Antimicrobial peptides (AMPs) may be the most promising substitute for antibiotics due to their effective antimicrobial activities and multiple function mechanisms against pathogenic microorganisms. In this study, a novel AMP containing 51 amino acids, named Lc1687, was screened from the large yellow croaker (Larimichthys crocea) via a B. subtilis system. Bioinformatics and circular dichroism (CD) analyses showed that Lc1687 is a novel anionic amphiphilic α-helical peptide, which was derived from the C-terminal of a Ferritin heavy subunit. The recombinant Lc1687 (named rLc1687) purified from Escherichia coli exhibited strong activities against Gram-positive (Gram+) bacterium Staphylococcus aureus, Gram-negative (Gram-) bacteria Vibrio vulnificus, V. parahaemolyticus, and Scuticociliatida. Scanning electron microscope (SEM) and transmission electron microscopy (TEM) revealed the possible function mechanisms of this peptide, which is to target and disrupt the bacterial cell membranes, including pore-forming, loss of fimbriae, and cytoplasm overflow, whereas gel retardation assay revealed that peptide Lc1687 cannot bind bacterial DNA. The peptide stability analysis showed that rLc1687 acts as a stable antimicrobial agent against Gram+ and Gram- bacteria at temperatures ranging from 25 to 100°C, pH 3-12, and UV radiation time ranging from 15 to 60 min. A hemolytic activity assay confirmed that this peptide may serve as a potential source for clinical medicine development. Taken together, Lc1687 is a novel AMP as it is a firstly confirmed Ferritin fragment with antimicrobial activity. It is also a promising agent for the development of peptide-based antibacterial and anti-parasitic therapy.

ASC (apoptosis-associated speck-like protein containing a caspase recruitment domain (CARD)) is the only adaptor involved in the formation of multiple types of inflammasomes. Accumulating evidence demonstrates that ASC plays a critical role in the protection of the host against pathogen infection. In this study, we identified an ASC gene in the large yellow croaker (Larimichthys crocea), namely LcASC, and then investigated the expression characteristics and related signal pathways. On one hand, LcASC has several conserved protein modules, i.e., an N-terminal PYD region, a C-terminal CARD region, and twelve α-helix structures. On the other hand, it has a high variable linker between PYD and CARD domains. Moreover, LcASC has varying degrees of expression in different tissues, among which the highest expression is observed in the spleen followed by the gills and skin. It also shows induced expressions in the head kidney, liver, and spleen following immune stimulation, especially Vibrio Parahaemolyticus infection. Further subcellular localization analysis showed that LcASC formed a clear aggregated speck in the cytoplasm close to the nucleus. In addition, we found 46 DEGs in a comparative transcriptome analysis between the LcASC overexpression group and the control vector group. Notedly, the up-regulated gene Fos and down-regulated gene DOK3 in LcASC overexpressed cells play important roles in the immune system. How ASC contacts these two genes needs to be clarified in upcoming studies. These findings collectively provide new insights into finfish ASC and its potential regulatory signaling pathway as well.