Micrurus tener tener Kunitz-type neurotoxin MitTx-alpha
Micrurus tener tener Kunitz-type neurotoxin MitTx-alpha is a subunit of the pain-inducing, heterodimeric polypeptide toxin that activates acid sensing ion channel a (ASIC1a) at nanomolar concentrations in a pH-independent manner. Acid sensing ion channels (ASICs) are sodium-selective, voltage-independent and amiloride-blockable ion channels that detect extracellular protons produced during inflammation or ischemic injury, and belong to the superfamily of degenerin/epithelial sodium channels. Subtype ASICa is expressed by primary afferent sensory neurons and is activated by MitTx. MitTx consists of two, non-covalently associated alpha and beta subunits that resemble Kunitz and phospholipase-A2 proteins, respectively, and together they function as a potent and selective ASIC1a agonist. The MitTx-alpha structures is similar to those of Kunitz-type proteinase inhibitors such as BPTI (bovine pancreatic trypsin inhibitor), showing an alpha/beta fold with irregular secondary structure stabilized by three disulfide bonds.
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