Halcurin

Halcurin is a polypeptide neurotoxin from the sea anemone Halcurias sp.[1] Based on sequence homology to type 1 and type 2 sea anemone toxins it is thought to delay channel inactivation by binding to the extracellular site 3 on the voltage gated sodium channels in a membrane potential-dependent manner.[1]

## Contents

* 1 Source and etymology
* 2 Chemistry
* 3 General information
* 4 Target
* 5 Mode of action
* 6 Toxicity
* 7 References
* 8 External links

## Source and etymology

The polypeptide toxin halcurin is named after its source: the sea anemone genus Halcurias,[1] which are ocean dwelling solitary invertebrates.[2]

## Chemistry

The amino acid sequence of halcurin is: VACRCESDGP DVRSATFTGT VDLWNCNTGW HKCIATYTAV ASCCKKD; it consists of 47 amino acids and has a molecular weight of 5,086 Da [1]

## General information

A classification of sea anemone polypeptide neurotoxins has been proposed based on their amino acid sequence, dividing the group into three classes of sodium channel toxins.[3] Halcurin is structurally homologous with type 2 toxins, but also has sequence homology to type 1 toxins.[1] Type 1 and 2 toxins are composed of 46 to 49 amino acid residues, and cross-linked by three disulfide bridges.[2] Ten residues including six Cysteine (Cys) residues are completely conserved between type 1 and 2 toxins.[3] Therefore, it is possible that type 1 and 2 toxins have evolved from Halcurin as a common ancestor.[1]

## Target

Type 1 and 2 toxins are known to target neurotoxin receptor site 3.[4] Based on the structural homology of halcurin with sea anemone toxin type 1 and 2 [1] it is likely to target neurotoxin receptor site 3. Neurotoxin receptor site 3 is predicted to be at the domain IV of voltage gated sodium channel, more specifically at the extracellular loop of segment 3-4. These voltage gated sodium channels are found in neurons, skeletal muscles, and cardiac muscles.[2]

## Mode of action

The domain III and IV intracellular loop structure acts as a fast inactivation gate in voltage gated sodium channels.[5] Sea anemone toxin type 1 and 2 slow or prevent the conformational changes in domain IV segment 3-4 loop required for inactivation of the channel.[6] Based on the structural homology of halcurin to sea anemone neurotoxin type 1 and 2,[1] it is likely to have a similar mode of action.

## Toxicity

Halcurin has a median lethal dose (LD50) of 5.8 μg/kg for crabs, but it does not show lethality in mice.[1]

## References

1. ↑ 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 Ishida, M (Apr 1997). "Halcurin, a polypeptide toxin in the sea anemone Halcurias sp., with a structural resemblance to type 1 and 2 toxins". Toxicon 35 (4): 537–544. doi:10.1016/s0041-0101(96)00143-2. PMID 9133708.
2. ↑ 2.0 2.1 2.2 Bosmans, F (Dec 2002). "The sea anemone Bunodosoma granulifera contains surprisingly efficacious and potent insect-selective toxins". FEBS 532 (1–2): 131–134. doi:10.1016/s0014-5793(02)03653-0. PMID 12459477. Bibcode: 2002FEBSL.532..131B.
3. ↑ 3.0 3.1 Norton, RS (1991). "Structure and structure-function relationships of sea anemone proteins that interact with the sodium channel". Toxicon 29 (9): 1051–1084. doi:10.1016/0041-0101(91)90205-6. PMID 1686683. Bibcode: 1991Txcn...29.1051N.
4. ↑ Honma, Tomohiro; Shiomi, Kazuo (2006). "Peptide Toxins in Sea Anemones: Structural and Functional Aspects". Marine Biotechnology 8 (1): 1–10. doi:10.1007/s10126-005-5093-2. PMID 16372161. Bibcode: 2006MarBt...8....1H.
5. ↑ Caterall, WA (1995). "Structure and function of voltage-gated ion channels". Annual Review of Biochemistry 64: 493–531. doi:10.1146/annurev.bi.64.070195.002425. PMID 7574491.
6. ↑ Rogers, JC (Jul 1996). "Molecular determinants of high affinity binding of alpha-scorpion toxin and sea anemone toxin in the S3-S4 extracellular loop in domain IV of the Na+ channel alpha subunit". Journal of Biological Chemistry 271 (27): 15950–15962. doi:10.1074/jbc.271.27.15950. PMID 8663157.

