Evolution of Linoleic Acid Biosynthesis Paved the Way for Ecological Success of Termites.

Termites are dominant animals of tropical terrestrial ecosystems. Their success is due to their eusocial organization as well as their ability to digest dead plant tissues. While being extremely abundant, the termite diet is poor in crucial nutrients, such as fatty acids. Linoleic acid (LA) is a precursor for many vital biomolecules, and most animals depend on its dietary supply. Termites count among the exceptions known to produce LA de novo, presumably via the action of an unknown Δ12 fatty acyl desaturase (FAD) introducing the second double bond into monounsaturated oleic acid. Here, we search for the evolutionary origin of LA biosynthesis in termites. To this end, we compile the repertoire of FAD homologs from 57 species of termites and their closest relatives, the cockroaches, analyze FAD phylogeny, and identify a potential Δ12 FAD branch, which arose through duplication of a likely Δ9 FAD. We functionally characterize both paralogs and identify the Δ9 activity in the ancestral FAD-A1a and the Δ12 activity responsible for LA biosynthesis in FAD-A1b. Through the combination of homology modeling and site-directed mutagenesis, we pinpoint structural features possibly contributing to the distinct functions, regiospecificities, and substrate preferences of the two enzymes. We confirm the presence of both paralogs in all 36 studied species of the Blattoidea lineage (Blattidae, Lamproblattidae, Cryptocercidae, and termites) and conclude that we identified an evolutionary event important for the ecological success of termites, which took place in their cockroach ancestors roughly 160 My and remained conserved throughout termite diversification into 3,000 extant species.

Understanding desaturation/hydroxylation activity of castor stearoyl Δ9-Desaturase through rational mutagenesis.

A recently proposed reaction mechanism of soluble Δ9 desaturase (Δ9D) allowed us to identify auxiliary residues His203, Asp101, Thr206 and Cys222 localized near the di-iron active site that are supposedly involved in the proton transfer (PT) to and from the active site. The PT, along with the electron transfer (ET), seems to be crucial for efficient desaturation. Thus, perturbing the major PT chains is expected to impair the native reaction and (potentially) amplify minor reaction channels, such as the substrate hydroxylation. To verify this hypothesis, we mutated the four residues mentioned above into their counterparts present in a soluble methane monooxygenase (sMMO), and determined the reaction products of mutants. We found that the mutations significantly promote residual monohydroxylation activities on stearoyl-CoA, often at the expense of native desaturation activity. The favored hydroxylation positions are C9, followed by C10 and C11. Reactions with unsaturated substrate, oleoyl-CoA, yield erythro-9,10-diol, cis-9,10-epoxide and a mixture of allylic alcohols. Additionally, using 9- and 11-hydroxystearoyl-CoA, we showed that the desaturation reaction can proceed only with the hydroxyl group at position C11, whereas the hydroxylation reaction is possible in both cases, i.e. with hydroxyl at position C9 or C11. Despite the fact that the overall outcome of hydroxylation is rather modest and that it is mostly the desaturation/hydroxylation ratio that is affected, our results broaden understanding of the origin of chemo- and stereoselectivity of the Δ9D and provide further insight into the catalytic action of the NHFe2 enzymes.

Crystal structure of carbonic anhydrase CaNce103p from the pathogenic yeast Candida albicans.

BACKGROUND: The pathogenic yeast Candida albicans can proliferate in environments with different carbon dioxide concentrations thanks to the carbonic anhydrase CaNce103p, which accelerates spontaneous conversion of carbon dioxide to bicarbonate and vice versa. Without functional CaNce103p, C. albicans cannot survive in atmospheric air. CaNce103p falls into the ß-carbonic anhydrase class, along with its ortholog ScNce103p from Saccharomyces cerevisiae. The crystal structure of CaNce103p is of interest because this enzyme is a potential target for surface disinfectants. RESULTS: Recombinant CaNce103p was prepared in E. coli, and its crystal structure was determined at 2.2 Å resolution. CaNce103p forms a homotetramer organized as a dimer of dimers, in which the dimerization and tetramerization surfaces are perpendicular. Although the physiological role of CaNce103p is similar to that of ScNce103p from baker's yeast, on the structural level it more closely resembles carbonic anhydrase from the saprophytic fungus Sordaria macrospora, which is also tetrameric. Dimerization is mediated by two helices in the N-terminal domain of the subunits. The N-terminus of CaNce103p is flexible, and crystals were obtained only upon truncation of the first 29 amino acids. Analysis of CaNce103p variants truncated by 29, 48 and 61 amino acids showed that residues 30-48 are essential for dimerization. Each subunit contains a zinc atom in the active site and displays features characteristic of type I ß-carbonic anhydrases. Zinc is tetrahedrally coordinated by one histidine residue, two cysteine residues and a molecule of ß-mercaptoethanol originating from the crystallization buffer. The active sites are accessible via substrate tunnels, which are slightly longer and narrower than those observed in other fungal carbonic anhydrases. CONCLUSIONS: CaNce103p is a ß-class homotetrameric metalloenzyme composed of two homodimers. Its structure closely resembles those of other ß-type carbonic anhydrases, in particular CAS1 from Sordaria macrospora. The main differences occur in the N-terminal part and the substrate tunnel. Detailed knowledge of the CaNce103p structure and the properties of the substrate tunnel in particular will facilitate design of selective inhibitors of this enzyme.

Glucosamine sulfate use and delay of progression of knee osteoarthritis: a 3-year, randomized, placebo-controlled, double-blind study.

BACKGROUND: Conventional symptomatic treatments for osteoarthritis do not favorably affect disease progression. The aim of this randomized, placebo-controlled trial was to determine whether long-term (3-year) treatment with glucosamine sulfate can modify the progression of joint structure and symptom changes in knee osteoarthritis, as previously suggested. METHODS: Two hundred two patients with knee osteoarthritis (using American College of Rheumatology criteria) were randomized to receive oral glucosamine sulfate, 1500 mg once a day, or placebo. Changes in radiographic minimum joint space width were measured in the medial compartment of the tibiofemoral joint, and symptoms were assessed using the algo-functional indexes of Lequesne and WOMAC (Western Ontario and McMaster Universities). RESULTS: Osteoarthritis was of mild to moderate severity at enrollment, with average joint space widths of slightly less than 4 mm and a Lequesne index score of less than 9 points. Progressive joint space narrowing with placebo use was -0.19 mm (95% confidence interval, -0.29 to -0.09 mm) after 3 years. Conversely, there was no average change with glucosamine sulfate use (0.04 mm; 95% confidence interval, -0.06 to 0.14 mm), with a significant difference between groups (P =.001). Fewer patients treated with glucosamine sulfate experienced predefined severe narrowings (>0.5 mm): 5% vs 14% (P =.05). Symptoms improved modestly with placebo use but as much as 20% to 25% with glucosamine sulfate use, with significant final differences on the Lequesne index and the WOMAC total index and pain, function, and stiffness subscales. Safety was good and without differences between groups. CONCLUSION: Long-term treatment with glucosamine sulfate retarded the progression of knee osteoarthritis, possibly determining disease modification.