Major colour patterns of reef-building corals are due to a family of GFP-like proteins

Reef-building corals are renowned for their brilliant colours yet the bioch emical basis for the pigmentation of corals is unknown. Here, we show that these colours are due to a family of GFP-like proteins that fluoresce under ultraviolet (UV) or visible light. Pigments from ten coral species were al most identical to pocilloporin (Dove et al. 1995) being dimers or trimers w ith approximately 28-kDa subunits. Degenerative primers made to common N-te rminal sequences yielded a complete sequence from reef-building coral cDNA, which had 19.6% amino acid identity with green fluorescent protein (GFP). Molecular modelling revealed a 'beta -can' structure, like GFP, with 11 bet a -strands and a completely solvent-inaccessible fluorophore composed of th e modified residues Gln-61, Tyr-62 and Gly-63. The molecular properties of pocilloporins indicate a range of functions from the conversion of high-int ensity UV radiation into photosynthetically active radiation (PAR) that can be regulated by the dinoflagellate peridinin-chlorophyll-protein (PCP) com plex, to the shielding of the Soret and Q(x) bands of chlorophyll a and c f rom scattered high-intensity light. These properties of pocilloporin suppor t its potential role in protecting the photosynthetic machinery of the symb iotic dinoflagellates of corals under high light conditions and in enhancin g the availability of photosynthetic light under shade conditions.