## External links

* Uniprot Halcurin (P0C5G6)

* v
* t
* e

* Toxins
* enterotoxin
* neurotoxin
* hemotoxin
* cardiotoxin
* phototoxin

Bacterial
toxins|

| Exotoxin|

| Gram
positive|

| Bacilli|

| Clostridium:|

* tetani
* Tetanospasmin
* Tetanolysin
* perfringens
* Alpha toxin
* Enterotoxin
* difficile
* A
* B
* botulinum
* Botox

|

other:|

* Anthrax toxin
* Listeriolysin O

Cocci|

* Streptolysin
* Leukocidin
* Panton-Valentine leukocidin

Staphylococcus|

* Staphylococcus aureus alpha/beta/delta
* Exfoliatin
* Toxic shock syndrome toxin
* Staphylococcal Enterotoxin B (SEB)

Actinomycetota|

* Cord factor
* Diphtheria toxin

Gram
negative|

* Shiga toxin/Verotoxin
* E. coli heat-stable enterotoxin
* Cholera toxin/Heat-labile enterotoxin
* Pertussis toxin
* Pseudomonas exotoxin
* Extracellular adenylate cyclase

Mechanisms|

* type I
* Superantigen
* type II
* Pore-forming toxin
* type III
* AB toxin/AB5

Endotoxin|

* Lipopolysaccharide
* Lipid A
* Bacillus thuringiensis delta endotoxin
* Cry1Ac
* Cry3Bb1
* Other B. thuringiensis toxins
* Cry6Aa
* Cry34Ab1

Virulence
factor|

* Clumping factor A
* Fibronectin binding protein A

Mycotoxins|

* Aflatoxin
* Amatoxin (alpha-amanitin, beta-amanitin, gamma-amanitin, epsilon-amanitin)
* beta-Nitropropionic acid
* Citrinin
* Cytochalasin
* Ergotamine
* Fumonisin (Fumonisin B1, Fumonisin B2, Fumonisin B3, Fumonisin B4)
* Gliotoxin
* Ibotenic acid
* Lolitrem B
* Muscimol
* Ochratoxin
* Patulin
* Phalloidin
* Sterigmatocystin
* Trichothecene
* Vomitoxin
* Zeranol
* Zearalenone

Plant toxins|

* Amygdalin
* Anisatin
* Antiarin
* Brucine
* Chaconine
* Cicutoxin
* Daphnin
* Delphinine
* Divicine
* Djenkolic acid
* Falcarinol
* Gossypol
* Helenalin
* Ledol
* Linamarin
* Lotaustralin
* Mimosine
* Oenanthotoxin
* Oleandrin
* Persin
* Protoanemonin
* Pseudaconitine
* Retronecine
* Resiniferatoxin
* Scopolamine
* Solamargine
* Solanidine
* Solanine
* Solasodamine
* Solasodine
* Solasonine
* Solauricidine
* Solauricine
* Strychnine
* Swainsonine
* Tagetitoxin
* Tinyatoxin
* Tomatine
* Toxalbumin
* Abrin
* Ricin
* Tutin

Invertebrate
toxins|

| Scorpion:|

* Androctonus australis hector insect toxin
* Charybdotoxin
* Maurotoxin
* Agitoxin
* Margatoxin
* Slotoxin
* Scyllatoxin
* Hefutoxin
* HgeTx1
* HsTx1
* Lq2
* Birtoxin
* Bestoxin
* BmKAEP
* Phaiodotoxin
* Imperatoxin
* Pi3

|

spider:|

* Latrotoxin
* Alpha-latrotoxin
* CSTX
* Cupiennins
* PhTx3
* Stromatoxin
* Vanillotoxin
* Huwentoxin

