Margatoxin (MgTX) is a

peptide Peptides (, ) are short chains of amino acids linked by peptide bonds. Long chains of amino acids are called proteins. Chains of fewer than twenty amino acids are called oligopeptides, and include dipeptides, tripeptides, and tetrapeptides. A ...

that selectively inhibits Kv1.3 voltage-dependent

potassium channels Potassium channels are the most widely distributed type of ion channel found in virtually all organisms. They form potassium-selective pores that span cell membranes. Potassium channels are found in most cell types and control a wide variety of cel ...

. It is found in the venom of ''

Centruroides margaritatus ''Centruroides'' is a genus of scorpions of the family Buthidae. Several North American species are known by the common vernacular name bark scorpion. Numerous species are extensively found throughout the southern United States, Mexico, Centr ...

'', also known as the Central American Bark Scorpion. Margatoxin was first discovered in 1993. It was purified from

scorpion Scorpions are predatory arachnids of the order Scorpiones. They have eight legs, and are easily recognized by a pair of grasping pincers and a narrow, segmented tail, often carried in a characteristic forward curve over the back and always end ...

venom and its

amino acid Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although hundreds of amino acids exist in nature, by far the most important are the alpha-amino acids, which comprise proteins. Only 22 alpha am ...

sequence was determined.

Structure

Margatoxin is a

of 39

amino acids Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although hundreds of amino acids exist in nature, by far the most important are the alpha-amino acids, which comprise proteins. Only 22 alpha am ...

with a

molecular weight A molecule is a group of two or more atoms held together by attractive forces known as chemical bonds; depending on context, the term may or may not include ions which satisfy this criterion. In quantum physics, organic chemistry, and bioch ...

of 4185 Dalton. The primary

sequence of margatoxin is as follows: : Thr-Ile-Ile-Asn-Val-Lys-Cys-Thr-Ser-Pro-Lys-Gln-Cys-Leu-Pro-Pro-Cys-Lys-Ala-Gln-Phe-Gly-Gln-Ser-Ala-Gly-Ala-Lys-Cys-Met-Asn-Gly-Lys-Cys-Lys-Cys-Tyr-Pro-His Or, when translated to one-letter sequence, :TIINVKCTSPKQCLPPCKAQFGQSAGAKCMNGKCKCYPH. There are

disulfide bridge In biochemistry, a disulfide (or disulphide in British English) refers to a functional group with the structure . The linkage is also called an SS-bond or sometimes a disulfide bridge and is usually derived by the coupling of two thiol groups. In ...

s between Cys7-Cys29, Cys13-Cys34 and Cys17-Cys36.
Margatoxin is classified as a "scorpion short toxin" by

Pfam Pfam is a database of protein families that includes their annotations and multiple sequence alignments generated using hidden Markov models. The most recent version, Pfam 35.0, was released in November 2021 and contains 19,632 families. Uses ...

, showing sequence homology with other potassium channel blockers, such as

charybdotoxin Charybdotoxin (CTX) is a 37 amino acid neurotoxin from the venom of the scorpion '' Leiurus quinquestriatus hebraeus'' (''deathstalker'') that blocks calcium-activated potassium channels. This blockade causes hyperexcitability of the nervous syst ...

(44%),

kaliotoxin {, style="float: right; clear: right; margin: 0 0 0.5em 1em; background: #ffffff;" class="toccolours" border="0" cellpadding="1" align="right" width="280" !The amino acid sequence of Kaliotoxin , - , bgcolor="#eeeeee" , N - Gly - Val - Glu - Ile ...

(54%),

iberiotoxin Iberiotoxin (IbTX) is an ion channel toxin purified from the Eastern Indian red scorpion ''Hottentotta tamulus''. Iberiotoxin selectively inhibits the current through large-conductance calcium-activated potassium channels. Chemistry Iberiotoxin ...

(41%) and noxiustoxin (79%), which are also derived from scorpion venom.

