Involvement of a flavoprotein, acetohydroxyacid synthase, in growth and riboflavin production in riboflavin-overproducing Ashbya gossypii mutant

by Selleckchem | Aug 16 2023

Background: Previously, we isolated a riboflavin-overproducing Ashbya gossypii mutant (MT strain) and discovered some mutations in genes encoding flavoproteins. Here, we analyzed the riboflavin production in the MT strain, in view of flavoproteins, which are localized in the mitochondria.

Results: In the MT strain, mitochondrial membrane potential was decreased compared with that in the wild type (WT) strain, resulting in increased reactive oxygen species. Additionally, diphenyleneiodonium (DPI), a universal flavoprotein inhibitor, inhibited riboflavin production in the WT and MT strains at 50 µM, indicating that some flavoproteins may be involved in riboflavin production. The specific activities of NADH and succinate dehydrogenases were significantly reduced in the MT strain, but those of glutathione reductase and acetohydroxyacid synthase were increased by 4.9- and 25-fold, respectively. By contrast, the expression of AgGLR1 gene encoding glutathione reductase was increased by 32-fold in the MT strain. However, that of AgILV2 gene encoding the catalytic subunit of acetohydroxyacid synthase was increased by only 2.1-fold. These results suggest that in the MT strain, acetohydroxyacid synthase, which catalyzes the first reaction of branched-chain amino acid biosynthesis, is vital for riboflavin production. The addition of valine, which is a feedback inhibitor of acetohydroxyacid synthase, to a minimal medium inhibited the growth of the MT strain and its riboflavin production. In addition, the addition of branched-chain amino acids enhanced the growth and riboflavin production in the MT strain.

Conclusion: The significance of branched-chain amino acids for riboflavin production in A. gossypii is reported and this study opens a novel approach for the effective production of riboflavin in A. gossypii.

Comments:

The study you mentioned focused on riboflavin production in an Ashbya gossypii mutant strain (MT strain) compared to the wild type (WT) strain. The researchers found that the MT strain exhibited decreased mitochondrial membrane potential, leading to an increase in reactive oxygen species (ROS). They also observed that diphenyleneiodonium (DPI), a flavoprotein inhibitor, inhibited riboflavin production in both the WT and MT strains at a concentration of 50 µM, suggesting the involvement of flavoproteins in riboflavin production.

Further analysis revealed that the specific activities of NADH and succinate dehydrogenases, two flavoproteins, were significantly reduced in the MT strain. On the other hand, the specific activities of glutathione reductase and acetohydroxyacid synthase were increased by 4.9- and 25-fold, respectively. Interestingly, the expression of the AgGLR1 gene, which encodes glutathione reductase, was increased by 32-fold in the MT strain. However, the expression of the AgILV2 gene, encoding the catalytic subunit of acetohydroxyacid synthase, was only increased by 2.1-fold.

Based on these findings, the researchers proposed that acetohydroxyacid synthase, an enzyme involved in the first step of branched-chain amino acid biosynthesis, plays a vital role in riboflavin production in the MT strain. The addition of valine, a feedback inhibitor of acetohydroxyacid synthase, to a minimal medium inhibited the growth of the MT strain and its riboflavin production. Conversely, the addition of branched-chain amino acids enhanced the growth and riboflavin production in the MT strain.

In conclusion, this study highlights the significance of branched-chain amino acids for riboflavin production in A. gossypii. The findings provide insights into the role of flavoproteins, particularly acetohydroxyacid synthase, in regulating riboflavin production in this mutant strain. This research opens up new possibilities for improving the effective production of riboflavin in A. gossypii.