Margatoxin
Encyclopedia
Margatoxin is a peptide
that selectively inhibits Kv1.3 voltage-dependent potassium channels. It is found in the venom of Centruroides margaritatus, also known as the Central American Bark Scorpion. Margatoxin was first discovered in 1993. It was purified from scorpion
venom and it's amino acid
sequence was determined.
of 39 amino acids with a molecular weight of 4185 Dalton. The primary amino acid
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.
There are disulfide bridges between Cys 7-Cys29, Cys13-Cys34 and Cys17-Cys36.
Margatoxin shows sequence homology with other potassium channel blockers, such as charybdotoxin (44%), kaliotoxin (54%), iberiotoxin (41%) and noxiustoxin (79%), which are also derived from scorpion venom.
purified from the venom of the scorpion
Centrutoides Margaritatus. Scorpion toxins are specific and have a high affinity, and this makes them good tools to characterize various receptor
proteins involved in ion channel
functioning. Because only low amounts of natural toxins can be isolated from scorpion
venoms, a chemical synthesis approach was needed. This approach is necessary to study the effects on the potassium channels and is sometimes safer because a natural toxin isolated from the scorpion venom risks contamination by other active compounds.
Margatoxin can be chemically synthesized using the solid phase synthesis 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.
Kv1.2 channel regulates neurotransmitter
release associated with heart rate, insulin
secretion, neuronal excitability, epithelial electrolyte
transport, smooth muscle
contraction, immunological response and cell volume. Kv1.3 channels are expressed in T and B lymphocytes.
Margatoxin irreversibly inhibits the proliferation of human T-cells in a concentration of 20 μM. At lower concentrations, this inhibition is reversible.
. It increases the time necessary to conduct action potentials in the cell in response to the stimulus. Acetylcholine
(ACh) plays a key role in activation of nicotinic and muscarinic ACh-receptors. Margatoxin influences nicotinic ACh-receptor agonist
-induced norepinephrine
release. Upon activation of muscarinic ACh receptors with bethanechol, Margatoxin-sensitive current was suppressed. Therefore it was concluded that Kv1.3 affects the function of postganglionic sympathetic neurons, so one could suggest that Kv1.3 influences sympathetic control of cardiovascular function.
has to come into contact with an macrophage
. The macrophage
can then produce cytokines, such as IL-1, IL-6, and TNF-α. Cytokines are cell signaling molecules that can enhance the immune response. Kv1.3-channels are important for the activation of T-lymphocytes, and thus for the activation of macrophages. The disturbance of the function of Kv1.3-channels, for example due to inhibition of these channels, will lower the cytokines production and lymphocyte
proliferation in vitro. This would lead to immune response suppression in vivo.
Kv channels are regulated during proliferation and regulation of macrophages and their activity is important during cell responses. In contrast to leukocytes which have monomeric Kv1.3 channels, macrophages have heterotetrameric Kv1.3/Kv1.5 channels. These heterotetramers plays a role in regulating the membrane potential
of macrophages on different stages of macrophage
activation by lymphocytes. Potassium channels are involved in leukocyte activation by calcium. The possible different conformations of these Kv1.3 and 1.5 complexes can affect the immune response. 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 receptor
, which leads to downregulating of expression of K1.3 channels. Both margatoxin and DEX lead to immune suppression.
signal transduction. Potassium channels are required for the activation of T-cells. Pharmacological inhibition of Potassium channels can be useful in the treatment of immune diseases. The membrane potential
exerts powerful effects on the lymphocyte
activation. The resting potential results primarily from a potassium-diffusion potential contributed by potassium channels. Margatoxin depolarizes resting human T cells. Pharmacological studies suggest that functional potassium channels 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
secretion and proliferation. Margatoxin blocks mitogen
-induced proliferation, the mixed lymphocyte
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.
The chronic effects include the following target organs: heart, nerves, lungs, skeleton and muscles.
The median lethal dose (LD50) of margatoxin is 59.9 mg/kg, so Centruroides margaritatus stings are not dangerous to humans except as a result of possible anaphylactic responses. They do cause pain, local swelling and tingling for 3–4 hours, but no intervention beyond symptomatic relief should be necessary.
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 immunization
and inhibits the delayed-type hypersensitivity reaction to tuberculin. In pigs, the protein’s half-life
is two hours. When the peptide
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.
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
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
type the vascular smooth muscle
cells switch from the contractile to proliferating phenotype. It is suggested that Kv1.3 is important in proliferating vascular smooth muscle
cells. Inhibitors of such channels suppress vascular smooth muscle
proliferation, stenosis
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.
