A gene encoding a fluorescent protein from the stony coral Lobophyllia hemprichii has been cloned in Escherichia coli and characterized by biochemical and biophysical methods. The protein, which we named EosFP, emits strong green fluorescence (516 nm) that changes to red (581 nm) upon near-UV irradiation at Ϸ390 nm because of a photo-induced modification involving a break in the peptide backbone next to the chromophore. Single-molecule fluorescence spectroscopy shows that the wild type of EosFP is tetrameric, with strong Fö rster resonance coupling among the individual fluorophores. We succeeded in breaking up the tetramer into AB and AC subunit dimers by introducing the single point mutations V123T and T158H, respectively, and the combination of both mutations yielded functional monomers. Fusion constructs with a variety of proteins were prepared and expressed in human cells, showing that normal biological functions were retained. The possibility to locally change the emission wavelength by focused UV light makes EosFP a superb marker for experiments aimed at tracking the movements of biomolecules within the living cell.

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A variety of genetically encoded reporters use changes in fluorescence (or Förster) resonance energy transfer (FRET) to report on biochemical processes in living cells. The standard genetically encoded FRET pair consists of cyan and yellow fluorescent proteins (CFP and YFP), but many CFP-YFP reporters suffer from low FRET dynamic range, phototoxicity from the CFP excitation light, and complex photokinetic events such as reversible photobleaching and photoconversion. Here, we engineered two fluorescent proteins, Clover and mRuby2, which are the brightest green and red fluorescent proteins to date, and have the highest Förster radius of any ratiometric FRET pair yet described. Replacement of CFP and YFP in reporters of kinase activity, small GTPase activity, and transmembrane voltage significantly improves photostability, FRET dynamic range, and emission ratio changes. These improvements enhance detection of transient biochemical events such as neuronal action potential firing and RhoA activation in growth cones.

Corals are animals that form close mutualistic associations with endosymbiotic photosynthetic algae of the genus Symbiodinium. Together they provide the calcium carbonate framework of coral reef ecosystems. The importance of the microbiome (i.e., bacteria, archaea, fungi, and viruses) to holobiont functioning has only recently been recognized. Given that growth and density of Symbiodinium within the coral host is highly dependent on nitrogen availability, nitrogen-cycling microbes may be of fundamental importance to the stability of the coral-algae symbiosis and holobiont functioning, in particular under nutrient-enriched and -depleted scenarios. We summarize what is known about nitrogen cycling in corals and conclude that disturbance of microbial nitrogen cycling may be tightly linked to coral bleaching and disease.

GFP-like fluorescent proteins (FPs) are the key color determinants in reef-building corals (class Anthozoa, order Scleractinia) and are of considerable interest as potential genetically encoded fluorescent labels. Here we report 40 additional members of the GFP family from corals. There are three major paralogous lineages of coral FPs. One of them is retained in all sampled coral families and is responsible for the non-fluorescent purple-blue color, while each of the other two evolved a full complement of typical coral fluorescent colors (cyan, green, and red) and underwent sorting between coral groups. Among the newly cloned proteins are a “chromo-red” color type from Echinopora forskaliana (family Faviidae) and pink chromoprotein from Stylophora pistillata (Pocilloporidae), both evolving independently from the rest of coral chromoproteins. There are several cyan FPs that possess a novel kind of excitation spectrum indicating a neutral chromophore ground state, for which the residue E167 is responsible (numeration according to GFP from A. victoria). The chromoprotein from Acropora millepora is an unusual blue instead of purple, which is due to two mutations: S64C and S183T. We applied a novel probabilistic sampling approach to recreate the common ancestor of all coral FPs as well as the more derived common ancestor of three main fluorescent colors of the Faviina suborder. Both proteins were green such as found elsewhere outside class Anthozoa. Interestingly, a substantial fraction of the all-coral ancestral protein had a chromohore apparently locked in a non-fluorescent neutral state, which may reflect the transitional stage that enabled rapid color diversification early in the history of coral FPs. Our results highlight the extent of convergent or parallel evolution of the color diversity in corals, provide the foundation for experimental studies of evolutionary processes that led to color diversification, and enable a comparative analysis of structural determinants of different colors.

