Insect midgut α-mannosidases from family 38 and 47 with emphasis on those of Tenebrio molitor

Enantiomeric C-6 fluorinated swainsonine derivatives as highly selective and potent inhibitors of α-mannosidase and α-l-rhamnosidase: Design, synthesis and structure-activity relationship study

Six C-6 fluorinated d-swainsonine derivatives and their enantiomers have been designed based on initial docking calculations, and synthesized from enantiomeric ribose-derived aldehydes, respectively. Glycosidase inhibition assay of these derivatives with d-swainsonine (1) and l-swainsonine (ent-1) as contrasts found that the C-6 fluorinated d-swainsonine derivatives with C-8 configurations as R (α) showed specific and potent inhibitions of jack bean α-mannosidase (model enzyme of Golgi α-mannosidase II); whereas their enantiomers with C-8 configurations as S (β) were powerful and selective α-l-rhamnosidase inhibitors. Molecular docking calculations found the C-6 fluorinatedd-swainsonine derivatives 21, 24 and 25 with highly coincident binding conformations with d-swainsonine (1) in their interactions with the active site of α-mannosidase (PDB ID: 1HWW). Reliability of the docking results were confirmed by Molecular Dynamics (MD) simulation. Additionally, solid interactions with residues Gln-392 and Tyr-393 in the active site of α-l-rhamnosidase (PDB ID: 3W5N) were proved to be vital for potent α-l-rhamnosidase inhibitions of the l-swainsonine derivatives. The role of C-6 fluorines in swainsonine derivatives well demonstrated the "mimic effect" of fluorine to hydrogen by minimal influence on the binding conformations and effective compensation for any possible lost interactions. This work contributes to a comprehensive understanding of the structure-activity relationship (SAR) of the fluorinated swainsonines and ever reported branched swainsonines, and has laid good foundation for development of more potent α-mannosidase and α-l-rhamnosidase inhibitors.

Expression and Characterization of a GH38 α-Mannosidase from the Hyperthermophile Pseudothermotoga thermarum

This study focused on the bio-characterization of a GH38 α-mannosidase from the hyperthermophile Pseudothermotoga thermarum DSM 5069. We aimed to successfully express and characterize this thermophilic α-mannosidase and to assess its functional properties. Subsequently, recombinant α-mannosidase PtαMan was expressed in Escherichia coli BL21(DE3) and purified via affinity chromatography, and native protein was verified as a tetramer by size exclusion chromatography. In addition, the activity of α-mannosidase PtαMan was relatively stable at pH 5.0-6.5 and temperatures up to 75 ℃. α-Mannosidase PtαMan was active toward Co²⁺ and had a good catalytic efficiency deduced from the kinetic parameters. However, its activity was strongly inhibited by Cu²⁺, Zn²⁺, SDS, and swainsonine. In summary, this cobalt-required α-mannosidase is putatively involved in the direct modification of glycoproteins.

Fates of dietary sterols in the insect alimentary canal

Sterols serve structural and physiological roles in insects. However, insects and other arthropods have lost many genes in the sterol biosynthesis pathway, so they must acquire sterols from their food. Sterols occur naturally as free (unconjugated) molecules, and as conjugated ones (mostly steryl esters). Once sterols are ingested and make their way into the gut, steryl esters can be converted into free sterols by Magro protein, a lipase excreted by enterocytes. Sterols in the free form enter midgut enterocytes through NPC1b and are then transported to the smooth endoplasmic reticulum membrane for possible metabolism. For most insect herbivores, phytosterol dealkylation converts plant sterols into cholesterol. Some ingested sterols may also be consumed by microbiota dwelling inside the insect gut lumen; bacteria use sterols as a source of carbon and energy. Further studies will reveal interesting and exciting discoveries regarding the pathways for the dietary sterols entering the insect alimentary canal.

Standardization of a Continuous Assay for Glycosidases and Its Use for Screening Insect Gut Samples at Individual and Populational Levels

Glycoside Hydrolases (GHs) are enzymes able to recognize and cleave glycosidic bonds. Insect GHs play decisive roles in digestion, in plant-herbivore, and host-pathogen interactions. GH activity is normally measured by the detection of a release from the substrate of products as sugars units, colored, or fluorescent groups. In most cases, the conditions for product release and detection differ, resulting in discontinuous assays. The current protocols result in using large amounts of reaction mixtures for the obtainment of time points in each experimental replica. These procedures restrain the analysis of biological materials with limited amounts of protein and, in the case of studies regarding small insects, implies in the pooling of samples from several individuals. In this respect, most studies do not assess the variability of GH activities across the population of individuals from the same species. The aim of this work is to approach this technical problem and have a deeper understanding of the variation of GH activities in insect populations, using as models the disease vectors Rhodnius prolixus (Hemiptera: Triatominae) and Lutzomyia longipalpis (Diptera: Phlebotominae). Here we standardized continuous assays using 4-methylumbelliferyl derived substrates for the detection of α-Glucosidase, β-Glucosidase, α-Mannosidase, N-acetyl-hexosaminidase, β-Galactosidase, and α-Fucosidase in the midgut of R. prolixus and L. longipalpis with results similar to the traditional discontinuous protocol. The continuous assays allowed us to measure GH activities using minimal sample amounts with a higher number of measurements, resulting in data that are more reliable and less time and reagent consumption. The continuous assay also allows the high-throughput screening of GH activities in small insect samples, which would be not applicable to the previous discontinuous protocol. We applied continuous GH measurements to 90 individual samples of R. prolixus anterior midgut homogenates using a high-throughput protocol. α-Glucosidase and α-Mannosidase activities showed the normal distribution in the population. β-Glucosidase, β-Galactosidase, N-acetyl-hexosaminidase, and α-Fucosidase activities showed non-normal distributions. These results indicate that GHs fluorescent-based high-throughput assays apply to insect samples and that the frequency distribution of digestive activities should be considered in data analysis, especially if a small number of samples is used.