Peptide
Peptides are short polymers of amino acid monomers linked by peptide bonds. They are distinguished from proteins on the basis of size, typically containing less than 50 monomer units. The shortest peptides are dipeptides, consisting of two amino acids joined by a single peptide bond...
that selectively inhibits Kv1.3 voltage-dependent potassium channels. It is found in the venom of Centruroides margaritatus, also known as the Central American Bark Scorpion. Margatoxin was first discovered in 1993. It was purified from scorpion
Scorpion
Scorpions are predatory arthropod animals of the order Scorpiones within the class Arachnida. They have eight legs and are easily recognized by the pair of grasping claws and the narrow, segmented tail, often carried in a characteristic forward curve over the back, ending with a venomous stinger...
venom and it's amino acid
Amino acid
Amino acids are molecules containing an amine group, a carboxylic acid group and a side-chain that varies between different amino acids. The key elements of an amino acid are carbon, hydrogen, oxygen, and nitrogen...
sequence was determined.
Structure
Margatoxin is a peptidePeptide
Peptides are short polymers of amino acid monomers linked by peptide bonds. They are distinguished from proteins on the basis of size, typically containing less than 50 monomer units. The shortest peptides are dipeptides, consisting of two amino acids joined by a single peptide bond...
of 39 amino acids with a molecular weight of 4185 Dalton. The primary amino acid
Amino acid
Amino acids are molecules containing an amine group, a carboxylic acid group and a side-chain that varies between different amino acids. The key elements of an amino acid are carbon, hydrogen, oxygen, and nitrogen...
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.
There are disulfide bridges between Cys 7-Cys29, Cys13-Cys34 and Cys17-Cys36.
Margatoxin shows sequence homology with other potassium channel blockers, such as charybdotoxin (44%), kaliotoxin (54%), iberiotoxin (41%) and noxiustoxin (79%), which are also derived from scorpion venom.
Synthesis
Margatoxin is originally a peptidePeptide
Peptides are short polymers of amino acid monomers linked by peptide bonds. They are distinguished from proteins on the basis of size, typically containing less than 50 monomer units. The shortest peptides are dipeptides, consisting of two amino acids joined by a single peptide bond...
purified from the venom of the scorpion
Scorpion
Scorpions are predatory arthropod animals of the order Scorpiones within the class Arachnida. They have eight legs and are easily recognized by the pair of grasping claws and the narrow, segmented tail, often carried in a characteristic forward curve over the back, ending with a venomous stinger...
Centrutoides Margaritatus. Scorpion toxins are specific and have a high affinity, and this makes them good tools to characterize various receptor
Receptor (biochemistry)
In biochemistry, a receptor is a molecule found on the surface of a cell, which receives specific chemical signals from neighbouring cells or the wider environment within an organism...
proteins involved in ion channel
Ion channel
Ion channels are pore-forming proteins that help establish and control the small voltage gradient across the plasma membrane of cells by allowing the flow of ions down their electrochemical gradient. They are present in the membranes that surround all biological cells...
functioning. Because only low amounts of natural toxins can be isolated from scorpion
Scorpion
Scorpions are predatory arthropod animals of the order Scorpiones within the class Arachnida. They have eight legs and are easily recognized by the pair of grasping claws and the narrow, segmented tail, often carried in a characteristic forward curve over the back, ending with a venomous stinger...
venoms, a chemical synthesis approach was needed. This approach is necessary to study the effects on the potassium channels and is sometimes safer because a natural toxin isolated from the scorpion venom risks contamination by other active compounds.
Margatoxin can be chemically synthesized using the solid phase synthesis 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 potassium channels Kv1.1 Kv1.2 en Kv1.3.Kv1.2 channel regulates neurotransmitter
Neurotransmitter
Neurotransmitters are endogenous chemicals that transmit signals from a neuron to a target cell across a synapse. Neurotransmitters are packaged into synaptic vesicles clustered beneath the membrane on the presynaptic side of a synapse, and are released into the synaptic cleft, where they bind to...
release associated with heart rate, insulin
Insulin
Insulin is a hormone central to regulating carbohydrate and fat metabolism in the body. Insulin causes cells in the liver, muscle, and fat tissue to take up glucose from the blood, storing it as glycogen in the liver and muscle....
secretion, neuronal excitability, epithelial electrolyte
Electrolyte
In chemistry, an electrolyte is any substance containing free ions that make the substance electrically conductive. The most typical electrolyte is an ionic solution, but molten electrolytes and solid electrolytes are also possible....
transport, smooth muscle
Smooth muscle
Smooth muscle is an involuntary non-striated muscle. It is divided into two sub-groups; the single-unit and multiunit smooth muscle. Within single-unit smooth muscle tissues, the autonomic nervous system innervates a single cell within a sheet or bundle and the action potential is propagated by...
contraction, immunological response and cell volume. Kv1.3 channels are expressed in T and B lymphocytes.
