Neuroprotective Kunitz-like peptides identified from the octopus coral Galaxea fascicularis through transcriptomic analysis

Parkinson's disease (PD) is the second most common neurodegenerative disease. Potassium voltage-gated channels are potential targets for the treatment of PD. The aim of this study is to identify novel potassium ion channel blockers for the treatment of PD through transcriptomic analysis of the coral species Galaxea fascicularis. After annotation by four different databases, four peptides were selected that showed characteristics of potassium ion channel blockers. These four peptides were subjected to multiple sequence alignment and phylogenetic analysis. These four peptides were identified as of Kunitz-type peptides, are known as potassium ion channel blockers. The structures of the peptides were modeled and subjected to molecular dynamics (MD) simulation to verify their stability, which indicated that the peptide GfKuz1 showed the highest potency to block K_V1.3 (potassium voltage-gated channel subfamily A member 3) among the reference peptides. The MD simulation of the peptide-protein complexes showed that GfKuz1 interacted with K_V1.3, and was more compact and stable than the other potassium ion channel. The blocking effect was confirmed by a potassium ion bioassay. Furthermore, GfKuz1 showed no toxicity to PC-12 ​cells or zebrafish at concentrations up to 100 ​μM. In addition, GfKuz1 increased the PC-12 ​cell viability that was reduced by 6-hydroxydopamine hydrochloride, and also down-regulated the level of reactive oxygen species and activated the Nrf2 pathway. In summary, GfKuz1 reversed PD symptoms and is a potential peptide drug prototype for PD treatment.