524, USA
| | | | | | | | | |
Collapse
|
23
|
Monks SA, Norton RS, Curtain CC, Berliner LJ. Preparation and characterization of a biologically active spin-labeled sea anemone toxin. JOURNAL OF PROTEIN CHEMISTRY 1996; 15:427-34. [PMID: 8895087 DOI: 10.1007/bf01886849] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
A derivative of the polypeptide cardiostimulant anthopleurin-B(AP-B) labeled with the spin label 1-oxyl 2,2,6,6-tetramethyl-4-piperidinyloxycarbonyl azide has been prepared and characterized. The product was found by mass spectrometry to be labeled at a single site, which amino acid sequencing showed to be the N-terminus. It also retained positive inotropic activity when assayed on isolated guinea pig atria. The spin-labeled (SL) product was found to exist in two distinct conformations by reversed-phase HPLC and in at least two conformations by electron spin resonance spectroscopy (ESR) over the pH range 2-9. The ESR data also show evidence for multimetric states of SL-AP-B over the pH range 2-9, with maximum aggregation at pH 4.5-5, and a slow disaggregation when the pH is adjusted to 8-9. The presence of multiple conformers of SL-AP-B and its tendency to aggregate render it unsuitable for high-resolution NMR structural studies of the isolated ligand, but the retention of activity may make it useful for studies of the sodium-channel-bound form of the molecule.
Collapse
Affiliation(s)
- S A Monks
- NMR Laboratory, Biomolecular Research Institute, Parkville, Australia
| | | | | | | |
Collapse
|
24
|
Dias-Kadambi BL, Drum CL, Hanck DA, Blumenthal KM. Leucine 18, a hydrophobic residue essential for high affinity binding of anthopleurin B to the voltage-sensitive sodium channel. J Biol Chem 1996; 271:9422-8. [PMID: 8621610 DOI: 10.1074/jbc.271.16.9422] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
Anthopleurin B is a potent anemone toxin that binds with nanomolar affinity to the cardiac and neuronal isoforms of the voltage-gated sodium channel. A cationic cluster that includes Arg-12, Arg-14 and Lys-49 has been shown previously to be important in this interaction. In this study, we have used site-directed mutagenesis to determine the contribution to activity of two aliphatic residues, Leu-18 and Ile-43, that have previously been experimentally inaccessible. Leu-18, a residue proximal to the cationic cluster, plays a critical role in defining the high affinity of the toxin. In ion flux studies, this is exemplified by the several hundredfold loss in affinity (231-672-fold) observed for both L18A and L18V toxins on either isoform of the sodium channel. When analyzed electrophysiologically, L18A, the most severely compromised mutant, also displays a substantial loss in affinity (34-fold and 328-fold) for the neuronal and cardiac isoforms. This difference in affinities may reflect an increased preference of the L18A mutant for the closed state of the neuronal channel. In contrast, Ile-43, a residue distal to the cationic cluster, plays at most a very modest role in affinity toward both isoforms of the sodium channel. Only conservative substitutions are tolerated at this position, implying that it may contribute to an important structural component. Our results indicate that Leu-18 is the most significant single contributor to the high affinity of Anthopleurin B identified to date. These results have extended the binding site beyond the cationic cluster to include Leu-18 and broadened our emphasis from the basic residues to include the crucial role of hydrophobic residues in toxin-receptor interactions.
Collapse
Affiliation(s)
- B L Dias-Kadambi
- Department of Molecular Genetics, Biochemistry and Microbiology, University of Cincinnati, College of Medicine, Cincinnati, Ohio 45267-0524, USA
| | | | | | | |
Collapse
|
25
|
Monks SA, Pallaghy PK, Scanlon MJ, Norton RS. Solution structure of the cardiostimulant polypeptide anthopleurin-B and comparison with anthopleurin-A. Structure 1995; 3:791-803. [PMID: 7582896 DOI: 10.1016/s0969-2126(01)00214-3] [Citation(s) in RCA: 51] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
BACKGROUND The polypeptide anthopleurin-B (AP-B) is one of a number of related toxins produced by sea anemones. AP-B delays inactivation of the voltage-gated sodium channel of excitable tissue. In the mammalian heart, this effect is manifest as an increase in the force of contraction. As a result, there is interest in exploiting the anthopleurins as lead compounds in the design of novel cardiac stimulants. Essential to this endeavour is a high-resolution solution structure of the molecule describing the positions of functionally important side chains. RESULTS AP-B exists in multiple conformations in solution as a result of cis-trans isomerization about the Gly40-Pro41 peptide bond. The solution structure of the major conformer of AP-B has been determined by two-dimensional 1H NMR at pH 4.5 and 25 degrees C. The core structure is a four-stranded, antiparallel beta-sheet (residues 2-4, 20-23, 34-37 and 45-48) and includes several beta-turns (6-9, 25-28, 30-33). Three loops connect the beta-strands, the longest and least well defined being the first loop, extending from residues 8-17. These features are shared by other members of this family of sea anemone toxins. The locations of a number of side chains which are important for the cardiac stimulatory activity of AP-B are well defined in the structures. CONCLUSIONS We have described the solution structure of AP-B and compared it with that of AP-A, from which it differs by substitutions at seven amino acid positions. It shares an essentially identical fold with AP-A yet is about 10-fold more active. Comparison of the structures, particularly in the region of residues essential for activity, gives a clearer indication of the location and extent of the cardioactive pharmacophore in these polypeptides.
Collapse
Affiliation(s)
- S A Monks
- NMR Laboratory, Biomolecular Research Institute, Parkville, Australia
| | | | | | | |
Collapse
|
26
|
Rosenthal J, Hsu S, Schneider D, Gentile L, Messier N, Vaslet C, Hawrot E. Functional expression and site-directed mutagenesis of a synthetic gene for alpha-bungarotoxin. J Biol Chem 1994. [DOI: 10.1016/s0021-9258(19)78107-1] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
|
27
|
Gallagher M, Blumenthal K. Importance of the unique cationic residues arginine 12 and lysine 49 in the activity of the cardiotonic polypeptide anthopleurin B. J Biol Chem 1994. [DOI: 10.1016/s0021-9258(17)42342-8] [Citation(s) in RCA: 41] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
|
28
|
Khera P, Blumenthal K. Role of the cationic residues arginine 14 and lysine 48 in the function of the cardiotonic polypeptide anthopleurin B. J Biol Chem 1994. [DOI: 10.1016/s0021-9258(17)42199-5] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
|