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 potentialMembrane potential
Membrane potential is the difference in electrical potential between the interior and exterior of a biological cell. All animal cells are surrounded by a plasma membrane composed of a lipid bilayer with a variety of types of proteins embedded in it...
. It increases the time necessary to conduct action potentials in the cell in response to the stimulus. Acetylcholine
Acetylcholine
The chemical compound acetylcholine is a neurotransmitter in both the peripheral nervous system and central nervous system in many organisms including humans...
(ACh) plays a key role in activation of nicotinic and muscarinic ACh-receptors. Margatoxin influences nicotinic ACh-receptor agonist
Agonist
An agonist is a chemical that binds to a receptor of a cell and triggers a response by that cell. Agonists often mimic the action of a naturally occurring substance...
-induced norepinephrine
Norepinephrine
Norepinephrine is the US name for noradrenaline , a catecholamine with multiple roles including as a hormone and a neurotransmitter...
release. Upon activation of muscarinic ACh receptors with bethanechol, Margatoxin-sensitive current was suppressed. Therefore it was concluded that Kv1.3 affects the function of postganglionic sympathetic neurons, 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-lymphocytes and macrophages. To activate an immune response an T-lymphocyteLymphocyte
A lymphocyte is a type of white blood cell in the vertebrate immune system.Under the microscope, lymphocytes can be divided into large lymphocytes and small lymphocytes. Large granular lymphocytes include natural killer cells...
has to come into contact with an macrophage
Macrophage
Macrophages are cells produced by the differentiation of monocytes in tissues. Human macrophages are about in diameter. Monocytes and macrophages are phagocytes. Macrophages function in both non-specific defense as well as help initiate specific defense mechanisms of vertebrate animals...
. The macrophage
Macrophage
Macrophages are cells produced by the differentiation of monocytes in tissues. Human macrophages are about in diameter. Monocytes and macrophages are phagocytes. Macrophages function in both non-specific defense as well as help initiate specific defense mechanisms of vertebrate animals...
can then produce cytokines, such as IL-1, IL-6, and TNF-α. Cytokines are cell signaling molecules that can enhance the immune response. Kv1.3-channels are important for the activation of T-lymphocytes, and thus for the activation of macrophages. The disturbance of the function of Kv1.3-channels, for example due to inhibition of these channels, will lower the cytokines production and lymphocyte
Lymphocyte
A lymphocyte is a type of white blood cell in the vertebrate immune system.Under the microscope, lymphocytes can be divided into large lymphocytes and small lymphocytes. Large granular lymphocytes include natural killer cells...
proliferation in vitro. This would lead to immune response suppression in vivo.
Kv channels are regulated during proliferation and regulation of macrophages and their activity is important during cell responses. In contrast to leukocytes which have monomeric Kv1.3 channels, macrophages have heterotetrameric Kv1.3/Kv1.5 channels. These heterotetramers plays a role in regulating the membrane potential
Membrane potential
Membrane potential is the difference in electrical potential between the interior and exterior of a biological cell. All animal cells are surrounded by a plasma membrane composed of a lipid bilayer with a variety of types of proteins embedded in it...
of macrophages on different stages of macrophage
Macrophage
Macrophages are cells produced by the differentiation of monocytes in tissues. Human macrophages are about in diameter. Monocytes and macrophages are phagocytes. Macrophages function in both non-specific defense as well as help initiate specific defense mechanisms of vertebrate animals...
activation by lymphocytes. Potassium channels are involved in leukocyte activation by calcium. The possible different conformations of these Kv1.3 and 1.5 complexes can affect the immune response. 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 receptor
Receptor (biochemistry)
In biochemistry, a receptor is a molecule found on the surface of a cell, which receives specific chemical signals from neighbouring cells or the wider environment within an organism...
