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Effects of calcium on phosphatidylserine- and saposin C-stimulated glucosylceramide beta-glucosidase activity.

ABSTRACT: Glucosylceramide beta-glucosidase is a membrane-bound lysosomal hydrolase that is activated by acidic lipids, the most effective of which is phosphatidylserine (PtdSer), and an activator protein, saposin C. This report documents effects of Ca2+ ions on PtdSer- and saposin C-enhanced beta-glucosidase activity. Ca2+ either increased or decreased enzyme activity, depending on (1) the concentration of phospholipid, and (2) the presence or absence of saposin C. At PtdSer concentrations between 7.6 and 76 microM, in the absence of saposin C, Ca2+ caused an increase in beta-glucosidase activity up to 3 times that measured with PtdSer alone; this was due to both an increase in Vmax, and a decrease in Km. In contrast, at PtdSer concentrations greater than 100 microM, Ca2+ inhibited beta-glucosidase activity by 50%, due to a 2-fold increase in Km. Ca2+ was inhibitory at all PtdSer concentrations tested when both PtdSer and saposin C were present in the assay. Ca2+ ions were also shown to cause changes in the aggregation states of PtdSer. These results suggest that changes in Ca2+ concentration may play a role in regulating beta-glucosidase activity in vivo, thereby modulating sphingolipid metabolism. The implications of these findings are discussed.

SUBMITTER: Prence EM

PROVIDER: S-EPMC1135933 | biostudies-other | 1995 Sep

REPOSITORIES: biostudies-other

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Project description:Beta-glucosidases are key enzymes involved in lignocellulosic biomass degradation for bioethanol production, which complete the final step during cellulose hydrolysis by converting cellobiose into glucose. Currently, industry requires enzymes with improved catalytic performance or tolerance to process-specific parameters. In this sense, metagenomics has become a powerful tool for accessing and exploring the biochemical biodiversity present in different natural environments. Here, we report the identification of a novel β-glucosidase from metagenomic DNA isolated from soil samples enriched with decaying plant matter from a Secondary Atlantic Forest region. For this, we employed a functional screening approach using an optimized and synthetic broad host-range vector for library production. The novel β-glucosidase - named Lfa2 - displays three GH3-family conserved domains and conserved catalytic amino acids D283 and E487. The purified enzyme was most active in pH 5.5 and at 50°C, and showed hydrolytic activity toward several pNP synthetic substrates containing β-glucose, β-galactose, β-xylose, β-fucose, and α-arabinopyranose, as well as toward cellobiose. Lfa2 showed considerable glucose tolerance, exhibiting an IC50 of 300 mM glucose and 30% of remaining activity in 600 mM glucose. In addition, Lfa2 retained full or slightly enhanced activity in the presence of several metal ions. Further, β-glucosidase activity was increased by 1.7-fold in the presence of 10% (v/v) ethanol, a concentration that can be reached in conventional fermentation processes. Similarly, Lfa2 showed 1.7-fold enhanced activity at high concentrations of 5-hydroxymethyl furfural, one of the most important cellulase inhibitors in pretreated sugarcane bagasse hydrolysates. Moreover, the synergistic effect of Lfa2 on Bacillus subtilis GH5-CBM3 endoglucanase activity was demonstrated by the increased production of glucose (1.6-fold). Together, these results indicate that β-glucosidase Lfa2 is a promissory enzyme candidate for utilization in diverse industrial applications, such as cellulosic biomass degradation or flavor enhancement in winemaking and grape processing.

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Effects of calcium on phosphatidylserine- and saposin C-stimulated glucosylceramide beta-glucosidase activity.

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