Biological sources, metabolism, and production of glucosylglycerols, a group of natural glucosides of biotechnological interest

Glucosylglycerols (GGs) are a group of functional heterosides comprising glycerol and glucose. In nature, they are mainly produced by many moderately salt-tolerant cyanobacteria as compatible solutes in a salt-dependent manner and synthesized in a few higher plants and fermentation processes. Because of their many interesting physicochemical properties and biological activities, such as low sweetness, low hygroscopicity, high water-holding capacity, excellent biocompatibility, favorable performance in protecting macromolecules, and antitumor activity, GGs exhibit large application potential in the fields of cosmetics, health care, food service, enzyme production, and pharmaceuticals. Many in vitro systems using different members of the GH (glycoside hydrolase) family have been established for the enzymatic synthesis of GGs, and a few of them are in use for commercial production. Based on a good understanding of the genetic bases, biochemical processes, and regulatory mechanisms of GG metabolism in microorganisms (mainly cyanobacteria), in recent years GG production technologies with in vivo systems have also been developed by applying metabolic and bioprocess engineering to a few native or heterologous microbial cell factories. This successfully provides the market GG products with an alternative source. With the further elucidation of details about the biological functions of GGs and related mechanisms, the application scope of GGs will be greatly expanded. In the present review, the biological sources and physiological roles of GGs, the molecular bases and regulation of GG metabolism, and the recent progress in GG production and application are systematically summarized. A few new questions that have arisen in the basic research of GGs and perspectives on GG application are also discussed.

Development of Hinoline® as a natural preservative for cosmetic product using bioinspiration and Greenpharma Database

AIMS

The cosmetic industry needs new preservatives that are effective, natural, safe, cost effective, sustainable and compliant with regulatory standards. This necessity has posed challenges requiring obligations, bioinformatics and bioinspiration as driving forces.

METHODS AND RESULTS

Twenty natural extracts were selected from the Greenpharma Database with parameter filters corresponding to development constraints and antimicrobial properties. We confirmed using minimum inhibition concentration (MIC) assays that eight of the extracts have good bactericidal properties and that one has a high antifungal activity. The latter was purified hinokitiol, a bioproduct from Aomori Hiba wood. This substance provides high resistance against putrefaction; for instance, old Japanese temples were made of Aomori Hiba wood. The combination of hinokitiol with levulinic acid, another bioproduct, demonstrated complementary antimicrobial activities and synergistic effects in MIC studies and measurements according to Kull synergy index. Further, the mixture Hinoline® was tested at 2% in challenge tests and fulfilled criteria A of different standards. It also exerted complementary preservative effects with potassium sorbate and beneficial effects in unbalanced skin microbiota.

CONCLUSION

Hinoline, a new effective preservative from renewable bioresources, was developed.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study accelerates the development of a preservative solution for cosmetics selected from Greenpharma Database, through bioinspiration and the identification of cost-effective investments and resources.

Crystal structure of Dictyoglomus thermophilum β-d-xylosidase DtXyl unravels the structural determinants for efficient notoginsenoside R1 hydrolysis

Dictyoglomus thermophilum β-d-xylosidase DtXyl is attractive as a potential thermostable biocatalyst able to produce biologically active ginsenosides intermediates from β-(1,2)-D-xylosylated compounds, including Notoginsenoside-R1. DtXyl was expressed as an active N-terminal His-tagged protein, and its crystal structure was solved in presence or absence of d-xylose product. Modelling of notoginsenoside R1 in DtXyl active site led to the identification of several hydrophobic residues interacting in close contact to the substrate hydrophobic core. Unlike other residues involved in substrate binding, these residues are not conserved among GH39 xylosidase family, and their physico-chemical properties can be correlated to the efficient binding and subsequent hydrolysis of Notoginsenoside R1.

Hydrolysis of Glycosyl Thioimidates by Glycoside Hydrolase Requires Remote Activation for Efficient Activity

Chemoenzymatic synthesis of glycosides relies on efficient glycosyl donor substrates able to react rapidly and efficiently, yet with increased stability towards chemical or enzymatic hydrolysis. In this context, glycosyl thioimidates have previously been used as efficient donors, in the case of hydrolysis or thioglycoligation. In both cases, the release of the thioimidoyl aglycone was remotely activated through a protonation driven by a carboxylic residue in the active site of the corresponding enzymes. A recombinant glucosidase (DtGly) from Dictyoglomus themophilum, previously used in biocatalysis, was also able to use such glycosyl thioimidates as substrates. Yet, enzymatic kinetic values analysis, coupled to mutagenesis and in silico modelling of DtGly/substrate complexes demonstrated that the release of the thioimidoyl moiety during catalysis is only driven by its leaving group ability, without the activation of a remote protonation. In the search of efficient glycosyl donors, glycosyl thioimidates are attractive and efficient. Their utility, however, is limited to enzymes able to promote leaving group release by remote activation.

Biochemical Characterization of the α-l-Rhamnosidase DtRha from Dictyoglomus thermophilum: Application to the Selective Derhamnosylation of Natural Flavonoids

α-l-Rhamnosidases are catalysts of industrial tremendous interest, but their uses are still somewhat limited by their poor thermal stabilities and selectivities. The thermophilic DtRha from Dictyoglomus thermophilum was cloned, and the recombinant protein was easily purified to homogeneity to afford 4.5 mg/L culture of biocatalyst. Michaelis-Menten parameters demonstrated it to be fully specific for α-l-rhamnose. Most significantly, DtRha demonstrated to have a stronger preference for α(1 → 2) linkage rather than α(1 → 6) linkage when removing rhamnosyl moiety from natural flavonoids. This selectivity was fully explained by the difference of binding of the corresponding substrates in the active site of the protein.