Characterization of The Cholesterol Biosynthetic Pathway In Dioscorea Transversa

Authors

Lauren J Salisbury
Stephen J Fletcher
Jeanette E Stok
Luke R Churchman
Joanne T Blanchfield
James J De Voss

Publication Date

6-1-2023

Journal

Journal of Biological Chemistry

Abstract

Cholesterol is the precursor of bioactive plant metabolites such as steroidal saponins. An Australian plant, Dioscorea transversa, produces only two steroidal saponins: 1β-hydroxyprotoneogracillin and protoneogracillin. Here, we used D. transversa as a model in which to elucidate the biosynthetic pathway to cholesterol, a precursor to these compounds. Preliminary transcriptomes of D. transversa rhizome and leaves were constructed, annotated, and analyzed. We identified a novel sterol side-chain reductase as a key initiator of cholesterol biosynthesis in this plant. By complementation in yeast, we determine that this sterol side-chain reductase reduces Δ^24,28 double bonds required for phytosterol biogenesis as well as Δ^24,25 double bonds. The latter function is believed to initiate cholesterogenesis by reducing cycloartenol to cycloartanol. Through heterologous expression, purification, and enzymatic reconstitution, we also demonstrate that the D. transversa sterol demethylase (CYP51) effectively demethylates obtusifoliol, an intermediate of phytosterol biosynthesis and 4-desmethyl-24,25-dihydrolanosterol, a postulated downstream intermediate of cholesterol biosynthesis. In summary, we investigated specific steps of the cholesterol biosynthetic pathway, providing further insight into the downstream production of bioactive steroidal saponin metabolites.

Keywords

cholesterol biosynthesis, CYP51, phytosterol biosynthesis, saponin, transcriptome

DOI

10.1016/j.jbc.2023.104768

PMID

37142228

PMCID

PMC10267570

PubMedCentral® Posted Date

May 2023

PubMedCentral® Full Text Version

Post-print

Published Open-Access

yes