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Microbiology 155 (2009), 1858-1865; DOI  10.1099/mic.0.026609-0
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Microbiology 155 (2009), 1858-1865; DOI  10.1099/mic.0.026609-0
© 2009 Society for General Microbiology

Homocysteine editing and growth inhibition in Escherichia coli

Marta Sikora1,2 and Hieronim Jakubowski1,2

1 Department of Microbiology and Molecular Genetics, UMDNJ-New Jersey Medical School, International Center for Public Health, Newark, NJ 07101, USA
2 Institute of Bioorganic Chemistry, Polish Academy of Sciences, Poznan, Poland

In Escherichia coli homocysteine (Hcy) is metabolically converted to the thioester Hcy-thiolactone in ATP-consuming reactions catalysed 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 mole of ATP unproductively dissipated for Hcy-thiolactone synthesis per each mole 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.

Correspondence
Hieronim Jakubowski
jakubows{at}umdnj.edu

Abbreviations: DTT, dithiothreitol; Hcy, homocysteine; MetRS, methionyl-tRNA synthetase; IleRS, isoleucyl-tRNA synthetase; LeuRS, leucyl-tRNA synthetase






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