Draft:Π-Theraphotoxin-Hm3a: Difference between revisions – Wikipedia

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| Symbol = Hm3a

| Symbol = Hm3a

| UniProt = C0HKD0

| UniProt = C0HKD0

| Organism= Heteroscodra maculata}}

| = Heteroscodra maculata}

| symbol = π-TRTX-Hm3a

| protein_type = Peptide toxin}

”’π-Theraphotoxin-Hm3a”’ (also called ”’π-TRTX-Hm3a”’, or ”’H3ma”’) is a 37-amino-[[peptide]] toxin derived from the venom of Togo starburst tarantula [[Heteroscodra maculata]]. Hm3a is a close structural analogue of well-researched [[Psalmotoxin]] (PcTx1) and represents one of the few spider-derived ligands known to target ASICs ([[acid-sensing ion channel]]s).

”’π-Theraphotoxin-Hm3a”’ (also called ”’π-TRTX-Hm3a”’, or ”’H3ma”’) is a 37-amino-[[peptide]] toxin derived from the venom of Togo starburst tarantula [[Heteroscodra maculata]]. Hm3a is a close structural analogue of well-researched [[Psalmotoxin]] (PcTx1) and represents one of the few spider-derived ligands known to target ASICs ([[acid-sensing ion channel]]s).

<ref> Er, S.Y. , Cristofori-Armstrong, B., Escoubas, P., Rash, L.D., (2017) Discovery and molecular interaction studies of a highly stable, tarantula peptide modulator of acid-sensing ion channel 1, Neuropharmacology, Volume 127, Pages 185-195, ISSN 0028-3908, https://doi.org/10.1016/j.neuropharm.2017.03.020.</ref>

<ref> Er, S.Y. , Cristofori-Armstrong, B., Escoubas, P., Rash, L.D., (2017) Discovery and molecular interaction studies of a highly stable, tarantula peptide modulator of acid-sensing ion channel 1, Neuropharmacology, Volume 127, Pages 185-195, ISSN 0028-3908, https://doi.org/10.1016/j.neuropharm.2017.03.020.</ref>

==Etymology and Source==

==Etymology and ==

The name π -Theraphotoxin-Hm3a follows the nomenclature for animal toxins proposed by King et al. <ref>King GF, Gentz MC, Escoubas P, Nicholson GM. A rational nomenclature for naming peptide toxins from spiders and other venomous animals. Toxicon. 2008 Aug 1;52(2):264-76. https://doi.org/10.1016/j.toxicon.2008.05.020 Epub 2008 Jun 13. PMID: 18619481.</ref>: π designates that the toxin acts on proton-gated channels (ASICs), therapotoxin refers to its origin from a [[theraphosid]] (the African Heteroscodra maculata tarantula or “baboon spider”), and Hm3a indicates the species name Heteroscodra maculata, as well as the fact that it is the third peptide purified from its venom.

The name π -Theraphotoxin-Hm3a follows the nomenclature for animal toxins proposed by King et al. <ref>King GF, Gentz MC, Escoubas P, Nicholson GM. A rational nomenclature for naming peptide toxins from spiders and other venomous animals. Toxicon. 2008 Aug 1;52(2):264-76. https://doi.org/10.1016/j.toxicon.2008.05.020 Epub 2008 Jun 13. PMID: 18619481.</ref>: π designates that the toxin acts on proton-gated channels (ASICs), therapotoxin refers to its origin from a [[theraphosid]] (the African Heteroscodra maculata tarantula or “baboon spider”), and Hm3a indicates the species name Heteroscodra maculata, as well as the fact that it is the third peptide purified from its venom.

