A new sea anemone peptide, APETx2, inhibits ASIC3, a major acid-sensitive channel in sensory neurons

Abstract

From a systematic screening of animal venoms, we isolated a new toxin (APETx2) from the sea anemone Anthopleura elegantissima, which inhibits ASIC3 homomeric channels and ASIC3-containing heteromeric channels both in heterologous expression systems and in primary cultures of rat sensory neurons. APETx2 is a 42 amino-acid peptide crosslinked by three disulfide bridges, with a structural organization similar to that of other sea anemone toxins that inhibit voltage-sensitive Na þ and K þ channels. APETx2 reversibly inhibits rat ASIC3(IC 50 ¼ 63 nM), without any effect on ASIC1a, ASIC1b, and ASIC2a. APETx2 directly inhibits the ASIC3 channel by acting at its external side, and it does not modify the channel unitary conductance. APETx2 also inhibits heteromeric ASIC2b þ 3 current (IC 50 ¼117 nM), while it has less affinity for ASIC1b þ 3 (IC 50 ¼ 0.9 lM), ASIC1a þ 3 (IC 50 ¼ 2 lM), and no effect on the ASIC2a þ 3 current. The ASIC3-like current in primary cultured sensory neurons is partly and reversibly inhibited by APETx2 with an IC 50 of 216 nM, probably due to the mixed inhibitions of various co-expressed ASIC3-containing channels.

Acid-sensing ion channels (ASICs) as pharmacological targets for neurodegenerative diseases

“…Homomeric ASIC1a, ASIC1b, ASIC2a, and heteromeric ASIC3/2a channels, on the other hand, are not sensitive to APETx2. Similar to PcTX1, APETx2 is cross-linked by three disulfide bonds (Figure 3) [61]. However, it does not show any sequence homologies with PcTX1.…”

“…It is a potent and selective inhibitor for homomeric ASIC3 and ASIC3 containing channels [61]. It reduces transient peak acid-evoked currents mediated by homomeric ASIC3 channels in heterologous expression systems and in primary cultures of sensory neurons [61].…”

Binding Site and Inhibitory Mechanism of the Mambalgin-2 Pain-relieving Peptide on Acid-sensing Ion Channel 1a

“…The MitTx identified from the venom of the Texas coral snake does not inhibit but potently activates several homomeric and heteromeric ASIC channels and helped to identify a role for peripheral ASIC1a-containing channels in cutaneous pain (13) and to define the structure of the open state of ASIC1a (14). The sea anemone toxin APETx2, a peptide that blocks ASIC3-containing channels (15) and inhibits to some extent Nav1.8 voltage-dependent Na ϩ channels (16,17), has been used to demonstrate the role of peripheral ASIC3-containing channels in acidic, inflammatory, and postoperative pain (18 -20).…”

Ion Channels as Drug Targets in Central Nervous System Disorders

“…APETx2 is a basic peptide (pI = 9.59) of 42 amino acids, cross-linked by three disulfide bridges. The discovery of a toxin with ASIC3-blocking activity is of major significance given the substantial amount of evidence now implicating this channel in the transduction of acidinduced pain and hyperalgesia [303].…”