Effects of a proteasome inhibitor on the riboflavin production in Ashbya gossypii.

Abstract

Effects of a proteasome inhibitor, MG-132, on the riboflavin production in Ashbya gossypii were investigated to elucidate the relationship of the riboflavin production with flavoprotein homeostasis. The addition of MG-132 to the liquid medium reduced the specific riboflavin production by 79% in A. gossypii at 25μM after 24h. The addition of the inhibitor also caused the accumulation of reactive oxygen species and ubiquitinated proteins. These results indicated that MG-132 works in A. gossypii without any genetic engineering and reduces riboflavin production. In the presence of 25μM MG-132, specific NADH dehydrogenase activity was increased by 1.4-fold compared to DMSO, but specific succinate dehydrogenase (SDH) activity was decreased to 52% compared to DMSO. Additionally, the amount of AgSdh1p (ACR052Wp) was also reduced. Specific riboflavin production was reduced to 22% when 20mM malonate, a SDH inhibitor, was added to the culture medium. The riboflavin production in heterozygous AgSDH1gene-disrupted mutant (AgSDH1-/+ ) was reduced to 63% compared to that in wild type. MG-132 suppresses the riboflavin production and SDH activity in A. gossypii. SDH is one of the flavoproteins involved in the riboflavin production in A. gossypii. This study shows that MG-132 has a negative influence on the riboflavin production and SDH activity in A. gossypii and leads to the elucidation of the connection of the riboflavin production with flavoproteins.