Succinate dehydrogenase (SDH) is a mitochondrial
enzyme with the unique ability to participate in both the tricarboxylic acid cycle and the electron transport chain to produce
reactive oxygen species (ROS). The B subunit of SDH is required for
succinate oxidation, which is critical for pro-inflammatory response. In this study, we cloned the
iron-sulfur protein subunit of SDH from Apostichopus japonicus (denoted as AjSDHB) via RACE technology and explored its role in the immune system as a response to pathogen
infection. The full-length
cDNA of AjSDHB was 1442 bp with a complete open reading frame of 858 bp encoding 286
amino acids. Simple modular architecture research tool analysis revealed that AjSDHB contained two conserved domains, including a 2Fe-2S
iron-
sulfur cluster binding domain and a 4Fe-4S dicluster domain, without a
signal peptide. Multiple sequence alignment demonstrated that AjSDHB shared a high degree of structural conservation and sequence identities with other counterparts from invertebrates and vertebrates. Phylogenetic analysis supported the finding that AjSDHB is a new member of the SDHB
protein subfamily. Tissue distribution analysis revealed that AjSDHB was expressed in all examined tissues and particularly highly expressed in the muscles. AjSDHB transcripts were markedly induced in coelomocytes both by Vibrio splendidus challenge in vivo and
lipopolysaccharide exposure in vitro. Function analysis showed that
siRNA-mediated AjSDHB knockdown could substantially reduce the mitochondrial membrane potential (ΔΨm) and further decrease mitochondrial ROS production in A. japonicus coelomocytes. By contrast, AjSDHB overexpression considerably increased ΔΨm and mitochondrial ROS production of A. japonicus coelomocytes. These results supported the idea that AjSDHB is involved in the innate immunity of A. japonicus through its participation in mitochondrial ROS generation.