Synthesis

Margatoxin is a

originally purified from the venom of the

''Centrutoides margaritatus'' (Central American Bark Scorpion). Scorpion toxins are specific and have a high

affinity Affinity may refer to: Commerce, finance and law * Affinity (law), kinship by marriage * Affinity analysis, a market research and business management technique * Affinity Credit Union, a Saskatchewan-based credit union * Affinity Equity Par ...

for their targets, and this makes them good tools to characterize various

receptor Receptor may refer to: * Sensory receptor, in physiology, any structure which, on receiving environmental stimuli, produces an informative nerve impulse *Receptor (biochemistry), in biochemistry, a protein molecule that receives and responds to a ...

proteins involved in

ion channel Ion channels are pore-forming membrane proteins that allow ions to pass through the channel pore. Their functions include establishing a resting membrane potential, shaping action potentials and other electrical signals by gating the flow of io ...

functioning. Because only low amounts of natural toxins can be isolated from

venoms, a chemical synthesis approach has been utilised to produce sufficient protein for research. This approach is not only produces enough material to study the effects on

but ensures purity as toxin isolated from the scorpion venom risks contamination by other active compounds.
Margatoxin can be chemically synthesized using the

solid phase synthesis In chemistry, solid-phase synthesis is a method in which molecules are covalently bound on a solid support material and synthesised step-by-step in a single reaction vessel utilising selective protecting group chemistry. Benefits compared with n ...

technique. The compound gained by this technique was compared with the natural, purified margatoxin. Both compounds had the same physical and biological properties. The chemically synthesized margatoxin is now used to study the role of Kv1.3 channels.

Mechanism of action

Margatoxin blocks

Kv1.1 Kv1.2 en Kv1.3. Kv1.2 channel regulates

neurotransmitter A neurotransmitter is a signaling molecule secreted by a neuron to affect another cell across a synapse. The cell receiving the signal, any main body part or target cell, may be another neuron, but could also be a gland or muscle cell. Neuro ...

release associated with heart rate,

insulin Insulin (, from Latin ''insula'', 'island') is a peptide hormone produced by beta cells of the pancreatic islets encoded in humans by the ''INS'' gene. It is considered to be the main anabolic hormone of the body. It regulates the metabolism o ...

secretion,

neuronal A neuron, neurone, or nerve cell is an electrically excitable cell that communicates with other cells via specialized connections called synapses. The neuron is the main component of nervous tissue in all animals except sponges and placozoa. No ...

excitability,

epithelial Epithelium or epithelial tissue is one of the four basic types of animal tissue, along with connective tissue, muscle tissue and nervous tissue. It is a thin, continuous, protective layer of compactly packed cells with a little intercellula ...

electrolyte An electrolyte is a medium containing ions that is electrically conducting through the movement of those ions, but not conducting electrons. This includes most soluble salts, acids, and bases dissolved in a polar solvent, such as water. Upon dis ...

transport,

smooth muscle Smooth muscle is an involuntary non-striated muscle, so-called because it has no sarcomeres and therefore no striations (''bands'' or ''stripes''). It is divided into two subgroups, single-unit and multiunit smooth muscle. Within single-unit mus ...

contraction,

immunological response An immune response is a reaction which occurs within an organism for the purpose of defending against foreign invaders. These invaders include a wide variety of different microorganisms including viruses, bacteria, parasites, and fungi which could ...

and cell volume. Kv1.3 channels are expressed in T and B

lymphocytes A lymphocyte is a type of white blood cell (leukocyte) in the immune system of most vertebrates. Lymphocytes include natural killer cells (which function in cell-mediated, cytotoxic innate immunity), T cells (for cell-mediated, cytotoxic adap ...

. Margatoxin irreversibly inhibits the proliferation of human T-cells in a concentration of 20 μM. At lower concentrations, this inhibition is reversible.

