Elevated cadmium (Cd) concentrations in fishery byproducts are an environmental concern, that might
be reduced by enzymatic removal and adsorption of the contaminants during recycling the byproducts as animal
food. We cloned the gene for Arthrobacter nicotinovorans serine protease (ANISEP), which was isolated from
the hepatopancreas of the Japanese scallop (Patiopecten yessoensis) and has been found to be an effective enzyme
for Cd(II) removal. The gene is 993 bp in length and encodes 330 amino acids, including the pre (1–30)
and pro (31–111) sequences. The catalytic triad consists of His, Asp, and Ser. Sequence similarities indicate that
ANISEP is a extracellular serine protease. X-ray crystallography revealed structural similarities between ANISEP and the
trypsin-like serine protease NAALP from Nesterenkonia sp. Site-directed mutagenesis identified Ser171 as catalytic residue.
The keratinolytic activity of ANISEP was 10-fold greater than that of trypsin. ANISEP digested Cd(II)-bound recombinant
metallothionein MT-10a from Laternula elliptica, but did not release Cd. These results further suggest
ANISEP is a trypsin-like serine protease that can release Cd from the Japanese scallop hepatopancreas because of its
strong keratinolytic activity.
Keywords: Arthrobacter nicotinovorans, cadmium, crystallization, metallothionein, scallops, serine protease.
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