Mycosporine-like amino acids (MAAs) profile of a rice-field cyanobacterium Anabaena doliolum as influenced by PAR and UVR

The mycosporine-like amino acid (MAA) profile of a rice-field cyanobacterium, Anabaena doliolum, was studied under PAR and PAR + UVR conditions. The high-performance liquid chromatographic analysis of water-soluble compounds reveals the biosynthesis of three MAAs, mycosporine-glycine (lambda (max) = 310 nm), porphyra-334 (lambda (max) = 334 nm) and shinorine (lambda (max) = 334 nm), with retention times of 4.1, 3.5 and 2.3 min, respectively. This is the first report for the occurrence of mycosporine-glycine and porphyra-334 in addition to shinorine in Anabaena strains studied so far. The results indicate that mycosporine-glycine (monosubstituted) acts as a precursor for the biosynthesis of the bisubstituted MAAs shinorine and porphyra-334. Mycosporine-glycine was under constitutive control while porphyra-334 and shinorine were induced by UV-B radiation, indicating the involvement of UV-regulated enzymes in the biotransformation of MAAs. It seems that A. doliolum is able to protect its cell machinery from UVR by synthesizing a complex set of MAAs and thus is able to survive successfully during the summer in its natural brightly lit habitats.     

The distribution of mycosporine-like amino acids (MAAs) and the phylogenetic identity of symbiotic dinoflagellates in cnidarian hosts from the Mexican Caribbean

A survey of 54 species of symbiotic cnidarians that included hydrozoan corals, anemones, gorgonians and scleractinian corals was conducted in the Mexican Caribbean for the presence of mycosporine-like amino acids (MAAs) in the host as well as the Symbiodinium fractions. The host fractions contained relatively simple MAA profiles, all harbouring between one and three MAAs, principally mycosporine-glycine followed by shinorine and porphyra-334 in smaller amounts. Symbiodinium populations were identified to sub-generic levels using PCR-DGGE analysis of the Internal Transcribed Spacer 2 (ITS2) region. Regardless of clade identity, all Symbiodinium extracts contained MAAs, in contrast to the pattern that has been found in cultures of Symbiodinium, where clade A symbionts produced MAAs whereas clade B, C, D, and E symbionts did not. Under natural conditions between one and four MAAs were identified in the symbiont fractions, mycosporine-glycine (λ_max = 310 nm), shinorine (λ_max = 334 nm), porphyra-334 (λ_max = 334 nm) and palythine (λ_max = 320 nm). One sample also contained mycosporine-2-glycine (λ_max = 331 nm). These data suggest that Symbiodinium is restricted to producing five MAAs and there also appears to be a defined order of appearance of these MAAs: mycosporine-glycine followed by shinorine (in one case mycosporine-2-glycine), then porphyra-334 and palythine. Overall, mycosporine-glycine was found in highest concentrations in the host and symbiont extracts. This MAA, unlike many other MAAs, absorbs within the ultraviolet-B range (UVB, 280-320 nm) and is also known for moderate antioxidant properties thus potentially providing protection against the direct and indirect effects of UVR. No depth-dependent changes could be identified due to a high variability of MAA concentrations when all species were included in the analysis. The presence of at least one MAA in all symbiont and host fractions analyzed serves to highlight the importance of MAAs, and in particular the role of mycosporine-glycine, as photoprotectants in the coral reef environment.     

Evidence from directed mutagenesis that positively charged amino acids are necessary for interaction of nitrogenase with the [2Fe-2S) heterocyst ferredoxin (FdxH) from the cyanobacterium Anabaena sp., PCC7120

Sequence comparison of the heterocyst-type ferredoxin (FdxH) from Anabaena 7120 and type-I ferredoxins (PetF) from the same organism and other cyanobacteria revealed a group of positively charged residues characteristic for FdxH. Molecular modeling showed that these basic amino acids are clustered on the surface of FdxH. The corresponding domain of PetF contained acidic or nonpolar residues instead. To identify amino acids that are important for interaction with nitrogenase, we generated site-directed mutations in the fdxH gene and assayed the in vitro activity of the resulting recombinant proteins isolated from Escherichia coli. In addition to the point mutants, two chimeric proteins, FdxH : PetF and PetF : FdxH, were constructed containing the 58 N-terminal amino acids of one ferredoxin fused to the 40 C-terminal amino acids of the other. Exchange of lysines 10 and 11 of FdxH for the corresponding residues of PetF (glutamate 10 and alanine 11) resulted in a ferredoxin with greatly decreased affinity to nitrogenase. This indicates an important function of these basic amino acids in interaction with dinitrogenase reductase (NifH) from Anabaena. In addition we checked the reactivity of the recombinant ferredoxins with ferredoxin-NADP⁺ oxidoreductase (FNR) and photosystem I. The experiments with both the chimeric and point mutated ferredoxins showed that the C-terminal part of this protein determines its activity in NADP⁺ photoreduction.