Abstract:
Catalases are well known antioxidant enzymes that can mainly dismutate hydrogen peroxide into water
and oxygen in order to prevent oxidative stress. The complete genomic DNA (gDNA) sequence of the
catalase gene from rock bream (Oplegnathus fasciatus) was identified from our custom-constructed BAC
genomic DNA library and designated as RbCat. RbCat consists of 13 exons, separated by 12 introns, within
a 13,722-bp gDNA sequence. The complete cDNA sequence (3303 bp) of RbCat is comprised of a 1581-bp
coding region, encoding a peptide of 527 amino acids (aa) in length, with a predicted molecular mass of
60 kDa and a theoretical isoelectric point of 8.34. The anticipated promoter region of RbCat contains
several transcription factor-binding sites, including sites that bind with immune- and antioxidantresponsive signaling molecules, suggesting its substantial transcriptional regulation. RbCat resembles
the typical catalase family signature, i.e., it is composed of the catalase proximal active site motif along
with a catalase proximal heme-ligand signature motif and shares great homology with its fish counterparts. According to multiple sequence alignment, functionally important amino acids present in RbCat
were thoroughly conserved among its vertebrate counterparts. Phylogenetic analysis revealed that RbCat
evolved from a vertebrate origin, and further positioned it in the fish clade. Recombinant RbCat had
noticeable peroxidase activity against its substrate, hydrogen peroxide, in a dose-dependent manner.
However, it demonstrated substantial peroxidase activity within a broad range of temperatures and pH
values. Constitutive RbCat mRNA expression of different magnitudes was detected in a tissue-specific
manner, suggesting its diverse role in physiology with respect to the tissue type. Moreover, immune
challenge experiments using Edwardsiella tarda and rock bream iridovirus (RBIV) as live pathogens and
polyinosinic:polycytidylic acid and lipopolysaccharide as mitogens revealed that the transcription of
RbCat can be modulated by immune stimulation. Collectively, the results obtained in this study suggest
that RbCat can function as a potent antioxidant enzyme in rock bream and may play a role in postimmune responses with respect to its peroxidase activity.
