A bivalent remipede toxin promotes calcium release via ryanodine receptor activation

Comparison of the structure-function of five newly members of the calcin family

Calcins are a group of scorpion toxin peptides specifically binding to ryanodine receptors (RyRs) with high affinity, and have the ability to activate and stabilize RyR in a long-lasting subconductance state. Five newly calcins synthesized compounds exhibit typical structural characteristics of a specific family through chemical synthesis and virtual analysis. As the calcins from the same species, Petersiicalcin1 and Petersiicalcin2, Jendekicalcin2 and Jendekicalcin3, have only one residue difference. Both Petersiicalcin1 and Petersiicalcin2 exhibited different affinities in stimulating [3H]ryanodine binding, but the residue mutation resulted in a 2.7 folds difference. Other calcins also exhibited a stimulatory effect on [3H]ryanodine binding to RyR1, however, their affinities were significantly lower than that of Petersiiicalcin1 and Petersiiicalcin2. The channel domain of RyR1 was found to be capable of binding with the basic residues of these calcins, which also exhibited interactions with the S6 helices on RyR1. Dynamic simulations were conducted for Petersiicalcin1 and Petersiicalcin2, which demonstrated their ability to form a highly stable conformation and resulting in an asymmetric tetramer structure of RyR1. The discovery of five newly calcins further enriches the diversity of the natural calcin family, which provides more native peptides for the structure-function analysis between calcin and RyRs.

Structural Basis of the Bivalency of the TRPV1 Agonist DkTx

Bivalency is a prevalent natural mechanism to enhance receptor avidity. Various two-domain disulfide-rich peptides exhibiting bivalent action have been identified from animal venoms. A unique characteristic of these peptides is that they induce a pharmacological response different from that provoked by any of the constituent domains. The enhanced potency and avidity of such peptides is therefore a consequence of their domain fusion by a peptide linker. The role of the linker itself, beyond conjugation, remains unclear. Here, we investigate how the linker affects the bivalency of the capsaicin receptor (TRPV1) agonist DkTx. We recombinantly produced isotope labelled DkTx using a protein splicing approach, to solve the high-resolution solution structure of DkTx, revealing residual linker order stabilised by linker-domain interactions leading to biased domain orientations. The significance of this was studied using a combination of mutagenesis, spin relaxation studies and electrophysiology measurements. Our results reveal that disrupting the pre-organisation of the domains of DkTx is accompanied by reductions in potency and onset of avidity. Our findings support a model of pre-configured two-domain binding, in favour of the previously suggested sequential binding model. This highlights the significance of ordered elements in linker design and the natural evolution of these in bivalent toxins.