Influence on cardiovascular function

Margatoxin significantly reduces outward currents of Kv1.3 channels and depolarized resting

membrane potential Membrane potential (also transmembrane potential or membrane voltage) is the difference in electric potential between the interior and the exterior of a biological cell. That is, there is a difference in the energy required for electric charges ...

. It increases the time necessary to conduct

action potentials An action potential occurs when the membrane potential of a specific cell location rapidly rises and falls. This depolarization then causes adjacent locations to similarly depolarize. Action potentials occur in several types of animal cells, c ...

in the cell in response to a stimulus.

Acetylcholine Acetylcholine (ACh) is an organic chemical that functions in the brain and body of many types of animals (including humans) as a neurotransmitter. Its name is derived from its chemical structure: it is an ester of acetic acid and choline. Part ...

(ACh) plays a key role in activation of

nicotinic Nicotinic acetylcholine receptors, or nAChRs, are receptor polypeptides that respond to the neurotransmitter acetylcholine. Nicotinic receptors also respond to drugs such as the agonist nicotine. They are found in the central and peripheral ner ...

and

muscarinic Muscarinic acetylcholine receptors, or mAChRs, are acetylcholine receptors that form G protein-coupled receptor complexes in the cell membranes of certain neurons and other cells. They play several roles, including acting as the main end-rec ...

ACh-receptors. Margatoxin influences

ACh-receptor

agonist An agonist is a chemical that activates a receptor to produce a biological response. Receptors are cellular proteins whose activation causes the cell to modify what it is currently doing. In contrast, an antagonist blocks the action of the ago ...

-induced

norepinephrine Norepinephrine (NE), also called noradrenaline (NA) or noradrenalin, is an organic chemical in the catecholamine family that functions in the brain and body as both a hormone and neurotransmitter. The name "noradrenaline" (from Latin '' ad'', ...

release. Upon activation of

ACh receptors with bethanechol, margatoxin-sensitive current was suppressed. Therefore, it was concluded that Kv1.3 affects the function of postganglionic

sympathetic neuron The sympathetic nervous system (SNS) is one of the three divisions of the autonomic nervous system, the others being the parasympathetic nervous system and the enteric nervous system. The enteric nervous system is sometimes considered part of t ...

s, so one could suggest that Kv1.3 influences sympathetic control of cardiovascular function.

Immune system suppression

Kv1.3-channels can be found in various cells, including T-

and

macrophages Macrophages (abbreviated as M φ, MΦ or MP) ( el, large eaters, from Greek ''μακρός'' (') = large, ''φαγεῖν'' (') = to eat) are a type of white blood cell of the immune system that engulfs and digests pathogens, such as cancer ce ...

. To activate an

immune response An immune response is a reaction which occurs within an organism for the purpose of defending against foreign invaders. These invaders include a wide variety of different microorganisms including viruses, bacteria, parasites, and fungi which could ...

a T-

lymphocyte A lymphocyte is a type of white blood cell (leukocyte) in the immune system of most vertebrates. Lymphocytes include natural killer cells (which function in cell-mediated, cytotoxic innate immunity), T cells (for cell-mediated, cytotoxic ad ...

has to come into contact with a

macrophage Macrophages (abbreviated as M φ, MΦ or MP) ( el, large eaters, from Greek ''μακρός'' (') = large, ''φαγεῖν'' (') = to eat) are a type of white blood cell of the immune system that engulfs and digests pathogens, such as cancer cel ...

. The

can then produce

cytokines Cytokines are a broad and loose category of small proteins (~5–25 kDa) important in cell signaling. Cytokines are peptides and cannot cross the lipid bilayer of cells to enter the cytoplasm. Cytokines have been shown to be involved in autocrin ...

, such as IL-1, IL-6, and TNF-α.

