Cloning and functional characterization of a peroxiredoxin 4 from yellowtail kingfish ( Seriola lalandi)

Peroxiredoxins (Prxs) are antioxidant enzymes with a conserved Cys residue at the active site which undergoes peroxide-dependent oxidation followed by thiol-dependent reduction during each catalytic cycle. In mammals, Prx 4 proteins have an N-terminal signal peptide which targets them for secretion from the cell. This has not been investigated in fish. Thus, here we describe the cloning of a Prx 4 cDNA from yellowtail kingfish (YTK, Seriola lalandi) and the elucidation of the signal peptide cleavage site. The YTK Prx 4 cDNA included a 792 bp open reading frame (ORF) encoding a predicted protein of 264 amino acids (referred to as Prx264). SignalP software and a multiple sequence alignment predicted signal peptide cleavage sites after residues 33 and 67 giving rise to Prx231 and Prx197, respectively. All three proteins were expressed in E. coli and assayed for thioredoxin-dependent peroxidase activity. Prx231 and Prx197 both exhibited activity whereas Prx264 did not. Thus, either potential cleavage site may be physiologically relevant. Both active forms of the enzyme displayed a single-displacement reaction mechanism and typical saturable Michaelis–Menten type kinetics. This is unusual for Prx enzymes. In addition, they both displayed a clear preference for H 2O 2 over cumene hydroperoxide or t-butyl hydroperoxide.