Identification and tissue-specific expression of a promethin-like homolog in amphioxus Branchiostoma belcheri

Identification and biochemical characterization of polyamine oxidases in amphioxus: Implications for emergence of vertebrate-specific spermine and acetylpolyamine oxidases

Polyamine oxidases (PAOs) have been identified in a wide variety of animals, as well as in fungi and plant. Generally, plant PAOs oxidize spermine (Spm), spermidine (Spd) and their acetylated derivatives, N(1)-acetylspermine (N(1)-Aspm) and N(1)-acetylspermidine (N(1)-Aspd), while yeast PAOs oxidize Spm, N(1)-Aspm and N(1)-Aspd, but not Spd. By contrast, two different enzymes, namely spermine oxidase (SMO) and acetylpolyamine oxidase (APAO), specifically catalyze the oxidation of Spm and N(1)-Aspm/N(1)-Aspd, respectively. However, our knowledge on the biochemical and structural characterization of PAOs remains rather limited, and their evolutionary history is still enigmatic. In this study, two amphioxus (Branchiostoma japonicum) PAO genes, named Bjpao1 and Bjpao2, were cloned and characterized. Both Bjpao1 and Bjpao2 displayed distinct tissue-specific expression patterns. Notably, rBjPAO1 oxidized both spermine and spermidine, but not N(1)-acetylspermine, whereas rBjPAO2 oxidizes both spermidine and N(1)-acetylspermine, but not spermine. To understand structure-function relationship, the enzymatic activities of mutant BjPAOs that were generated by site-directed mutagenesis and expressed in E. coli were examined, The results indicate that the residues H64, K301 and T460 in rBjPAO1, and H69, K315 and T467 in rBjPAO2 were all involved in substrate binding and enzyme catalytic activity to some extent. Based on our results and those of others, a model depicting the divergent evolution and functional specialization of vertebrate SMO and APAO genes is proposed.

A trypsin homolog in amphioxus: expression, enzymatic activity and evolution

Trypsin has been documented in a variety of species including both vertebrates and invertebrates, but little is known about it in amphioxus, a model organism for insights into the origin and evolution of vertebrates. Here we identified a trypsin gene in Branchiostoma japonicum. The cDNA was 978 bp long with an ORF encoding a deduced protein of 272 amino acids. The deduced protein had an N-terminal signal peptide of 15 amino acids, a 16 activation peptide with the typical cleavage site Arg/Ile, a Tryp_SPc domain with the catalytic triad His(72)-Asp(118)-Ser(215) and the S1 substrate binding residue Asp(209), which are all characteristic of trypsinogens. The recombinant trypsin protein was able to hydrolyse the trypsin prototypic substrate BAEE, which was inhibited by the trypsin-specific inhibitor soybean trypsin inhibitor. Both northern blotting and tissue-section in situ hybridization demonstrated that trypsin gene was expressed in a tissue-specific manner, with most abundant levels in the hepatic caecum, mid-gut and ovary. And the whole mount in situ hybridization showed that it began to express in the middle third of the full-length primitive gut in 2-day larvae, where the hepatic caecum will form later during development. Phylogenetic analysis indicated that both amphioxus and ascidian trypsins are more closer to each other than to vertebrate trypsins, suggesting a continuous evolutionary divergence of vertebrate trypsins after split from protochordate/vertebrate common ancestor.

Antioxidant activities of recombinant amphioxus (Branchiostoma belcheri) apolipoprotein D

Apolipoprotein D (ApoD), a member of lipocalin, has been recently shown to be involved in regulating protection from oxidative stress. The absence of ApoD in mouse and Drosophila can reduce the resistance to oxidative stress and shorten lifespan. However, little information is available regarding the expression in vitro of ApoD and its biochemical properties. Amphioxus (Branchiostoma belcheri) ApoD, BbApoD, is an archetype of vertebrate ApoD proteins. In this study, the prokaryotic expression plasmid pET32a-BbApoD was constructed and recombinant BbApoD expressed in Escherichia coli BL21 and purified. Antioxidation assays showed that the recombinant BbApoD protein had the capacities to scavenge hydroxyl radicals (≥ 240 μg/ml) and to prevent nicking of the supercoiled DNA (≥ 100 μg/ml) in vitro, providing a biochemical evidence for antioxidant role of ApoD. This supports the notion that ApoD is part of the mechanisms regulating protection from oxidative stresses.