==Chemistry and Stability==

==Chemistry and ==

Hm3a is a 37-amino acid peptide stabilized by three [[disulfide bonds]] that likely fold it into an [[inhibitor cystine knot]] (ICK) structure, a common motif among [[spider toxins]] that gives it a strong resistance to heat and enzymatic breakdown. It belongs to the Theraphotoxin family, and shares ~82% sequence identity with Psalmotoxin-1 (PcTx1) but lacks the three [[C-terminal]] residues of PcTx1 and contains five amino-acid substitutions. This chemical structural difference might be a reason why Hm3a is more stable than its closest relative PcTx1 in experimental settings; with ~87% intact Hm3a peptide after 48h in human serum, compared to ~35% intact PcTx1 and ~40% oxytocin (clinical control). It also appears to have greater thermal stability, with ~10% loss after 48h in phosphate-buffered saline at ~55°C compared to a ~24% loss for PcTx1 and ~38% loss for oxytocin.<ref name=”Er2017″>Er, S.Y., Cristofori-Armstrong, B., Escoubas, P., Rash, L.D., (2017) Discovery and molecular interaction studies of a highly stable, tarantula peptide modulator of acid-sensing ion channel 1, Neuropharmacology, Volume 127, Pages 185-195, ISSN 0028-3908, https://doi.org/10.1016/j.neuropharm.2017.03.020. </ref>

Hm3a is a 37-amino acid peptide stabilized by three [[disulfide bonds]] that likely fold it into an [[inhibitor cystine knot]] (ICK) structure, a common motif among [[spider toxins]] that gives it a strong resistance to heat and enzymatic breakdown. It belongs to the Theraphotoxin family, and shares ~82% sequence identity with Psalmotoxin-1 (PcTx1) but lacks the three [[C-terminal]] residues of PcTx1 and contains five amino-acid substitutions. This chemical structural difference might be a reason why Hm3a is more stable than its closest relative PcTx1 in experimental settings; with ~87% intact Hm3a peptide after 48h in human serum, compared to ~35% intact PcTx1 and ~40% oxytocin (clinical control). It also appears to have greater thermal stability, with ~10% loss after 48h in phosphate-buffered saline at ~55°C compared to a ~24% loss for PcTx1 and ~38% loss for oxytocin.<ref name=”Er2017″>Er, S.Y., Cristofori-Armstrong, B., Escoubas, P., Rash, L.D., (2017) Discovery and molecular interaction studies of a highly stable, tarantula peptide modulator of acid-sensing ion channel 1, Neuropharmacology, Volume 127, Pages 185-195, ISSN 0028-3908, https://doi.org/10.1016/j.neuropharm.2017.03.020. </ref>

Its theoretical monoisotopic mass (oxidized form) is 4285 Da. it’s sequence is EPCIPKWKSCVNRHGDCCAGLECWKRRKSFEVCVPKV<ref>https://www.uniprot.org/uniprotkb/C0HKD0/entry#sequences</ref>

Its theoretical monoisotopic mass (oxidized form) is 4285 Da.

sequence is EPCIPKWKSCVNRHGDCCAGLECWKRRKSFEVCVPKV<ref>..</ref>

==Target==

==Target==

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At concentrations up to 10µM, Hm3a shows no effect on several rat [[voltage-gated ion channels]], including NaV1.2 ([[SCN2A]]), KV10.1 ([[KCNH1]]), and KV11.1 ([[KCNH2]]), indicating high selectivity for ASICs <ref name=”Er2017″></ref>.

At concentrations up to 10µM, Hm3a shows no effect on several rat [[voltage-gated ion channels]], including NaV1.2 ([[SCN2A]]), KV10.1 ([[KCNH1]]), and KV11.1 ([[KCNH2]]), indicating high selectivity for ASICs <ref name=”Er2017″></ref>.

==Mode of action and Toxicity==

==Mode of action and ==

The mode of action of Hm3a is analogous to that of PcTx1, which has been well characterized. Hm3a mimics the interaction of protons with ASIC1a by binding into ASIC1a’s acidic pocket, which stabilizes the channel in a non-conducting state known as steady-state desensitization (SSD), in which ion flow ceases despite continued exposure to acidic conditions. Under normal circumstances, SSD occurs during sustained mild [[acidosis]] and reverses as the extracellular pH returns to neutral. Hm3a shifts the pH of SSD towards more alkaline values (by 0.37 pH units), promoting desensitization of ASICs even at near-neutral pH and inhibiting sodium flux into the cell.

The mode of action of Hm3a is analogous to that of PcTx1, which has been well characterized. Hm3a mimics the interaction of protons with ASIC1a by binding into ASIC1a’s acidic pocket, which stabilizes the channel in a non-conducting state known as steady-state desensitization (SSD), in which ion flow ceases despite continued exposure to acidic conditions. Under normal circumstances, SSD occurs during sustained mild [[acidosis]] and reverses as the extracellular pH returns to neutral. Hm3a shifts the pH of SSD towards more alkaline values (by 0.37 pH units), promoting desensitization of ASICs even at near-neutral pH and inhibiting sodium flux into the cell.