Cytokines Cytokines are a broad and loose category of small proteins (~5–25 kDa) important in cell signaling. Cytokines are peptides and cannot cross the lipid bilayer of cells to enter the cytoplasm. Cytokines have been shown to be involved in autocrin ...

are cell signaling molecules that can enhance the

. Kv1.3-channels are important for the activation of T-

, and thus for the activation of

. The disturbance of the function of Kv1.3-channels, for example due to inhibition of these channels, will lower the

production and

proliferation in vitro. This would lead to

suppression ''in vivo''. Kv channels are regulated during proliferation and regulation of

and their activity is important during cell responses. In contrast to

leukocytes White blood cells, also called leukocytes or leucocytes, are the cells of the immune system that are involved in protecting the body against both infectious disease and foreign invaders. All white blood cells are produced and derived from mult ...

which have monomeric Kv1.3 channels,

have heterotetrameric Kv1.3/Kv1.5 channels. These heterotetramers plays a role in regulating the

on different stages of

activation by

Potassium channels Potassium channels are the most widely distributed type of ion channel found in virtually all organisms. They form potassium-selective pores that span cell membranes. Potassium channels are found in most cell types and control a wide variety of cel ...

are involved in

leukocyte White blood cells, also called leukocytes or leucocytes, are the cells of the immune system that are involved in protecting the body against both infectious disease and foreign invaders. All white blood cells are produced and derived from mult ...

activation by calcium. The possible different conformations of these Kv1.3 and 1.5 complexes can affect the

. Margatoxin inhibits Kv1.3 channels, so no heterodimers can be formed. The effect of margatoxin is similar to the effect of DEX. DEX diminishes amount of K1.3 channels by binding to GC

, which leads to downregulating of expression of K1.3 channels. Both margatoxin and DEX lead to immune suppression.

Effects on ion channels in lymphocytes

Ion channels Ion channels are pore-forming membrane proteins that allow ions to pass through the channel pore. Their functions include establishing a resting membrane potential, shaping action potentials and other electrical signals by gating the flow of io ...

play a key role in

signal transduction.

are required for the activation of T-cells. Pharmacological inhibition of

can be useful in the treatment of immune diseases. The

exerts powerful effects on the

activation. The resting potential results primarily from a potassium-diffusion potential contributed by

. Margatoxin depolarizes resting human T cells. Pharmacological studies suggest that functional

are required in the activation of T- and B-cells. KV channel blockers inhibit activation, gene expression, killing by cytotoxic T cells and NK cells,

lymphokine Lymphokines are a subset of cytokines that are produced by a type of immune cell known as a lymphocyte. They are protein mediators typically produced by T cells to direct the immune system response by signaling between its cells. Lymphokines have ...

secretion and proliferation. Margatoxin blocks

mitogen A mitogen is a small bioactive protein or peptide that induces a cell to begin cell division, or enhances the rate of division (mitosis). Mitogenesis is the induction (triggering) of mitosis, typically via a mitogen. The mechanism of action of a ...

-induced proliferation, the mixed

response and the secretion of Interleukin-2 and interferon-gamma (IFN-γ). This provides the strongest available evidence for a role of KV channels in mitogenesis.

Toxicity

Margatoxin can have several different effects on the body:Material Safety Data Sheet, Margatoxin: sc-3586, Santa Cruz Biotechnology, 2004 * May cause skin irritation * May be harmful if absorbed through the skin * May cause eye irritation * May be harmful if inhaled * Material may be irritating to mucous membranes and upper respiratory tract * May be harmful if swallowed * Prolonged or repeated exposure may cause allergic reactions in certain sensitive individuals * May be fatal if enters bloodstream The chronic effects target the heart, nerves, lungs, skeleton and muscles. The

median lethal dose In toxicology, the median lethal dose, LD50 (abbreviation for "lethal dose, 50%"), LC50 (lethal concentration, 50%) or LCt50 is a toxic unit that measures the lethal dose of a toxin, radiation, or pathogen. The value of LD50 for a substance is the ...