Mollusca:|

* Conotoxin
* Eledoisin
* Onchidal
* Saxitoxin
* Tetrodotoxin

Vertebrate
toxins|

| Fish:|

* Ciguatera
* Tetrodotoxin

|

Amphibian:|

* (+)-Allopumiliotoxin 267A
* Batrachotoxin
* Bufotoxins
* Arenobufagin
* Bufotalin
* Bufotenin
* Cinobufagin
* Marinobufagin
* Epibatidine
* Histrionicotoxin
* Pumiliotoxin 251D
* Samandarin
* Samandaridine
* Tarichatoxin
* Zetekitoxin AB

Reptile/
Snake venom:|

* Bungarotoxin
* Alpha-Bungarotoxin
* Beta-Bungarotoxin
* Calciseptine
* Taicatoxin
* Calcicludine
* Cardiotoxin III

* note: some toxins are produced by lower species and pass through intermediate species

* Category

* v
* t
* e

Ion channel modulators

Calcium|

| VDCCs|

| Blockers|

* L-type-selective: Dihydropyridines: Amlodipine
* Aranidipine
* Azelnidipine
* Barnidipine
* Clevidipine
* Cronidipine
* Darodipine
* Dexniguldipine
* Elgodipine
* Elnadipine
* Felodipine
* Flordipine
* Furnidipine
* Iganidipine
* Isradipine
* Lacidipine
* Lemildipine
* Lercanidipine
* Levamlodipine
* Levniguldipine
* Manidipine
* Mepirodipine
* Mesudipine
* Nicardipine
* Nifedipine
* Niguldipine
* Niludipine
* Nilvadipine
* Nimodipine
* Nisoldipine
* Nitrendipine
* Olradipine
* Oxodipine
* Palonidipine
* Pranidipine
* Ryodipine (riodipine)
* Sagandipine
* Sornidipine
* Teludipine
* Tiamdipine
* Trombodipine
* Vatanidipine; Diltiazem derivatives: Clentiazem
* Diltiazem
* Iprotiazem
* Nictiazem
* Siratiazem; Phenylalkylamines: Anipamil
* Dagapamil
* Devapamil
* Dexverapamil
* Emopamil
* Etripamil
* Falipamil
* Gallopamil
* Levemopamil
* Nexopamil
* Norverapamil
* Ronipamil
* Tiapamil
* Verapamil; Others: AH-1058
* Brinazarone
* Budiodarone
* Celivarone
* Cyproheptadine
* Dronedarone
* Fantofarone
* SR-33805
* Tetrahydropalmatine

* N-type-selective: ω-Conotoxins
* ω-Conotoxin GVIA
* Caroverine
* Huwentoxin XVI
* Leconotide (ω-conotoxin CVID)
* PD-173212
* Ralfinamide
* Safinamide
* Z160
* Ziconotide (ω-conotoxin MVIIA)

* P-type-selective: ω-Agatoxin IVA
* ω-Agatoxin IVB

* R-type-selective: SNX-482

* T-type-selective: ABT-639
* ML-218
* Niflumic acid
* NNC 55-0396
* ProTx I
* Z944
* Zonisamide

* Non-selective: ω-Agatoxin TK
* ω-Conotoxin MVIIC
* Benidipine
* Bepridil
* Cilnidipine
* Cinnarizine
* Dotarizine
* Efonidipine
* Flunarizine
* Lamotrigine
* Levetiracetam
* Lomerizine
* Loperamide
* Mibefradil
* NP078585
* Ruthenium red
* TROX-1

* α2δ subunit-selective (gabapentinoids): 4-Methylpregabalin
* Arbaclofen
* Arbaclofen placarbil
* Atagabalin
* Baclofen
* Gabapentin
* Gabapentin enacarbil
* Imagabalin
* Mirogabalin
* PD-200,347
* PD-217,014
* PD-299,685
* Phenibut
* Pregabalin