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We performed the biochemical and biophysical characterization of a red fluorescent protein, eqFP611, from the sea anemone Entacmaea quadricolor cloned in Escherichia coli. With an excitation maximum at 559 nm and an emission maximum at 611 nm, the recombinant protein shows the most red-shifted emission and the largest Stokes shift of all nonmodified proteins in the green fluorescent protein family. The protein fluoresces with a high quantum yield of 0.45, although it resembles the nonfluorescent members of this protein class, as inferred from the absence of the key amino acid serine at position 143. Fluorescence is constant within the range pH 4 -10. Red fluorophore maturation reaches a level of 90% after Ϸ12 h by passing through a green intermediate. After complete maturation, only a small fraction of the green species (less than 1%) persists. The protein has a reduced tendency to oligomerize, as shown by its monomeric appearance in SDS͞ PAGE analysis and single-molecule experiments. However, it forms tetramers at higher concentrations in the absence of detergent. Fluorescence correlation spectroscopy reveals light-driven transitions between bright and dark states on submillisecond and millisecond time scales. Applicability of eqFP611 for in vivo labeling in eukaryotic systems was shown by expression in a mammalian cell culture.G reen fluorescent protein from Aequorea victoria (avGFP) and its derivatives have become extremely popular in life science research as protein labels, markers of gene expression, and reporters of environmental conditions in living cells (1-3). Molecular properties of avGFP have been modified by sitedirected mutagenesis to optimize their applicability. Still, some properties, most importantly the restricted range of emission wavelengths, pose severe limitations in certain applications. In particular, red fluorescent proteins (FP) would be highly desirable because of the reduced cellular autofluorescence in the red spectral range and for use in multicolor labeling or fluorescence resonance energy transfer experiments. Efforts to produce stable red-fluorescent avGFP variants have not yet met with success. Recently, however, avGFP homologs were discovered in nonbioluminescent Anthozoa species (4-8). Some of the Anthozoa FPs show spectral properties that deviate greatly from avGFP, including red-emitting variants.One of them, a red FP from the corallimorpharian Discosoma sp. named drFP583 (6), commercially known as DsRed, became the subject of various biochemical and biophysical studies (9-12). These studies revealed detrimental properties for certain applications of the wild-type protein, especially the slow and incomplete maturation of the fluorophore, the obligate formation of tetramers, and the tendency to aggregate. Meanwhile, maturation properties have been greatly improved by engineering the protein, and the tendency to form aggregates was also reduced by mutagenesis (13-15). Recently, the oligomerization problem of DsRed has been solved by mutagenetic means (16).We have continued ...

Coral reefs are in rapid decline on a global scale due to human activities and a changing climate. Shallow water reefs depend on the obligatory symbiosis between the habitat forming coral host and its algal symbiont from the genus Symbiodinium (zooxanthellae). This association is highly sensitive to thermal perturbations and temperatures as little as 1°C above the average summer maxima can cause the breakdown of this symbiosis, termed coral bleaching. Predicting the capacity of corals to survive the expected increase in seawater temperatures depends strongly on our understanding of the thermal tolerance of the symbiotic algae. Here we use molecular phylogenetic analysis of four genetic markers to describe Symbiodinium thermophilum, sp. nov. from the Persian/Arabian Gulf, a thermally tolerant coral symbiont. Phylogenetic inference using the non-coding region of the chloroplast psbA gene resolves S. thermophilum as a monophyletic lineage with large genetic distances from any other ITS2 C3 type found outside the Gulf. Through the characterisation of Symbiodinium associations of 6 species (5 genera) of Gulf corals, we demonstrate that S. thermophilum is the prevalent symbiont all year round in the world's hottest sea, the southern Persian/Arabian Gulf.