Desmodium incanum subsp. soluble
Creators: name: Hao, B.
name: Caulfield, J. C.
name: Hamilton, M. L.
name: Pickett, J. A.
name: Midega, C. A. O.
name: Khan, Z. R.
name: Wang, J.
name: Hooper, A. M.
Publisher: name: Zenodo
Year: 2016
Subjects: Biodiversity
Taxonomy
Plantae
Tracheophyta
Magnoliopsida
Fabales
Fabaceae
Desmodium
Desmodium incanum

description: 2.5. Synthesis of 6- and 8-C-glucosylflavones from synthetic 2-
hydroxyflavanones by D. incanum soluble root proteins
In our previous work demonstrating the biosynthesis of allelopathic C -glycosylflavonoids found in the root exudates of Desmodium spp., we demonstrated C -glucosylation in this genus requires a 2-hydroxyflavonone substrate (Hamilton et al., 2009). We therefore challenged the soluble root proteins of D. incanum with the synthetic 2-hydroxyflavanones to assess whether there are significant differences in the capacity of D. incanum to C -glucosylate 2-hydroxyflavanones compared to the rice recombinant OsCGT protein (Table 3). Where standards were not available from the experiments with OsCGT which allowed NMR characterisation, the two products were analysed by high cone voltage ESIMS experiments to verify the C -glucosyl link to the flavonoid core through the loss of 90 and 120 amus (Fig. 1) (Cuyckens and Claeys, 2004) (Supplementary data). An example of the mass spectrometric analysis is shown for incubation assays with 3h (3 0,4 0 -methylenedioxy) (Fig. 2) and in this case the products are fully characterised as 5h and 6h. The differences between the two systems are small but relevant. OsCGT cannot C -glucosylate the sterically bulky 3n (t -butyl) and 3q (phenyl) while D. incanum can, implying a relaxed steric constraint. However, this is minimal as 3p (hexamethylenoxyl) still cannot be C -glycosylated by D. incanum as is the case with OsCGT. Minor differences include the acceptance by OsCGT of a brominated substrate 3v although at a very low level and 3i (3 0,5 0 -hydroxy) which was surprisingly not C -glycosylated by D. incanum proteins. A significant difference was the ability of D. incanum proteins to turn over chlorinated substrates which would allow the potential for generating chlorinated biologically active synthons for cross-coupling. These results demonstrate that crude D. incanum soluble protein has a different, though very similar capacity to accept novel substrates. These differences may be due to a single protein having a less sterically hindered substrate specificity for the substrate B-ring (3n and 3q) along with some different electronic requirements (3i, 3v, 3w, and 3x) or it may be due to different C -glycosyltransferases with a combined greater range of acceptable chemical space for 2-hydroxyflavanones. In any case, the plant has a greater capacity for producing novel C -glucoslyflavones than those possible using the single rice recombinant OsCGT.
description: Published as part of Hao, B., Caulfield, J. C., Hamilton, M. L., Pickett, J. A., Midega, C. A. O., Khan, Z. R., Wang, J. & Hooper, A. M., 2016, Biosynthesis of natural and novel C-glycosylflavones utilising recombinant Oryza sativa C-glycosyltransferase (OsCGT) and Desmodium incanum root proteins, pp. 73-87 in Phytochemistry 125 on page 76, DOI: 10.1016/j.phytochem.2016.02.013, http://zenodo.org/record/10485001