* Others/unsorted: Bencyclane
* Berbamine
* Bevantolol
* Canadine
* Carboxyamidotriazole
* Cycleanine
* Dauricine
* Dimeditiapramine
* Diproteverine
* Enpiperate
* Eperisone
* Elpetrigine
* Ethadione
* Ethanol (alcohol)
* Ethosuximide
* Fasudil
* Fendiline
* Fostedil
* Imepitoin
* JTV-519
* Lidoflazine
* Magnesium
* Manoalide
* Mesuximide
* Monatepil
* Naftopidil
* Ochratoxin A
* Osthol
* Otilonium bromide
* Paramethadione
* Phensuximide
* Pinaverium bromide
* Prenylamine
* Rhynchophylline
* Sesamodil
* Silperisone
* Sipatrigine
* Terodiline
* Tetrandrine
* Tolperisone
* Trimethadione
* Valperinol

|

Activators|

* L-type-selective: Bay K8644

Potassium|

| VGKCs|

| Blockers|

* 3,4-Diaminopyridine (amifampridine)
* 4-Aminopyridine (fampridine/dalfampridine)
* Adekalant
* Almokalant
* Amiodarone
* Azimilide
* Bretylium
* Bunaftine
* Charybdotoxin
* Clamikalant
* Conotoxins
* Dalazatide
* Dendrotoxin
* Dofetilide
* Dronedarone
* E-4031
* Hanatoxin
* HgeTx1
* HsTx1
* Ibutilide
* Inakalant
* Kaliotoxin
* Linopirdine
* Lolitrem B
* Maurotoxin
* Nifekalant
* Notoxin
* Paxilline
* Pinokalant
* Quinidine
* ShK-186
* Sotalol
* Tedisamil
* Terikalant
* Tetraethylammonium
* Vernakalant

* hERG (KCNH2, Kv11.1)-specific: Ajmaline
* Amiodarone
* AmmTX3
* Astemizole
* Azaspiracid
* AZD1305
* Azimilide
* Bedaquiline
* BeKm-1
* BmTx3
* BRL-32872
* Chlorpromazine
* Cisapride
* Clarithromycin
* Darifenacin
* Dextropropoxyphene
* Diallyl trisulfide
* Domperidone
* E-4031
* Ergtoxins
* Erythromycin
* Gigactonine
* Haloperidol
* Ketoconazole
* Norpropoxyphene
* Orphenadrine
* Pimozide
* PNU-282,987
* Promethazine
* Quinidine
* Ranolazine
* Roxithromycin
* Sertindole
* Solifenacin
* Tamulotoxin
* Terodiline
* Terfenadine
* Thioridazine
* Tolterodine
* Vanoxerine
* Vernakalant

* KCNQ (Kv7)-specific: Linopirdine
* XE-991
* Spooky toxin (SsTx)

|

Activators|

* KCNQ (Kv7)-specific: Flupirtine
* Retigabine

IRKs|

| Blockers|

* KATP-specific: Acetohexamide
* Carbutamide
* Chlorpropamide
* Glibenclamide (glyburide)
* Glibornuride
* Glicaramide
* Gliclazide
* Glimepiride
* Glipizide
* Gliquidone
* Glisoxepide
* Glyclopyramide
* Glycyclamide
* Metahexamide
* Mitiglinide
* Nateglinide
* Repaglinide
* Tolazamide
* Tolbutamide

* GIRK-specific: Barium
* Caramiphen
* Cloperastine
* Clozapine
* Dextromethorphan
* Ethosuximide
* Ifenprodil
* Tertiapin
* Tipepidine

|

Activators|

* KATP-specific: Aprikalim
* Bimakalim
* Cromakalim
* Diazoxide
* Emakalim
* Levcromakalim
* Mazokalim
* Minoxidil
* Naminidil
* Nicorandil
* Pinacidil
* Rilmakalim
* Sarakalim

* GIRK-specific: ML-297 (VU0456810)

KCa|

| Blockers|

* BKCa-specific: Ethanol (alcohol)
* GAL-021

|

Activators|

* BKCa-specific: Flufenamic acid
* Meclofenamic acid
* Niflumic acid
* Nimesulide
* Rottlerin (mallotoxin)
* Tolfenamic acid

K2Ps|

| Blockers|

* 12-O-Tetradecanoylphorbol-13-acetate
* Arachidonic acid
* Fluoxetine
* Norfluoxetine

|

Activators|

* Riluzole

Sodium|

| VGSCs|

| Blockers|

* Antianginals: Ranolazine

* Antiarrhythmics (class I): Ajmaline
* Aprindine
* Disopyramide
* Dronedarone
* Encainide
* Flecainide
* Lidocaine
* Lorajmine
* Lorcainide
* Mexiletine
* Moricizine
* Pilsicainide
* Prajmaline
* Procainamide
* Propafenone
* Quinidine
* Sparteine
* Tocainide

