Publication Date:
2015-03-28
Description:
Fish have a complex self-defense mechanism against microbial invasion. Recently, l -lysine α-oxidases have been identified from a number of fish species as a novel type of antibacterial protein in the integument. These enzymes exhibit strict substrate specificity for l -lysine, but the underlying mechanisms and details of their catalytic properties remain unknown. In this study, a synthetic gene coding for Scomber japonicus l -lysine α-oxidase, originally termed AIP (for apoptosis-inducing protein), was expressed in Pichia pastoris , and the recombinant enzyme (rAIP) was purified and characterized. rAIP exhibited essentially the same substrate specificity as the native enzyme, catalyzing the oxidative deamination of l -lysine as an exclusive substrate. rAIP was N -glycosylated and remained active over a wide range of pH, with an optimal pH of 7.5. The enzyme was stable in the pH range from 4.5 to 10.0 and was thermally stable up to 60°C. A molecular modelling of rAIP and a comparative structure/sequence analysis with homologous enzymes indicate that Asp 220 and Asp 320 are the substrate-binding residues that are likely to confer exclusive substrate specificity for l -lysine on the fish enzymes.
Print ISSN:
0021-924X
Electronic ISSN:
1756-2651
Topics:
Biology
,
Chemistry and Pharmacology
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