In contrast, binding of Hm3a to ASIC1b slows channel desensitization and stabilizes the open state, resulting in potentiation.<ref name=”Er2017″></ref>

In contrast, binding of Hm3a to ASIC1b slows channel desensitization and stabilizes the open state, resulting in potentiation.<ref name=”Er2017″></ref>

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While Hm3a has not been tested clinically, its potency, ASIC1 subtype selectivity, and high biological stability make it valuable as a research tool for this purpose <ref name=”Er2017″></ref>. Furthermore, the related molecule PcTx1, with a similar mechanism of action, was tested in animal trials for the treatment of pain, ischemia-associated neuronal death, seizure management and depression, with positive preliminary results <ref>Baron A & Lingueglia E (2015). “Pharmacology of acid-sensing ion channels—Physiological and therapeutic perspectives.” Neuropharmacology 94: 19–35. https://doi.org/10.1016/j.neuropharm.2015.01.005</ref>.

While Hm3a has not been tested clinically, its potency, ASIC1 subtype selectivity, and high biological stability make it valuable as a research tool for this purpose <ref name=”Er2017″></ref>. Furthermore, the related molecule PcTx1, with a similar mechanism of action, was tested in animal trials for the treatment of pain, ischemia-associated neuronal death, seizure management and depression, with positive preliminary results <ref>Baron A & Lingueglia E (2015). “Pharmacology of acid-sensing ion channels—Physiological and therapeutic perspectives.” Neuropharmacology 94: 19–35. https://doi.org/10.1016/j.neuropharm.2015.01.005</ref>.

==External Links==

==External ==

* https://www.ncbi.nlm.nih.gov/protein/C0HKD0.1?report=genpept (Protein profile and sequence)

* https://www.ncbi.nlm.nih.gov/protein/C0HKD0.1 Protein profile and sequence

* https://www.uniprot.org/uniprotkb/C0HKD0/entry (Protein profile and sequence)

* https://www.uniprot.org/uniprotkb/C0HKD0/entry Protein profile and sequence

== References ==

== References ==

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{{reflist}}

{{reflist}}

[[:Category:Spider toxins]]

[[Category:Spider toxins]]

[[:Category:Neurotoxins]]

[[Category:Neurotoxins]]

[[:Category:Ion channel toxins]]

[[Category:Ion channel toxins]]

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{{Infobox nonhuman protein
| image = Π-Theraphotoxin-Hm3a.png
| caption = Predicted structure of the Hm3a peptide generated by AlphaFold. Colors correspond to the pLDDT, i.e., the model’s confidence in the structure
| Symbol = Hm3a
| UniProt = C0HKD0
| organism= Heteroscodra maculata}
| symbol = π-TRTX-Hm3a
| protein_type = Peptide toxin}

π-Theraphotoxin-Hm3a (also called π-TRTX-Hm3a, or H3ma) is a 37-amino-peptide toxin derived from the venom of Togo starburst tarantula Heteroscodra maculata. Hm3a is a close structural analogue of well-researched Psalmotoxin (PcTx1) and represents one of the few spider-derived ligands known to target ASICs (acid-sensing ion channels).
^[1]

Etymology and source

The name π -Theraphotoxin-Hm3a follows the nomenclature for animal toxins proposed by King et al. ^[2]: π designates that the toxin acts on proton-gated channels (ASICs), therapotoxin refers to its origin from a theraphosid (the African Heteroscodra maculata tarantula or “baboon spider”), and Hm3a indicates the species name Heteroscodra maculata, as well as the fact that it is the third peptide purified from its venom.