* Anticonvulsants: Acetylpheneturide
* Carbamazepine
* Cenobamate
* Chlorphenacemide
* Elpetrigine
* Eslicarbazepine acetate
* Ethotoin
* Fosphenytoin
* Lacosamide
* Licarbazepine
* Mephenytoin
* Oxcarbazepine
* Oxitriptyline
* Phenacemide
* Pheneturide
* Phenytoin
* Rufinamide
* Sipatrigine
* Topiramate
* Sodium valproate
* Valnoctamide
* Valproate pivoxil
* Valproate semisodium
* Valproic acid
* Valpromide
* Zonisamide

* Local anesthetics: pFBT
* Amylocaine
* Articaine
* Benzocaine
* Bupivacaine (Levobupivacaine, Ropivacaine)
* Butacaine
* Butamben
* Chloroprocaine
* Cinchocaine
* Cocaine
* Cyclomethycaine
* Dimethocaine
* Diphenhydramine
* Etidocaine
* Hexylcaine
* Iontocaine
* Lidocaine
* Mepivacaine
* Meprylcaine
* Metabutoxycaine
* Orthocaine
* Piperocaine
* Prilocaine
* Procaine
* Propoxycaine
* Proxymetacaine
* Risocaine
* Tetracaine
* Trimecaine

* Analgesics: AZD-3161
* DSP-2230
* Funapide
* GDC-0276
* NKTR-171
* PF-04531083
* PF-05089771
* Ralfinamide
* Raxatrigine
* RG7893 (GDC-0287)

* Toxins: Conotoxins
* Neosaxitoxin
* Saxitoxin
* Tetrodotoxin
* Zetekitoxin AB

* Others: Buprenorphine
* Evenamide
* Menthol (mint)
* Safinamide
* Tricyclic antidepressants

|

Activators|

* Aconitine
* Atracotoxins (ω-Atracotoxin, Robustoxin, Versutoxin)
* Batrachotoxin
* Ciguatoxins
* Grayanotoxins
* Poneratoxin

ENaC|

| Blockers|

* Amiloride
* Benzamil
* Triamterene

|

Activators|

* Solnatide

ASICs|

| Blockers|

* A-317567
* Amiloride
* Aspirin
* Ibuprofen
* PcTX1

|

Chloride|

| CaCCs|

| Blockers|

* Crofelemer
* DIDS
* Ethacrynic acid
* Flufenamic acid
* Fluoxetine
* Furosemide
* Glibenclamide
* Mefloquine
* Mibefradil
* Niflumic acid

|

Activators|

* Carbachol

CFTR|

| Blockers|

* Glibenclamide
* Lonidamine
* Piretanide

|

Activators|

* 1,7-Phenanthroline
* 1,10-Phenanthroline
* 4,7-Phenanthroline
* 7,8-Benzoquinoline
* Ivacaftor
* Phenanthridine

Unsorted|

| Blockers|

* Bumetanide
* Flufenamic acid
* Meclofenamic acid
* Mefenamic acid
* Mepacrine
* Niflumic acid
* Talniflumate
* Tolfenamic acid
* Trifluoperazine

|

Others|

| TRPs|

* See here instead.

|

LGICs|

* See here instead.

See also: Receptor/signaling modulators • Transient receptor potential channel modulators

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*[v]: View this template
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*[VDCCs]: Voltage-dependent calcium channels
*[VGKCs]: Voltage-gated potassium channels
*[IRKs]: Inwardly rectifying potassium channel
*[KATP]: ATP-sensitive potassium channel
*[GIRK]: G protein-coupled inwardly-rectifying potassium channel
*[KCa]: Calcium-activated potassium channel
*[K2Ps]: Tandem pore domain potassium channel
*[VGSCs]: Voltage-gated sodium channels
*[ENaC]: Epithelial sodium channel
*[ASICs]: Acid-sensing ion channel
*[CaCCs]: Calcium-activated chloride channel
*[CFTR]: Cystic fibrosis transmembrane conductance regulator
*[TRPs]: Transient receptor potential channels
*[LGICs]: Ligand gated ion channels