Mycosporine-like amino acids

Mycosporine-like amino acids (MAAs) are small secondary metabolites produced by organisms that live in environments with high volumes of sunlight, usually marine environments. So far there are up to 20 known MAAs identified.^[1] They are commonly described as “microbial sunscreen” but their function is not limited to sun protection.

Background

MAAs are wide spread in the microbial world and have been reported in many microorganisms including heterotrophic bacteria, ^[2] cyanobacteria, ^[3] microalgae, ^[4] macroalgae, as well as some multi-cellular organisms. ^[5] Most research done on MAAs is on their light absorbing and radiation protecting properties. The first thorough description of MAAs was done in cyanobacteria living in a high UV radiation environment. ^[6] The major unifying characteristic among all MAAs is light absorption. All MAAs absorb UV light that can be destructive to biological molecules (DNA, Proteins, etc). Though most MAA research is done on their photo-protective capabilities, they are also multifunctional secondary metabolites that have many cellular functions. MAAs are effective antioxidant molecules and are able to stabilize free radicals within their ring structure. In addition to protecting cells from mutation via UV radiation and free radicals, MAAs are able to boost cellular tolerance to desiccation, salt stress, and heat stress.

Chemistry

Mycosporine–like amino acids are rather small molecules (<400Da). The structures of over 30 Mycosporine-like amino acids have been resolved and all contain a central cyclohexenone or cyclohexenimine ring and a wide variety of substitutions. ^[7] The ring structure is thought to absorb UV light and accommodate free radicals. All MAAs absorb ultraviolet light, typically between 310 and 340nm. ^[5] It is this light absorbing property that allows MAAs to protect cells from harmful UV radiation. Biosynthetic pathways of specific MAAs depend on the specific MAA and the organism that is producing it. These biosyenthetic pathways often share common enzymes and intermediates with other major biosynthetic pathways. An example of this is the shikimate pathway that is classically used to create phenylalanine; many intermediates and enzymes from this pathway are utilized in MAA synthesis.

Functions

Ultraviolet light responses

Protection from UV radiation

Ultraviolet UV-A and UV-B radiation is harmful to living systems. An important tool used to deal with UV exposure is the biosynthesis of small-molecule sunscreens. Mycosporine-like amino acids (MAAs) have been implicated in UV radiation protection. The genetic basis for this implication comes from the observed induction of MAA synthesis when organisms are exposed to UV radiation (between 280-400nm). Among many different organisms, this observation has occurred in aquatic yeasts,^[8] cyanobacteria,^[9] marine dinoflagellates,^[10] and some Antarctic diatoms.^[11] When MAAs absorb UV light the energy is dissipated as heat.^[12] UV-B photoreceptors have been identified in cyanobacteria as the molecules responsible for the UV light induced responses, including synthesis of MAAs.^[13]

Protection from oxidative damage

Some MAAs also protect cells from reactive oxygen species (i.e. singlet oxygen, superoxide anions, hydroperoxyl radicals, and hydroxyl radicals).^[11] Reactive oxygen species can be created during photosynthesis; further supporting the idea that MAAs provide protection from UV light. Mycosporine-glycine is a MAA that provides antioxidant protection even before Oxidative stress response genes and [antioxidant]] enzymes are induced. ^[14][15] MAA-glycine (mycosporine-glycine) is able to quench singlet oxygen and hydroxyl radicals very quickly and efficiently. ^[16] Some oceanic microbial ecosystems are exposed to high concentrations of oxygen and intense light; these conditions are likely to generate high levels of reactive oxygen species. In these ecosystems, MAA-rich cyanobacteria may be providing antioxidant activity. ^[17]

Accessory pigments in photosynthesis

MAAs are able to absorb UV light. A study published in 1976 demonstrated that an increase in MAA content was associated with an increase in photosynthetic respiration.^[18] Further studies done in marine cyanobacteria showed that the MAAs synthesized in response to UV-B correlated with an increase in photosynthetic pigments.^[19] Though not absolute proof, these findings do implicate MAAs as accessory pigments to photosynthesis.

Environmental stress responses

Salt stress

Osmotic stress is defined as difficulty maintaining proper fluids in the cell within a hypertonic or hypotonic environment. MAAs accumulate within a cell’s cytoplasm and contribute to the osmotic pressure within a cell, thus relieving pressure from salt stress in a hypertonic environment.^[11] As evidence of this, MAAs are seldom found in large quantities in cyanobacteria (bacteria that live in freshwater environments). However in saline and hypertonic environments, cyanobacteria often contain high concentrations of MAAs .^[20] But, the concentration of MAAs within cells living in hyper-saline environments is far from the amount required to balance the salinity. Therefore additional osmotic solutes must be present as well.

