Recombinant expression of Intrepicalcin from the scorpion Vaejovis intrepidus and its effect on skeletal ryanodine receptors.

Background: Scorpion venoms contain toxins that modulate ionic channels, among which are the calcins, a small group of short, basic peptides with an Inhibitor Cystine Knot (ICK) motif that target calcium release channels/ryanodine receptors (RyRs) with high affinity and selectivity. Here we describe the heterologous expression of Intrepicalcin, identified by transcriptomic analysis of venomous glands from Vaejovis intrepidus.

Methods: Recombinant Intrepicalcin was obtained in Escherichia coli BL21-DE3 (periplasm) by fusing the Intrepicalcin gene to sequences coding for signal-peptide, thioredoxin, His-tag and enterokinase cleavage site.

Results: [H]Ryanodine binding, used as a functional index of RyR activity, revealed that recombinant Intrepicalcin activates skeletal RyR (RyR1) dose-dependently with K=17.4±4.0nM. Intrepicalcin significantly augments the bell-shaped [Ca]-[H]ryanodine binding curve at all [Ca] ranges, as is characteristic of the calcins. In single channel recordings, Intrepicalcin induces the appearance of a subconductance state in RyR1 with a fractional value ∼55% of the full conductance state, very close to that of Vejocalcin. Furthermore, Intrepicalcin stimulates Ca release at an initial dose=45.3±2.5nM, and depletes ~50% of Ca load from skeletal sarcoplasmic reticulum vesicles.

Conclusions: We conclude that active recombinant Intrepicalcin was successfully obtained without the need of manual oxidation, enabling it to target RyR1s with high affinity.

General Significance: This is the first calcin heterologously expressed in the periplasma of Escherichia coli BL21-DE3, shown to be pharmacologically effective, thus paving the way for the generation of Intrepicalcin variants that are required for structure-function relationship studies of calcins and RyRs.