Identification and Characterization of a Peptide from the Stony Coral Heliofungia actiniformis

Abstract

Marine organisms produce a diverse range of toxins and bioactive peptides to support predation, competition, and defense. The peptide repertoires of stony corals (order Scleractinia) remain relatively understudied despite the presence of tentacles used for predation and defense that are likely to contain a range of bioactive compounds. Here, we show that a tentacle extract from the mushroom coral, Heliofungia actiniformis, contains numerous peptides with a range of molecular weights analogous to venom profiles from species such as cone snails. Using NMR spectroscopy and mass spectrometry we characterized a 12-residue peptide (Hact-1) with a new sequence (GCHYTPFGLICF) and well-defined β-hairpin structure stabilized by a single disulfide bond. The sequence is encoded within the genome of the coral and expressed in the polyp body tissue. The structure present is common among toxins and venom peptides, but Hact-1 does not show activity against select examples of Gram-positive and Gram-negative bacteria or a range of ion channels, common properties of such peptides. Instead, it appears to have a limited effect on human peripheral blood mononuclear cells, but the ecological function of the peptide remains unknown. The discovery of this peptide from H. actiniformis is likely to be the first of many from this and related species.

Marine natural products

“…611 A 12-residue peptide, Hact-1, was isolated from tentacles of the mushroom coral Heliofungia actiniformis . 612 The peptide has one disulfide bond and adopts a well-defined β-hairpin structure – it was inactive against a range of bacteria and ion channels. A daily 28 day exposure of mice to palytoxin induced changes to blood chemistry and established a chronic oral toxicity of LD 50 0.44 μg kg −1 and a no-observed-adverse-effect-level of 0.03 μg kg −1 , suggesting regulatory levels of the toxin should be re-evaluated.…”

Newly Discovered Peptides from the Coral Heliofungia actiniformis Show Structural and Functional Diversity

“…The four new peptides described in this study add to our original discovery of Hact-1, which is a 12-residue β-hairpin peptide from H. actiniformis (Figure 2A). 13 Hact-1 causes a dose−response suppression of TNFα release from human peripheral blood mononuclear cells, and we show here that Hact-2 has significant cell proliferation activity, suggesting a diverse array of bioactivities might ultimately be found for coral peptides. The presence of the β-defensin fold in both Hact-4 and Hact-SCRiP1, despite the extra disulfide bond in the latter, suggests these two peptides have an evolutionary link, and the SCRiPs may have evolved an extra disulfide bond for added stability.…”

“…NMR Spectroscopy. NMR spectra were acquired on the synthetic or native peptides in aqueous solution at approximately 0.5 mM and included two-dimensional TOCSY, NOESY, COSY, and 13 C and 15 N HSQC spectra. Assignment of the resonances was carried out using standard protocols.…”

“…Hact-4 contains eight proline residues, and it was possible to assign the majority of the resonances. It was determined that Pro19 and Pro23 are in the cis-conformation based on NOEs between Hα i /Hδ i+1 and the 13 Cβ and 13 Cγ proline chemical shifts, and this was taken into account during structure calculations. Similar to Hact-2, preliminary structures calculated without disulfide bond restraints were poorly defined and prevented identification of the disulfide connectivity.…”

“…The first peptide identified was Hact-1, a 1.3 kDa peptide that has a modest immunomodulatory effect and contains a well-defined β-hairpin structure stabilized by a single disulfide bond. 13 In the current study we describe four new peptides from H. actiniformis, and our study highlights stony corals as a source of unique peptides with diverse three-dimensional structures. We suggest that the structures of these peptides may provide insights into their role and help classify them into well-described families.…”