Desiccation stress

Desiccation (drought) stress is defined as conditions where water becomes the growth limiting factor. MAAs have been reportedly found in high concentrations in many microorganisms exposed to drought stress.^[21] Particularly cyanobacteria species that are exposed to desiccation, UV radiation and oxidation stress have been shown to possess MAA’s in an extracellular matrix.^[22] However it has been shown that MAAs do not provide sufficient protection against high doses of UV radiation. ^[3]

Thermal stress

Thermal (heat) stress is defined as temperatures lethal or inhibitory towards growth. MAA concentrations have been shown to be up-regulated when an organism is under thermal stress.^[23][24] Multipurpose MAAs could also be compatible solutes under freezing conditions, because a high incidence of MAA producing organisms have been reported in cold aquatic environments.^[11]

Further reading

• Bandaranayake WM (1998) Mycosporines: are they nature’s sunscreens? Natural Product Reports 1998: 159-171.
• Eric W. Schmidt (2011) An Enzymatic Route to Sunscreens. ChemBioChem 12: 3.
• Rajesh P. Rastogi, Richa, Rajeshwar P. Sinha, Shailendra P. Singh, Donat-P. Häder, Photoprotective compounds from marine organisms, Journal of Industrial Microbiology & Biotechnology, 2010, 37, 6, 537
• Rozema J, Bjorn LO, Bornman JF et al. (2002) The role of UV-B radiation in aquatic and terrestrial ecosystems – an experimental and functional analysis of the evolution of UV-absorbing compounds. J photochem Photobiol B 66: 2-12.
• Shailendra P. Singh, Manfred Klisch, Rajeshwar P. Sinha, Donat-P. Häder, Effects of Abiotic Stressors on Synthesis of the Mycosporine-like Amino Acid Shinorine in the Cyanobacterium Anabaena variabilis PCC 7937, Photochemistry and Photobiology, 2008, 84, 6
• Sinha RP, Klish M, Groninger A & Hader D-P (1998) Ultraviolet-absorbing/screening substances in cyanobacteria, phytoplankton and macroalgae. J Photochem Photobiol B 47: 83-94.
• Yangqiao Zheng, Kunshan Gao, IMPACTS OF SOLAR UV RADIATION ON THE PHOTOSYNTHESIS, GROWTH, AND UV-ABSORBING COMPOUNDS IN GRACILARIA LEMANEIFORMIS (RHODOPHYTA) GROWN AT DIFFERENT NITRATE CONCENTRATIONS, Journal of Phycology, 2009, 45, 2
• Zhiguang Xu, Kunshan Gao, Impacts of UV radiation on growth and photosynthetic carbon acquisition inGracilaria lemaneiformis(Rhodophyta) under phosphorus-limited and replete conditions, Functional Plant Biology, 2009, 36, 12, 1057

External links

• "MYCOSPORINE-LIKE AMINO ACIDS AND RELATED GADUSOLS" - Annual Review of Physiology
• "Mycosporines and mycosporine-like amino acids: UV protectants or multipurpose secondary metabolites?" - InterScience
• "Mycosporine-Like Amino Acids and Marine Toxins" - Marine Drugs
• "Sources of mycosporine-like amino acids in planktonic Chlorella-bearing ciliates (Ciliophora)" - PubMed Central
• "Mycosporine-like amino acids in the marine dinoflagellate Gyrodinium dorsum: induction by ultraviolet irradiation" - Photobiology
• "The Role of Mycosporine-Like Amino Acids (MAAs) in Harmful Bloom-Forming Dinoflagellates: Effects of Ultraviolet Radiation, Vertical Mixing, and Nutrient Availability" - National Center for Environmental Research
• "Mycosporine-like amino acids" - International Journal
• "Antioxidant activity of mycosporine-like amino acids isolated from three red macroalgae and one marine lichen" - SpringerLink
• http://microbewiki.kenyon.edu/index.php/The_Responses_of_Cyanobacteria_to_UV-B_Irradiation

