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Homocysteine editing and growth inhibition in Escherichia coli

¹ Institute of Biorganic Chemistry, Poznan;
² UMDNJ-New Jersey Medical School

ABSTRACT

In Escherichia coli homocysteine (Hcy) is metabolically converted to the thioester Hcy-thiolactone in ATP-consuming reactions catalyzed by methionyl-, isoleucyl-, and leucyl-tRNA synthetases. Here we show that growth inhibition caused by supplementation of E. coli cultures with Hcy is accompanied by greatly increased accumulation of Hcy-thiolactone. Energy dissipation for Hcy editing increases 100-fold in the presence of exogenous Hcy and reaches one mol ATP unproductively dissipated for Hcy-thiolactone synthesis per each mol of ATP that is consumed for methionine activation. Inhibiting Hcy-thiolactone synthesis with isoleucine, leucine, or methionine accelerates bacterial growth in Hcy-supplemented cultures. Growth rates in Hcy-inhibited cultures are inversely related to the accumulation of Hcy-thiolactone. We also show that the levels of protein N-linked Hcy modestly increase in E. coli cells in Hcy-supplemented cultures. The results suggest that Hcy editing restrains bacterial growth.

³ E-mail: jakubows{at}umdnj.edu