Asteropsin A: An unusual cystine-crosslinked peptide from porifera enhances neuronal Ca2+ influx

Abstract

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 Ca2+ 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 Ca2+ 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.

Asteropsins B–D, sponge-derived knottins with potential utility as a novel scaffold for oral peptide drugs

“…The MALDI-TOF MS of asteropsins B–D exhibited monoisotopic pseudomolecular ion peaks at m/z 3919.5 [M + Na] + ; 3787.5 [M + Na] + ; and 3426.2 [M + H] + , respectively. Previously isolated pyroglutamyl dipeptides [32] and asteropsin A (ASPA) [20] from the same sponge aided confirmation of the presence of a pyroglutamyl ring NH (δ H 7.82–7.84 ppm) based on signal shape, chemical shift, and HMBC (DMSO- d 6 ) correlations. NMR evidence and difficulties with traditional sequence analysis indicated that the N -terminus of each peptide was blocked by a pyroglutamic acid (pGlu).…”

“…ASPB and ASPC were found to have two highly conserved cis prolines (Pro 27 and Pro 30 in ASPB; and Pro 25 and Pro 28 in ASPC) located at the end of the second and before the third β-strands, respectively; this conformation was also conserved in ASPA [20]. …”

“…During our investigations of the effects of ASPA and ASPC on neuronal Ca 2+ influx, it was found that ASPA significantly enhanced veratridine-induced Ca 2+ influx in murine cerebrocortical neuron cells at an EC 50 value of 14 nM [20]. However, despite a similar sequence pattern and a highly comparable tertiary structure (Fig.…”

“…Relatively few marine-derived knottins have been discovered in sources other than cone snails. In 2006, Fusetani et al first identified asteropine A (APA; a bacterial sialidase inhibitor) in the marine sponge Asteropus simplex [19]; and later, we isolated asteropsin A (ASPA) from the same sponge genus and validated Porifera as a source of unusual knottin-like peptides [20]. The N -terminal modification, absence of basic residues, the cis conformation of prolines of ASPA and its unique bioactivity distinguish it from other reported knottins.…”

Solution Structure of a Sponge-Derived Cystine Knot Peptide and Its Notable Stability

“…In particular, asteropsins A–D exhibit notable stabilities in the gastrointestinal tract and in human plasma. 8,9 Peptides of the knottin family have been reported from a diverse variety of organisms, but few marine-derived knottins have been discovered other than those from the cone snail family. Asteropine A (APA) was first reported in Asteropus simplex (a marine sponge) as a bacterial sialidase inhibitor.…”