Molecular biology has revealed that Grammostola mechanotoxin #4, or GsMTx4, is an inhibitory cysteine knot peptide (ICK) that inhibits mechanosensitive ion channels (MSCs). GsMTx4 is a 34-residue peptide, isolated from a tarantula spider. The peptide has hydrophobic and hydrophilic regions. It is capable of penetrating membrane bilayers and partitioning into the water-air interface.
GsMTx4 inhibits cation selective channels, including Piezo1 channels. Interestingly, GsMTx4 inhibits Piezo1 without altering whole-cell voltage-sensitive currents. This is because GsMTx4 does not block the channel pore, but rather, impedes force transfer to the channel. GsMTx4 blocks Piezo1 currents and uptake of Ca 2+ by acinar cells. This activity may contribute to the inhibition of axon and myelin damage.
We found that GsMTx4 remained stably in the shallow mode of binding, despite the presence of brominated lipids. Binding energies were 18-27 kJ/mol. These binding energies were comparable to those measured with Trp.
Inhibition of Piezo1 channels is likely due to a tension-dependent depth change, which is responsible for modulating the area of the outer monolayer. The increased area of the outer leaflet could transfer tension to the inner monolayer. This could result in TREK potentiation.
GsMTx4 also inhibits the activity of Piezo channels in HEK293 cells. In Piezo1 aci KO mice, expression of EYFP was detected in acinar cells. Moreover, in HEK293 cells, Yoda1, a Piezo1 agonist, increased intracellular calcium. However, the increase in surface pressure was not inhibited by Yoda1. This suggests that Yoda1 might be inhibiting the activity of Piezo1 by affecting its surface tension.