Vejocalcin  Vejocalcin (VjCa, also called Vejocalcine) is a toxin from the venom of the Mexican scorpion "Vaejovis mexicanus". Vejocalcin is a member of the calcin family of toxins. It acts as a cell-penetrating peptide (CPP); it binds with high affinity and specificity to skeletal ryanodine receptor 1 (RYR1) of the sarcoplasmic reticulum, thereby triggering calcium release from intracellular Ca2+ stores. Vejocalcin is produced by "Vaejovis mexicanus", a scorpion endemic to North and Central America. While "Vaejovis mexicanus" was originally described in 1836, vejocalcin was only isolated in 2016. This toxin was named after the scorpion that produces the peptide as well as its structural similarity to other toxins of the scorpion calcin family. On the basis of its amino acid structure, vejocalcin belongs to the family of scorpion calcin toxins, a group of selective, high-affinity membrane-permeable ligands of RyRs. Vejocalcin shares significant sequence similarity with other members of this family. Vejocalcin has a molecular mass of approximately 3.8 kDa and an isoelectric point of 9.3. It is a relatively small protein, consisting of only 33 amino acids:   Notably, two calcins produced by two closely related scorpions - vejocalcin from "Vaejovis mexicanus" and intrepicalcin from "Vaejovis intrepidus" - display a 97% similarity in their primary sequence, differing in only one amino acid at position 14 (Asn and Lys, respectively). Despite this marked similarlity, vejocalcin exhibits a binding affinity to RyR1 that is 4.7-fold higher than that of intrepicalcin. Vejocalcin shows an arrangement of charged residues, in which most of the positively charged residues are segregated on one side of the molecule, whereas neutral and negatively charged residues are clustered on the opposite side. This arrangement generates a discrete dipole moment (DM) and appears to be a prevalent feature across all toxins of the calcin family. Interestingly, vejocalcin has the smallest charge segregation among peptides in the calcin family. However, comparisons among different calcins show that, for each peptide, there appears to be no correlation between DM, binding affinity and subconductance state attributes.