Uncovering the role of branched-chain amino acid transaminases in Saccharomyces cerevisiae isobutanol biosynthesis.

TitleUncovering the role of branched-chain amino acid transaminases in Saccharomyces cerevisiae isobutanol biosynthesis.
Publication TypeJournal Article
Year of Publication2017
AuthorsHammer, SK, Avalos, JL
JournalMetab Eng
Volume44
Pagination302-312
Date Published2017 Nov
ISSN1096-7184
Abstract

Isobutanol and other branched-chain higher alcohols (BCHAs) are promising advanced biofuels derived from the degradation of branched-chain amino acids (BCAAs). The yeast Saccharomyces cerevisiae is a particularly attractive host for the production of BCHAs due to its high tolerance to alcohols and prevalent use in the bioethanol industry. Degradation of BCAAs begins with transamination reactions, catalyzed by branched-chain amino acid transaminases (BCATs) located in the mitochondria (Bat1p) and cytosol (Bat2p). However, the roles that these transaminases play in isobutanol production remain poorly understood and obscured by conflicting reports in the literature. In this work, we elucidate the influence of BCATs on isobutanol production in two genetic backgrounds (CEN.PK2-1C and BY4741). In the process, we uncover and characterize two competing isobutanol pathways, which can be manipulated by overexpressing or deleting BAT1 or BAT2, and adding or removing valine from the fermentation media. We show that deletion of BAT1 alone increases isobutanol production by 14.2-fold over wild type strains in media lacking valine, and examine how interactions between valine and the regulatory protein Ilv6p affect isobutanol production. Compartmentalizing the five-gene isobutanol biosynthetic pathway in mitochondria of BAT1 deletion strains results in an additional 2.1-fold increase in isobutanol production in the absence of valine. While valine inhibits isobutanol production, it boosts 2-methyl-1-butanol production. This work clarifies the role of transamination activity in BCHA biosynthesis, and develops valuable strategies and strains for future optimization of isobutanol production.

DOI10.1016/j.ymben.2017.10.001
Alternate JournalMetab. Eng.
PubMed ID29037781