(LD50) of margatoxin is 59.9 mg/kg, so ''Centruroides margaritatus'' stings are not dangerous to humans except as a result of possible

anaphylactic Anaphylaxis is a serious, potentially fatal allergic reaction and medical emergency that is rapid in onset and requires immediate medical attention regardless of use of emergency medication on site. It typically causes more than one of the follow ...

responses. They do cause pain, local swelling, and tingling for 3–4 hours, but no intervention beyond symptomatic relief should be necessary.

Effects on animals

Margatoxin leads to the

depolarization In biology, depolarization or hypopolarization is a change within a cell, during which the cell undergoes a shift in electric charge distribution, resulting in less negative charge inside the cell compared to the outside. Depolarization is esse ...

of human and pig cells ''in vitro''. By blocking 99% of the KV1.3-channels, margatoxin inhibits the proliferation response of T-cells in mini-swine. Furthermore, it suppresses a B-cell response to

allogenic In ecology, allogenic succession is succession driven by the abiotic components of an ecosystem. In contrast, autogenic succession is driven by the biotic components of the ecosystem. An allogenic succession can be brought about in a number of ways ...

immunization Immunization, or immunisation, is the process by which an individual's immune system becomes fortified against an infectious agent (known as the immunogen). When this system is exposed to molecules that are foreign to the body, called ''non-sel ...

and inhibits the delayed-type hypersensitivity reaction to tuberculin. In pigs, the protein's

half-life Half-life (symbol ) is the time required for a quantity (of substance) to reduce to half of its initial value. The term is commonly used in nuclear physics to describe how quickly unstable atoms undergo radioactive decay or how long stable ato ...

is two hours. When the

is continuously infused, it leads to diarrhea and hypersalivation. However, no major toxic effects are observed in animals. In contrast to when the plasma concentration of margatoxin is higher than 10nM, the transient hyperactivity occurs in pigs. It might be an effect of Kv1.1 and Kv1.2 channels in the brain.

Efficacy and side effects

Kv1.3 is already linked with proliferation of

, vascular smooth cells,

oligodendrocytes Oligodendrocytes (), or oligodendroglia, are a type of neuroglia whose main functions are to provide support and insulation to axons in the central nervous system of jawed vertebrates, equivalent to the function performed by Schwann cells in the ...

and cancer cells. Recent studies have shown that there is therapeutical potential for Kv1.3-blockers such as Margatoxin. In a minipig treatment a study with margatoxin has been conducted. An eight-day treatment led to a prolonged immune suppression that lasted three to four weeks after termination of dosing. Thymic atrophy (reduced thymus) was observed. Especially the cells in the cortical region had decreased in number

Medicinal significance

Neointimal Hyperplasia is the movement and proliferation of

cells into the luminal area of a blood vessel. This generates a new inner structure that can block blood flow. This is commonly seen to cause failure of interventional clinical procedures that include placement of stents and bypass grafts. Due to changes in

potassium channel Potassium channels are the most widely distributed type of ion channel found in virtually all organisms. They form potassium-selective pores that span cell membranes. Potassium channels are found in most cell types and control a wide variety of cel ...

type the vascular

cells switch from the contractile to proliferating phenotype. It is suggested that Kv1.3 is important in proliferating vascular

cells. Inhibitors of such channels suppress vascular

proliferation,

stenosis A stenosis (from Ancient Greek στενός, "narrow") is an abnormal narrowing in a blood vessel or other tubular organ or structure such as foramina and canals. It is also sometimes called a stricture (as in urethral stricture). ''Stricture'' ...

following injury, and neointimal hyperplasia. Studies shows that margatoxin is a high potency inhibitor of vascular cell migration, with an IC50 (half maximal inhibitory concentration) of 85 pM. In this study, a negative effect was also found. There have been vasoconstrictor effects observed in some arteries, but elevated blood pressure has not appeared as a significant concern.