Project description:An enzyme with sarcosine dimethylglycine methyltransferase (SDMT) activity has been identified in the thermophilic eukaryote, Galdieria sulphuraria. The crystal structure of the enzyme, solved to a resolution of 1.95 A, revealed a fold highly similar to that of mycolic acid synthases. The kcat and apparent K(M) values were 64.3 min(-1) and 2.0 mM for sarcosine and 85.6 min(-1) and 2.8 mM for dimethylglycine, respectively. Apparent K(M) values of S-adenosylmethionine were 144 and 150 microM for sarcosine and dimethylglycine, respectively, and the enzyme melting temperature was 61.1 degrees C. Modeling of cofactor binding in the active site based on the structure of methoxy mycolic acid synthase 2 revealed a number of conserved interactions within the active site.
Project description:BACKGROUND:Genome reduction in intracellular pathogens and endosymbionts is usually compensated by reliance on the host for energy and nutrients. Free-living taxa with reduced genomes must however evolve strategies for generating functional diversity to support their independent lifestyles. An emerging model for the latter case is the Rhodophyta (red algae) that comprises an ecologically widely distributed, species-rich phylum. Red algae have undergone multiple phases of significant genome reduction, including extremophilic unicellular taxa with limited nuclear gene inventories that must cope with hot, highly acidic environments. RESULTS:Using genomic data from eight red algal lineages, we identified 155 spliceosomal machinery (SM)-associated genes that were putatively present in the red algal common ancestor. This core SM gene set is most highly conserved in Galdieria species (150 SM genes) and underwent differing levels of gene loss in other examined red algae (53-145 SM genes). Surprisingly, the high SM conservation in Galdieria sulphuraria coincides with the enrichment of spliceosomal introns in this species (2 introns/gene) in comparison to other red algae (<?0.34 introns/gene). Spliceosomal introns in G. sulphuraria undergo alternatively splicing, including many that are differentially spliced upon changes in culture temperature. CONCLUSIONS:Our work reveals the unique nature of G. sulphuraria among red algae with respect to the conservation of the spliceosomal machinery and introns. We discuss the possible implications of these findings in the highly streamlined genome of this free-living eukaryote.
Project description:The ACT domain is a structurally conserved small molecule binding domain which is mostly involved in amino acid and purine metabolism. Here, we report the crystal structure of a tandem ACT domain-containing protein (ACTP) from Galdieria sulphuraria. The two ACTP monomers in the asymmetric unit form a dimer with a non-crystallographic twofold axis in a domain-swapped manner, showing a horseshoe-like structure with a central crevice. This structure contributes to expand our knowledge on the structural diversity of ACT domain-containing proteins.
Project description:Photosystem I-light harvesting complex I (PSI-LHCI) was isolated from the thermoacidophilic red alga Galdieria sulphuraria, and its structure, composition, and light-harvesting function were characterized by electron microscopy, mass spectrometry, and ultrafast optical spectroscopy. The results show that Galdieria PSI is a monomer with core features similar to those of PSI from green algae, but with significant differences in shape and size. A comparison with the crystal structure of higher plant (pea) PSI-LHCI indicates that Galdieria PSI binds seven to nine light-harvesting proteins. Results from ultrafast optical spectroscopy show that the functional coupling of the LHCI proteins to the PSI core is tighter than in other eukaryotic PSI-LHCI systems reported thus far. This tight coupling helps Galdieria perform efficient light harvesting under the low-light conditions present in its natural endolithic habitat.
Project description:We have isolated ribulose-1,5-bisphosphate-carboxylase/oxygenase (RUBISCO) from the red algae Galdieria Sulphuraria. The protein crystallized in two different crystal forms, the I422 crystal form being obtained from high salt and the P21 crystal form being obtained from lower concentration of salt and PEG. We report here the crystallization, preliminary stages of structure determination and the detection of the structural phase transition in the P21 crystal form of G. sulphuraria RUBISCO. This red algae enzyme belongs to the hexadecameric class (L8S8) with an approximate molecular weight 0.6MDa. The phase transition in G. sulphuraria RUBISCO leads from two hexadecamers to a single hexadecamer per asymmetric unit. The preservation of diffraction power in a phase transition for such a large macromolecule is rare.
Project description:Nuclear genome sequencing from extremophilic eukaryotes has revealed clues about the mechanisms of adaptation to extreme environments, but the functional consequences of extremophily on organellar genomes are unknown. To address this issue, we assembled the mitochondrial and plastid genomes from a polyextremophilic red alga, Galdieria sulphuraria strain 074 W, and performed a comparative genomic analysis with other red algae and more broadly across eukaryotes. The mitogenome is highly reduced in size and genetic content and exhibits the highest guanine-cytosine skew of any known genome and the fastest substitution rate among all red algae. The plastid genome contains a large number of intergenic stem-loop structures but is otherwise rather typical in size, structure, and content in comparison with other red algae. We suggest that these unique genomic modifications result not only from the harsh conditions in which Galdieria lives but also from its unusual capability to grow heterotrophically, endolithically, and in the dark. These conditions place additional mutational pressures on the mitogenome due to the increased reliance on the mitochondrion for energy production, whereas the decreased reliance on photosynthesis and the presence of numerous stem-loop structures may shield the plastome from similar genomic stress.
Project description:Galdieria sulphuraria and Cyanidioschyzon merolae are thermo-acidophilic unicellular red algal cousins capable of living in volcanic environments, although the former can additionally thrive in the presence of toxic heavy metals. Bioinformatic analyses of transport systems were carried out on their genomes, as well as that of the mesophilic multicellular red alga Chondrus crispus (Irish moss). We identified transport proteins related to the metabolic capabilities, physiological properties, and environmental adaptations of these organisms. Of note is the vast array of transporters encoded in G. sulphuraria capable of importing a variety of carbon sources, particularly sugars and amino acids, while C. merolae and C. crispus have relatively few such proteins. Chondrus crispus may prefer short chain acids to sugars and amino acids. In addition, the number of encoded proteins pertaining to heavy metal ion transport is highest in G. sulphuraria and lowest in C. crispus. All three organisms preferentially utilize secondary carriers over primary active transporters, suggesting that their primary source of energy derives from electron flow rather than substrate-level phosphorylation. Surprisingly, the percentage of inorganic ion transporters encoded in C. merolae more closely resembles that of C. crispus than G. sulphuraria, but only C. crispus appears to signal via voltage-gated cation channels and possess a Na+ /K+ -ATPase and a Na+ exporting pyrophosphatase. The results presented in this report further our understanding of the metabolic potential and toxic compound resistances of these three organisms.