Differential expression of the demosponge (Suberites domuncula) carotenoid oxygenases in response to light: protection mechanism against the self-produced toxic protein (Suberitine).

ABSTRACT: The demosponge Suberites domuncula has been described to contain high levels of a proteinaceous toxin, Suberitine, that displays haemolytic activityIn the present study this 7-8 kDa polypeptide has been isolated and was shown to exhibit also cytotoxic effects on cells of the same species. Addition of retinal, a recently identified metabolite of ?-carotene that is abundantly present in S. domuncula was found to reduce both the haemolytic and the cell toxic activity of Suberitine at a molar ratio of 1:1. Spectroscopic analyses revealed that the interaction between ?-carotene and Suberitine can be ascribed to a reversible energy transfer reaction. The enzyme that synthesises retinal in the sponge system is the ?,?-carotene-15,15'-dioxygenase [carotene dioxygenase]. In order to clarify if this enzyme is the only ?-carotene-metabolizing enzyme a further oxygenase had been identified and cloned, the (related) carotenoid oxygenase. In contrast to the dioxygenase, the carotenoid oxygenase could not degrade ?-carotene or lycopene in Escherichia coli strains that produced these two carotenoids; therefore it had been termed related-carotenoid oxygenase. Exposure of primmorphs to light of different wavelengths from the visible spectrum resulted after 3 days in a strong upregulation of the dioxygenase in those 3D-cell aggregates that had been incubated with ?-carotene. The strongest effect is seen with blue light at a maximum around 490 nm. It is concluded that the toxin Suberitine is non-covalently modified by retinal, the cleavage product from ?-carotene via the enzyme carotene dioxygenase, a light inducible oxygenase. Hence, this study highlights that in S. domuncula the bioactive metabolite, retinal, has the property to detoxify its homologous toxin.

SUBMITTER: Muller WE 

PROVIDER: S-EPMC3280542 | biostudies-literature | 2012 Jan

REPOSITORIES: biostudies-literature