348회 METHYLGLYOXAL and CELL GROWTH

348회

연사 :  박 찬 규, 한국과학기술원 생물과학과

제목: METHYLGLYOXAL and CELL GROWTH

Abstract

Methylglyoxal (MG) is a highly reactive metabolic intermediate, presumably accumulated by a physiological burden towards a phosphorylated sugar compound. The omnipresence of MG in diverse cell types led to an ancient hypothesis of its role as a growth regulator. The major source of MG is from dihydroxyacetone phosphate (DHAP), which is mediated by methylglyoxal synthase (mgs). The MG is further detoxified into D-lactate by a glutathione-dependent pathway.

We observed an E. coli cell death when the ribose transport system, consisting of the RbsDACBK proteins, was overproduced on multi-copy plasmids. An almost 100% of cell death occurs after a few hours of ribose addtion (>10 mM), due to an accumulation of extracellular methylglyoxal as detected by 3H-NMR. The lethal concentration of MG in the medium was more than 1 mM, which was measured by a spectroscopic method using 2,4-dinitrophenyl hydrazine. A deletion of RbsD, perhaps involved in ribose metabolism with unknown biochemical function, drastically lower the MG production below the lethal threshold, while an ablation of ribokinase (RbsK) completely abolished its production. This suggests that both an enhanced uptake and phosphorylation of ribose are required for the downstream metabolic partition into MG, in which the RbsD protein plays a critical role. A mutation in methylglyoxal synthase gene eliminates most of the MG in the medium but not completely abolishes its production, suggesting an alternative route to generate MG in the cell. Cells survived from ribose toxicity acquired a mutation either in the transport machinery (RbsABC) with lowered uptake efficiency or in the RbsD with a null function.