Asteropsin A: An unusual cystine-crosslinked peptide from porifera enhances neuronal Ca^{2 +} influx

Background Herein we report the discovery of a cystine-crosslinked peptide from Porifera along with high-quality spatial details accompanied by the description of its unique effect on neuronal calcium influx. Methods Asteropsin A (ASPA) was isolated from the marine sponge Asteropus sp., and its structure was independently determined using X-ray crystallography (0.87 Å) and solution NMR spectroscopy. Results An N-terminal pyroglutamate modification, uncommon cis proline conformations, and absence of basic residues helped distinguish ASPA from other cystine-crosslinked knot peptides. ASPA enhanced Ca^{2 +} influx in murine cerebrocortical neuron cells following the addition of the Na⁺ channel activator veratridine but did not modify the oscillation frequency or amplitude of neuronal Ca^{2 +} currents alone. Allosterism at neurotoxin site 2 was not observed, suggesting an alternative to the known Na⁺ channel interaction. Conclusions Together with a distinct biological activity, the origin of ASPA suggests a new subclass of cystine-rich knot peptides associated with Porifera. General significance The discovery of ASPA represents a distinctive addition to an emerging subclass of cystine-crosslinked knot peptides from Porifera.