Organic Chemistry Seminar – Jacob Lewis, Chemistry Graduate Student

About the event

Speaker: Jacob Lewis, chemistry graduate student

Group: Chulhee Kang

Title: The Intersection of Biofuel and Crop Resilience: Enzymatic Characterization for Future Engineering

Abstract: Flavonoids are potent antioxidants, which play a role in defense against pathogens and insects, attracting pollinators, protection against UV-radiation and reactive oxygen species. Furthermore, flavonoids have been linked with a vast array of health benefits from disease treatments to food preservation. The flavonoid pathway diverts biomass from the lignin pathway making it ideal for engineering for ease of access to biofuel via cellulose. The divergent enzyme, chalcone synthase (CHS) is promiscuous in its specificity and product formation. However, the promiscuity can be rectified with chalcone isomerase (CHI) or chalcone isomerase like protein (CHIL). 3D structures of these three enzymes have been obtained elucidating the enzyme-enzyme interactions. Further downstream,  dihydroflavonol 4-reductase (DFR) and flavanone 4-reductase (FNR) catalyze the reduction of dihydroflavonols and flavanones using NAD(P)H to produce various flavon-(3)-4-(di)ols in the central steps of flavonoid synthesis. Anthocyanidin reductase (ANR) catalyzes the reduction of anthocyanidins to flavan-3-ols. In addition to their amino acid sequence similarity, the 3D structures of recombinant DFR, FNR and ANR from sorghum and switchgrass showed similarities, including a continuous NADPH-binding Rossman-fold domain and substrate-binding motif.  The catalytic mechanism and substrate specificity of the reductases were deduced from crystal structures, site-directed mutagenesis, and kinetic and thermodynamic analyses.  Although DFR displayed higher activity against dihydroflavonols, it also showed significant activity against flavanones and anthocyanidins, and was inhibited by the flavonol quercetin. SbFNR1 and SbFNR2 did not show any activity against dihydroflavonols, but SbFNR1 displayed significant activity against flavanones. SbFNR1 and SbFNR2 also displayed significant ANR activity against two anthocyanidins, cyanindin and pelagornidin, reducing them to the corresponding flavan-3-ols.