Coral Fluorescent Proteins as Antioxidants

Abstract

BackgroundA wide array of fluorescent proteins (FP) is present in anthozoans, although their biochemical characteristics and function in host tissue remain to be determined. Upregulation of FP's frequently occurs in injured or compromised coral tissue, suggesting a potential role of coral FPs in host stress responses.Methodology/Principal FindingsThe presence of FPs was determined and quantified for a subsample of seven healthy Caribbean coral species using spectral emission analysis of tissue extracts. FP concentration was correlated with the in vivo antioxidant potential of the tissue extracts by quantifying the hydrogen peroxide (H2O2) scavenging rates. FPs of the seven species varied in both type and abundance and demonstrated a positive correlation between H2O2 scavenging rate and FP concentration. To validate this data, the H2O2 scavenging rates of four pure scleractinian FPs, cyan (CFP), green (GFP), red (RFP) and chromoprotein (CP), and their mutant counterparts (without chromophores), were investigated. In vitro, each FP scavenged H2O2 with the most efficient being CP followed by equivalent activity of CFP and RFP. Scavenging was significantly higher in all mutant counterparts.Conclusions/SignificanceBoth naturally occurring and pure coral FPs have significant H2O2 scavenging activity. The higher scavenging rate of RFP and the CP in vitro is consistent with observed increases of these specific FPs in areas of compromised coral tissue. However, the greater scavenging ability of the mutant counterparts suggests additional roles of scleractinian FPs, potentially pertaining to their color. This study documents H2O2 scavenging of scleractinian FPs, a novel biochemical characteristic, both in vivo across multiple species and in vitro with purified proteins. These data support a role for FPs in coral stress and immune responses and highlights the multi-functionality of these conspicuous proteins.

Fluorescent proteins in dominant mesophotic reef-building corals

“…Photoprotection, the processes and mechanisms to prevent damage from light, is important for both the coral as well as Symbiodinium. Photoprotection by FPs could include absorbing, screening, and scattering light as well as acting as an antioxidant (Salih et al 2000, Gilmore et al 2003, Bou-Abdallah et al 2006, Palmer et al 2009a. Ultraviolet radiation, PAR, and to a lesser extent blue light (~410−480 nm) are greatly reduced at mesophotic depths (Kirk 1994, Kahng et al 2012, the present study).…”

“…FPs may also be able to act as antioxidants, which scavenge and neutralize reactive oxygen species (Mazel et al 2003, Bou-Abdallah et al 2006, Palmer et al 2009a. Reactive oxygen species can damage proteins, lipids, and DNA (Lesser 2006).…”

“…While reef-building corals have the capacity to produce significant quantities of FPs (Leutenegger et al 2007), the function of FPs is unknown. As a result of ambiguous data which may be caused by the diversity of FPs and corals, hypothesized roles for the function of FPs include photoprotection (Salih et al 2000, Roth et al 2010, Smith et al 2013, antioxidant activity (Mazel et al 2003, Bou-Abdallah et al 2006, Palmer et al 2009a), photosynthesis enhancement (Salih et al 2000), Symbiodinium regulation (Field et al 2006), part of an immune response (Palmer et al 2009b, D'Angelo et al 2012, camouflage (Matz et al 2006b), maintenance of color diversity (Dove et al 2001), and attraction of free-living Symbiodinium (Hollingsworth et al 2004). It is possible that different FPs could have different roles, particularly in distinct environments such as shallow or mesophotic habitats.…”

Green fluorescent protein regulation in the coral Acropora yongei during photoacclimation

“…Hypothesized roles for FPs include photoprotection (Kawaguti, 1944;Salih et al, 2000), photosynthesis enhancement (Kawaguti, 1969), camouflage , antioxidant (BouAbdallah et al, 2006;Palmer et al, 2009b), regulation of symbiotic dinoflagellates Field et al, 2006) and as part of the coral immune response (Palmer et al, 2009a). Corals produce a number of FPs with different spectral properties (Alieva et al, 2008), including FPs that do not emit visible fluorescence, which are often called pocilloporins or GFP-like proteins (Dove et al, 1995;Dove et al, 2001).…”

Method for Determining the Contribution of Fluorescence to an Optical Signature, with Implications for Postulating a Visual Function

“…Much of this has focused on origin and possible ecophysiological roles of the fluorescing proteins in reef corals (Salih et al, 2000;Kelmanson and Matz, 2003;Ugalde et al, 2004;Bou-Abdallah et al, 2006;Palmer et al, 2009;Gittins et al, 2015;Smith et al, 2017), but some studies have touched on possible visual functions in fish and other marine organisms (Mazel et al, 2004;Haddock et al, 2005;Matz et al, 2006;Michiels et al, 2008;Gerlach et al, 2014;Sparks et al, 2014;Haddock and Dunn, 2015;Gruber et al, 2016). A few of these latter have had a strong foundation in measurement and analysis, while others have been more speculative and suggestive, based purely on observation and correlation.…”