Novel tools for the study of class I alpha-mannosidases: a chromogenic substrate and a substrate-analog inhibitor

Characterization of Solitalea canadensis α-mannosidase with specific activity towards α1,3-Mannosidic linkages

A recombinant exo-α-mannosidase from Solitalea canadensis (Sc3Man) has been characterized to exhibit strict specificity for hydrolyzing α1,3-mannosidic linkages located at the non-reducing end of glycans containing α-mannose. Enzymatic characterization revealed that Sc3Man operates optimally at a pH of 5.0 and at a temperature of 37 °C. The enzymatic activity was notably enhanced twofold in the presence of Ca2+ ions, emphasizing its potential dependency on this metal ion, while Cu2+ and Zn2+ ions notably impaired enzyme function. Sc3Man was able to efficiently cleave the terminal α1,3 mannose residue from various high-mannose N-glycan structures and from the model glycoprotein RNase B. This work not only expands the categorical scope of bacterial α-mannosidases, but also offers new insight into the glycan metabolism of S. canadensis, highlighting the enzyme's utility for glycan analysis and potential biotechnological applications.

Tandem Allylboration-Prins Reaction for the Rapid Construction of Substituted Tetrahydropyrans: Application to the Total Synthesis of (-)-Clavosolide A

Tetrahydropyrans are common motifs in natural products and have now been constructed with high stereocontrol through a three‐component allylboration‐Prins reaction sequence. This methodology has been applied to a concise (13 steps) and efficient (14 % overall yield) synthesis of the macrolide (−)‐clavosolide A. The synthesis also features an early stage glycosidation reaction to introduce the xylose moiety and a lithiation‐borylation reaction to attach the cyclopropyl‐containing side chain.

Synthesis of the Mixed Acetal Segment of S-Glyceroplasmalopsychosine

In this report the concept of converting carbohydrate to non-carbohydrate asymmetric molecules has been successfully exploited. The mixed acetal segment of glyceroplasmalopsychosine, a novel glycolipid has been synthesized in a stereo-specific manner using two simple sugar units. The glycosidation reaction between these two monosaccharides ensured the correct acetal stereocenter of the target molecule. Either olefin metathesis or heterogeneous Wittig reactions were used for constructing the long aliphatic chain of glyceroplasmalopsychosine.

Modulation of activity by Arg407: structure of a fungal alpha-1,2-mannosidase in complex with a substrate analogue

Class I alpha-mannosidases (glycoside hydrolase family GH47) play key roles in the maturation of N-glycans and the ER-associated degradation of unfolded glycoproteins. The 1.95 A resolution structure of a fungal alpha-1,2-mannosidase in complex with the substrate analogue methyl-alpha-D-lyxopyranosyl-(1',2)-alpha-D-mannopyranoside (LM) shows the intact disaccharide spanning the -1/+1 subsites, with the D-lyxoside ring in the -1 subsite in the 1C4 chair conformation, and provides insight into the mechanism of catalysis. The absence of the C5' hydroxymethyl group on the D-lyxoside moiety results in the side chain of Arg407 adopting two alternative conformations: the minor one interacting with Asp375 and the major one interacting with both the D-lyxoside and the catalytic base Glu409, thus disrupting its function. Chemical modification of Asp375 has previously been shown to inactivate the enzyme. Taken together, the data suggest that Arg407, which belongs to the conserved sequence motif RPExxE, may act to modulate the activity of the enzyme. The proposed mechanism for modulating the activity is potentially a general mechanism for this superfamily.

A hydrophobic platform as a mechanistically relevant transition state stabilising factor appears to be present in the active centre of all glycoside hydrolases

An in silico survey of the -1 subsite of all known 3D-structures of O-glycoside hydrolases containing a suitably positioned ligand has led to the recognition -- apparently without exceptions -- of a transition state stabilising hydrophobic platform which is complementary to a crucial hydrophobic patch of the ligand. This platform is family-specific and highly conserved. A comprehensive list is given with examples of enzymes belonging to 33 different families. Several typical constellations of platform - protein residues are described.