• Biocatalysts from Biosynthetic Pathways: Enabling Stereoselective, Enzymatic Cycloether Formation on a Gram Scale

      Hollmann, Tim; Berkhan, Gesche; Wagner, Lisa; Sung, Kwang Hoon; Kolb, Simon; Geise, Hendrik; Hahn, Frank; HZI,Helmholtz-Zentrum für Infektionsforschung GmbH, Inhoffenstr. 7,38124 Braunschweig, Germany. (American Chemical Society (ACS), 2020-03-30)
      Biosynthetic pathways of natural products contain many enzymes that contribute to the rapid assembly of molecular complexity. Enzymes that form complex structural elements with multiple stereocenters, like chiral saturated oxygen heterocycles (CSOH), are of particular interest for a synthetic application, as their use promises to significantly simplify access to these elements. Here, the biocatalytic characterization of AmbDH3, an enzyme that catalyzes intramolecular oxa-Michael addition (IMOMA) is reported. This reaction essentially gives access to various types of CSOH with adjacent stereocenters, but it is not yet part of the repertoire of preparative biocatalysis. An in-depth study on the synthetic utility of AmbDH3 was performed, which made extensive use of complex synthetic precursor surrogates. The enzyme exhibited stability and broad substrate tolerance in in vitro experiments, which was in agreement with the results of molecular modeling. Its selectivity profile enabled kinetic resolution of chiral tetrahydropyrans (THPs) under control of up to four stereocenters. A systematic optimization of the reaction conditions enabled gram-scale conversions yielding preparative amounts of chiral THP. The synthetic utility of AmbDH3 was finally demonstrated by its successful application in the key step of a chemoenzymatic total synthesis to the THP-containing phenylheptanoid (−)-centrolobine. These results highlight the synthetic potential of AmbDH3 and related IMOMA cyclases as a biocatalytic alternative that further develops the available chemical-synthetic IMOMA methodology.
    • Structural insights into antigen recognition of an anti-β-(1,6)-β-(1,3)-D-glucan antibody.

      Sung, Kwang Hoon; Josewski, Jörn; Dübel, Stefan; Blankenfeldt, Wulf; Rau, Udo; HZI,Helmholtz-Zentrum für Infektionsforschung GmbH, Inhoffenstr. 7,38124 Braunschweig, Germany. (2018-09-12)
      Schizophyllan (SCH) is a high molecular weight homopolysaccharide composed of a β-(1,3)-D-glucan main chain with branching β-(1,6)-bound D-glucose residues. It forms triple helices that are highly stable towards heat and extreme pH, which provides SCH with interesting properties for industrial and medical applications. The recombinant anti-SCH antibody JoJ48C11 recognizes SCH and related β-(1,6)-branched β-(1,3)-D-glucans, but details governing its specificity are not known. Here, we fill this gap by determining crystal structures of the antigen binding fragment (Fab) of JoJ48C11 in the apo form and in complex with the unbranched β-(1,3)-D-glucose hexamer laminarihexaose 3.0 and 2.4 Å resolution, respectively. Together with docking studies, this allowed construction of a JoJ48C11/triple-helical SCH complex, leading to the identification of eight amino acid residues of JoJ48C11 (Tyr27