References and Notes

1. ^ Cardozo et al. 2007. Metabolites from algae with economical impact. Comparative Biochemistry and Physiology Part C: Toxicology & Pharmacology, Volume 146, Issues 1-2, July-August 2007, Pages 60-78.
2. ^ Arai, Takayuki. Nishijima, Miyuki. Adachi, Kyoko. Sano, Hiroshi. 1992. Isolation and structure of a UV absorbing substance from the marine bacterium Micrococcus sp. MBI Report.
3. ^ ^{a b} Garcia-Pichel, and Richard W. Castenholz. 1993. Occurrence of UV-Absorbing, Mycosporine-Like Compounds among Cyanobacterial Isolates and an Estimate of Their Screening Capacity. Appl Environ Microbiology. 59(1): 163-169
4. ^ Okaichi T, Tokumura T. Isolation of cyclohexene derivatives from Noctiluca miliaris. 1980 Chemical Society of Japan
5. ^ ^{a b} Rezanka T, Temina M, Tolstikov AG, Dembitsky VM, 2004. Natural Microbial UV Radiation Filters – Mycosporine-like Amino Acids. Folia Microbiology. 49 (4). 339-352.
6. ^ Garcia-Pichel F, Wingard CE, Castenholz RW. 1993. Evidence Regarding the UV Sunscreen Role of a Mycosporine-Like Compound in the Cyanobacterium Gloeocapsa sp. Appl Environ Microbiol. 59(1):170-6.
7. ^ Bandaranayake WM. 1998. Mycosporines: are they nature’s sunscreens? Natural Product Reports. 159–171.
8. ^ Libkind D, Perez PA, Sommaruga R, Díeguez MC, Ferraro M, Brizzio S, Zagarese H & Rosa Giraudo MR (2004) Constitutive and UV-inducible synthesis of photoprotective compounds (carotenoids and mycosporines) by freshwater yeasts. Photochem Photobiol Sci 3: 281–286.
9. ^ Portwich A & Garcia-Pichel F (1999) Ultraviolet and osmotic stresses induce and regulate the synthesis of mycosporines in the cyanobacterium Chlorogloeopsis PCC 6912. Arch Microbiol 172: 187–192.
10. ^ Neale PJ, Banaszak AT & Jarriel CR (1998) Ultraviolet sunscreens in Gymnodinium sanguineum (Dinophyceae): mycosporine-like amino acids protect against inhibition of photosynthesis. J Phycol 34: 928–938.
11. ^ ^{a b c d} Oren A & Gunde-Cimerman N. (2007). Mycosporines and mycosporine-like amino acids: UV protectants or multipurpose secondary metabolites? FEMS Microbiol. Lett 269: 1-10.
12. ^ http://esraa-chemist.blogspot.com/2011_02_01_archive.html
13. ^ Portwich A & Garcia-Pichel F (2000) A novel prokaryotic UVB photoreceptor in the cyanobacterium Chlorogloeopsis PCC 6912. Photochem Photobiol 71: 493–498.
14. ^ Yakovleva I, Bhagooli R, Takemura A & Hidaka M (2004) Differential susceptibility to oxidative stress of two scleractinian corals: antioxidant functioning of mycosporine-glycine. Comp Biochem Physiol B 139: 721-730
15. ^ Suh H-J, Lee H-W & Jung J (2003) Mycosporine glycine protects biological systems against photodynamic damage by quenching singlet oxygen with a high efficiency. Photochem Photobiol 78: 109-113.
16. ^ Dunlap WC & Yamamoto Y (1995) Small-molecule antioxidants in marine organisms: antioxidant activity of mycosporine-glycine. Comp Biochem Physiol B 112: 105-114.
17. ^ Canfield DE, Sorensen KB & Oren A (2004) Biogeochemistry of a gypsum-encrusted microbial ecosystem. Geobiology 2: 133-150.
18. ^ Sivalingam PM, Ikawa T & Nisizawa K (1976) Physiological roles of a substance 334 in algae. Bot Mar 19: 9-21.
19. ^ Bhandari R & Sharma PK (2007) Effect of UV-B and high visual radiation on photosynthesis in freshwater (nostoc spongiaeforme) and marine (Phormidium corium) cyanobacteria. Indian J Biochem Biophys 44(4):231-9.
20. ^ Oren, A. (1997). Mycosporine-like amino acids as osmotic solutes in a community of halophilic cyanobacteria. Geomicrobiology Journal, 14(3), 231-240.
21. ^ Wright, D. (2005). Uv irradiation and desiccation modulate the three-dimensional extracellular matrix of nostoc commune (cyanobacteria). The Journal of Biological Chemistry, 280(1), 40271-40281.
22. ^ Tirkey, J., & Adhikary, S.P. (2005). Cyanobacteria in biological soil crusts of india. Current Science , 89(3), 515-521.
23. ^ Michalek-Wagner, K., & Willis, B.L. (2001). Impacts of bleaching on the soft coral lobophytum compactum. ii. biochemical changes in adults and their eggs. Coral Reefs, 19(3), 240-246.
24. ^ Dunlap WC & Shick JM (1998) Ultraviolet radiation-absorbing mycosporine-like amino acids in coral reef organisms: a biochemical and environmental perspective. J Phycol 34: 418-430.

Note: This article was compiled as part of the Colorado State University, Microbial Physiology class of Spring 2011.