Fungi fibrinolytic compound 1 (FGFC1) is a rare marine-derived compound that can enhance fibrinolysis both in vitro and in vivo. The fibrinolytic activity characterization of FGFC1 mediated by plasminogen (Glu-/Lys-) and a single-chain urokinase-type plasminogen activator (pro-uPA) was further evaluated. The binding sites and mode of binding between FGFC1 and plasminogen were investigated by means of a combination of in vitro experiments and molecular docking. A 2.2-fold enhancement of fibrinolytic activity was achieved at 0.096 mM FGFC1, whereas the inhibition of fibrinolytic activity occurred when the FGFC1 concentration was above 0.24 mM. The inhibition of fibrinolytic activity of FGFC1 by 6-aminohexanoic acid (EACA) and tranexamic acid (TXA) together with the docking results revealed that the lysine-binding sites (LBSs) play a crucial role in the process of FGFC1 binding to plasminogen. The action mechanism of FGFC1 binding to plasminogen was inferred, and FGFC1 was able to induce plasminogen to exhibit an open conformation by binding through the LBSs. The molecular docking results showed that docking of ligands (EACA, FGFC1) with receptors (KR1–KR5) mainly occurred through hydrophilic and hydrophobic interactions. In addition, the binding affinity values of EACA to KR1–KR5 were −5.2, −4.3, −3.7, −4.5, and −4.3 kcal/moL, respectively, and those of FGFC1 to KR1–KR5 were −7.4, −9.0, −6.3, −8.3, and −6.7 kcal/moL, respectively. The findings demonstrate that both EACA and FGFC1 bound to KR1–KR5 with moderately high affinity. This study could provide a theoretical basis for the clinical pharmacology of FGFC1 and establish a foundation for practical applications of FGFC1.

One of the supporting factors behind the biomolecules recently used in anti-aging and skin nourishment is their antioxidant properties. Hydrogen peroxide (H₂O₂) is a well-known small molecule oxidant that induces apoptosis in human skin fibroblast (HSF) cells through the synthesis of inflammatory cytokines. Hence, this study aimed to investigate the antioxidant activities of protein hydrolysates prepared from Iris squid (Symplectoteuthis oualaniensis) (PHCSO) in vitro. Firstly, two peptides with MWs more than 10 kDa (PHCSO-1) and less than 10 kDa (PHCSO-2) were obtained through ultrafiltration and were characterized (molecular pattern amino acid composition, FTIR) before testing the antioxidant activity (DPPH radical scavenging activity and hydroxyl radical scavenging activity). Then, the effects of PHCSOs on HSF cell viability, H₂O₂-induced oxidative stress model of HSF cells, ROS fluorescence staining, level of cytokines (IL-1, IL-6 and TNF-α) and cellular antioxidant properties (SOD activity, CAT activity, GSH and MDA content) were investigated. The cell morphology was examined through fluorescence staining and inflammatory factors and antioxidant activity analysis showed that superior properties were observed in PHCSO-2 peptide compared to PHCSO-1 and PHCSO. Among the peptides, PHCSO-2 (5 mg/mL) had higher DPPH and hydroxyl radical scavenging activities of 58% and 57%, respectively. On the other hand, the PHCSO-2 treatment reduced the TNF-α activity by 25%, which indicated the effective protection of PHCSO-2 from oxidative stress damage in the skin. These findings proved that peptides with less than 10 kDa were more suitable for therapeutic purposes, with good antioxidant properties. Accordingly, the protein hydrolysate from S. oualaniensis proved to be an excellent marine-based antioxidant peptide, which could be applied in cosmetic, pharmaceutical and food industries.