The Geobacillus stearothermophilus V cobA gene encoding uroporphyrinogen-III C-methyltransferase (also referred to as SUMT) was cloned into Escherichia coli and the recombinant enzyme was overexpressed and purified to homogeneity. The enzyme binds S-adenosyl-l-methionine and catalyzes the production of III methyl uroporphyrinogen in vitro. E. coli cells expressing the G. stearothermophilus V cobA gene exhibited increased resistance to potassium tellurite and potassium tellurate. Site-directed mutagenesis of cobA abolished tellurite resistance of the mesophilic, heterologous host and SUMT activity in vitro. No methylated, volatile derivatives of tellurium were found in the headspace of tellurite-exposed cobA-expressing E. coli, suggesting that the role of SUMT methyltransferase in tellurite(ate) detoxification is not related to tellurium volatilization.
Bibliographical noteFunding Information:
This work received financial support from Fondecyt grant # 1060022 and Dicyt-USACH to C.C.V. and from the Robert A. Welch Foundation (X-011) at Sam Houston State University to T.G.C. and R.B.
M.A.A. and D.E.F. were supported by doctoral fellowships from Mecesup, Chile. I.L.C. received a doctoral fellowship from Conicyt, Chile and J.M.P. was supported by Mecesup, Conicyt and Dicyt-USACH, Chile.