Chemistry and stability

Hm3a is a 37-amino acid peptide stabilized by three disulfide bonds that likely fold it into an inhibitor cystine knot (ICK) structure, a common motif among spider toxins that gives it a strong resistance to heat and enzymatic breakdown. It belongs to the Theraphotoxin family, and shares ~82% sequence identity with Psalmotoxin-1 (PcTx1) but lacks the three C-terminal residues of PcTx1 and contains five amino-acid substitutions. This chemical structural difference might be a reason why Hm3a is more stable than its closest relative PcTx1 in experimental settings; with ~87% intact Hm3a peptide after 48h in human serum, compared to ~35% intact PcTx1 and ~40% oxytocin (clinical control). It also appears to have greater thermal stability, with ~10% loss after 48h in phosphate-buffered saline at ~55°C compared to a ~24% loss for PcTx1 and ~38% loss for oxytocin.^[3]

Its theoretical monoisotopic mass (oxidized form) is 4285 Da.
Its sequence is: EPCIPKWKSCVNRHGDCCAGLECWKRRKSFEVCVPKV.^[4]

Target

Hm3a primarily acts on ASICs (members of the DEG/ENaC family), which are ion channels that detect decreases in extracellular pH, and allow sodium to flow inside the cell as a response to protonation. There are six ASIC isoforms (ASIC1a, ASIC1b, ASIC2a, ASIC2b, ASIC3 and ASIC4), but Hm3a is only highly selective to ASIC1 subunits, strongly inhibiting ASIC1a and potentiating ASC1b, with negligeable activity on ASIC2a or ASIC3 at concentrations up to 10µM ^[3].

Main effect of Hm3a (recombinant) on ASIC receptors for rat and human variants^[3]

Channel Subtype	Effect	Potency
rASIC1a	Inhibition	IC₅₀ = 1.3 ± 0.2 nM
rASIC1b	Potentiation	EC₅₀ = 46.5 ± 6.2 nM
rASIC1a/1b (heteromeric)	Potentiation	EC₅₀ = 17.4 ± 0.5 nM
hASIC1a	Inhibition	IC₅₀ = 39.7 ± 1.1 nM
hASIC1b	Potentiation	EC₅₀ = 178.1 ± 1.3 nM

As the recombinant Hm3a has a smaller potency compared to PcTx1, a mutant version was designed (Hm3a_P38) with the addition of a proline at the C-terminus. Such recombinant yields a 3.3-fold increase in potency on ASIC1a compared to the Hm3a wild type. This increased potency indicates the possibility of using Hm3a as a template for designing effective therapeutic tools.

Comparison of the potency of Hm3a recombinant and Hm3a mutant on ASIC1a^[3]

Variant	Effect	Potency
Hm3a_WT (wild type)	Inhibition	IC₅₀ = 1.3 ± 0.2 nM
Hm3a_P38 (mutant)	Inhibition	IC₅₀ = 0.4 ± 0.1 nM

At concentrations up to 10µM, Hm3a shows no effect on several rat voltage-gated ion channels, including NaV1.2 (SCN2A), KV10.1 (KCNH1), and KV11.1 (KCNH2), indicating high selectivity for ASICs ^[3].

Mode of action and toxicity

The mode of action of Hm3a is analogous to that of PcTx1, which has been well characterized. Hm3a mimics the interaction of protons with ASIC1a by binding into ASIC1a’s acidic pocket, which stabilizes the channel in a non-conducting state known as steady-state desensitization (SSD), in which ion flow ceases despite continued exposure to acidic conditions. Under normal circumstances, SSD occurs during sustained mild acidosis and reverses as the extracellular pH returns to neutral. Hm3a shifts the pH of SSD towards more alkaline values (by 0.37 pH units), promoting desensitization of ASICs even at near-neutral pH and inhibiting sodium flux into the cell.
In contrast, binding of Hm3a to ASIC1b slows channel desensitization and stabilizes the open state, resulting in potentiation.^[3]

No toxicity has been reported.

Therapeutic use

ASICs normally contribute to the detection of tissue acidosis in mammals by triggering appropriate pain and protective responses. However, excessive or prolonged activation can lead to neuronal injury and cell death.^[5][6]

As some spiders secrete a wide range of toxins in their venom, including ASIC-modulating toxins, their isolation and analysis proves valuable for designing therapeutic tools aimed at mitigating dysfunctional ASIC activity through selective inhibition or potentiation.

While Hm3a has not been tested clinically, its potency, ASIC1 subtype selectivity, and high biological stability make it valuable as a research tool for this purpose ^[3]. Furthermore, the related molecule PcTx1, with a similar mechanism of action, was tested in animal trials for the treatment of pain, ischemia-associated neuronal death, seizure management and depression, with positive preliminary results ^[7].

External links

References