, 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 play a key role in lymphocyteLymphocyte
A lymphocyte is a type of white blood cell in the vertebrate immune system.Under the microscope, lymphocytes can be divided into large lymphocytes and small lymphocytes. Large granular lymphocytes include natural killer cells...
signal transduction. Potassium channels are required for the activation of T-cells. Pharmacological inhibition of Potassium channels can be useful in the treatment of immune diseases. The membrane potential
Membrane potential
Membrane potential is the difference in electrical potential between the interior and exterior of a biological cell. All animal cells are surrounded by a plasma membrane composed of a lipid bilayer with a variety of types of proteins embedded in it...
exerts powerful effects on the lymphocyte
Lymphocyte
A lymphocyte is a type of white blood cell in the vertebrate immune system.Under the microscope, lymphocytes can be divided into large lymphocytes and small lymphocytes. Large granular lymphocytes include natural killer cells...
activation. The resting potential results primarily from a potassium-diffusion potential contributed by potassium channels. Margatoxin depolarizes resting human T cells. Pharmacological studies suggest that functional potassium channels 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
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 signalling between its cells...
secretion and proliferation. Margatoxin blocks mitogen
Mitogen
A mitogen is a chemical substance that encourages a cell to commence cell division, triggering mitosis. A mitogen is usually some form of a protein.Mitogenesis is the induction of mitosis, typically via a mitogen....
-induced proliferation, the mixed lymphocyte
Lymphocyte
A lymphocyte is a type of white blood cell in the vertebrate immune system.Under the microscope, lymphocytes can be divided into large lymphocytes and small lymphocytes. Large granular lymphocytes include natural killer cells...
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. These are listed below.| Acute effects |
|---|
| 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 include the following target organs: heart, nerves, lungs, skeleton and muscles.
The median lethal dose (LD50) of margatoxin is 59.9 mg/kg, so Centruroides margaritatus stings are not dangerous to humans except as a result of possible anaphylactic 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 depolarizationDepolarization
In biology, depolarization is a change in a cell's membrane potential, making it more positive, or less negative. In neurons and some other cells, a large enough depolarization may result in an action potential...
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 immunization
Immunization
Immunization, or immunisation, is the process by which an individual's immune system becomes fortified against an agent ....
and inhibits the delayed-type hypersensitivity reaction to tuberculin. In pigs, the protein’s half-life
Half-life
Half-life, abbreviated t½, is the period of time it takes for the amount of a substance undergoing decay to decrease by half. The name was originally used to describe a characteristic of unstable atoms , but it may apply to any quantity which follows a set-rate decay.The original term, dating to...
is two hours. When the peptide
Peptide
Peptides are short polymers of amino acid monomers linked by peptide bonds. They are distinguished from proteins on the basis of size, typically containing less than 50 monomer units. The shortest peptides are dipeptides, consisting of two amino acids joined by a single peptide bond...
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 lymphocytes, vascular smooth cells, oligodendrocytes 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 smooth muscleSmooth muscle
Smooth muscle is an involuntary non-striated muscle. It is divided into two sub-groups; the single-unit and multiunit smooth muscle. Within single-unit smooth muscle tissues, the autonomic nervous system innervates a single cell within a sheet or bundle and the action potential is propagated by...
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 channel
In the field of cell biology, potassium channels are the most widely distributed type of ion channel and are found in virtually all living organisms. They form potassium-selective pores that span cell membranes...
type the vascular smooth muscle
Smooth muscle
Smooth muscle is an involuntary non-striated muscle. It is divided into two sub-groups; the single-unit and multiunit smooth muscle. Within single-unit smooth muscle tissues, the autonomic nervous system innervates a single cell within a sheet or bundle and the action potential is propagated by...
cells switch from the contractile to proliferating phenotype. It is suggested that Kv1.3 is important in proliferating vascular smooth muscle
Smooth muscle
Smooth muscle is an involuntary non-striated muscle. It is divided into two sub-groups; the single-unit and multiunit smooth muscle. Within single-unit smooth muscle tissues, the autonomic nervous system innervates a single cell within a sheet or bundle and the action potential is propagated by...
cells. Inhibitors of such channels suppress vascular smooth muscle
Smooth muscle
Smooth muscle is an involuntary non-striated muscle. It is divided into two sub-groups; the single-unit and multiunit smooth muscle. Within single-unit smooth muscle tissues, the autonomic nervous system innervates a single cell within a sheet or bundle and the action potential is propagated by...
proliferation, stenosis
Stenosis
A stenosis is an abnormal narrowing in a blood vessel or other tubular organ or structure.It is also sometimes called a 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.