Mar. Drugs 2025, 23(11), 441; https://doi.org/10.3390/md23110441 (registering DOI) - 16 Nov 2025
Abstract
Although marine sponges display strikingly diverse colors, the molecular basis of this color diversity remains largely unknown. Recently, the blue coloration of Haliclona sp. was attributed to a water-soluble carotenoprotein that binds orange astaxanthin (AXT) and mytiloxanthin (MXT) and belongs to the ependymin
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Although marine sponges display strikingly diverse colors, the molecular basis of this color diversity remains largely unknown. Recently, the blue coloration of Haliclona sp. was attributed to a water-soluble carotenoprotein that binds orange astaxanthin (AXT) and mytiloxanthin (MXT) and belongs to the ependymin superfamily. Here, we investigated the coloration mechanism of a purple sponge, Haliclona sp. The purified purple protein was identified as a secreted glycoprotein, representing the second example of a color protein belonging to the ependymin superfamily. The blue and purple proteins were accordingly designated carotenoependymin (Cep)-Blue1 and Cep-Purple1. Cep-Blue1 binds orange AXT and MXT in a 1:1 ratio, whereas Cep-Purple1 binds only AXT, producing a smaller red shift than Cep-Blue1 in the 550–750 nm range. In vitro reconstitution of carotenoid-free apoproteins with their native carotenoids reproduced the original spectra. When the carotenoids bound to Cep-Blue1 and Cep-Purple1 were exchanged and reconstituted in vitro, Cep-Blue1 reconstituted with AXT exhibited a purplish-blue color, whereas Cep-Purple1 reconstituted with an equimolar mixture of AXT and MXT showed a preference for AXT and displayed an incomplete red shift. These results suggest that the subtle color variations among Haliclona species are determined by both species-specific carotenoid composition and the structural features of carotenoependymin proteins.
Full article
(This article belongs to the Special Issue Marine Carotenoids: Properties, Health Benefits, and Applications)
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