Nickel is required by many microorganisms as a metalloenzyme cofactor (1,2). However, as with many inorganic nutrients, nickel is toxic so the amount and distribution of intracellular nickel is tightly controlled. One key mechanism of maintaining nickel homeostasis is through the activity of metalloregulators such as the nickel-dependent transcription factor NikR (3). This protein binds to specific DNA sequences upon activation by nickel and controls the expression of a variety of proteins involved in nickel homeostasis. Our work on the NikR homolog from Eschericia coli examines the mechanism of activation of DNA binding by nickel, and the metal selectivity of this process.Several types of physiologically-relevant transition metal ions bind to NikR, but nickel has a unique impact on the stability and structure of the protein, and activates the tightest complex with DNA. Biochemical analysis suggests that nickel selectively activates DNA binding by organizing secondary structural elements in the metal-binding domain of the protein, which stabilizes electrostatic contacts with the phosphodiester backbone of the DNA. The analysis of NikR mutants in E. coli demonstrates that these non-specific interactions are critical to the activity of NikR. Furthermore, cation exchange experiments and mutagenesis reveal that potassium is also necessary for the nickel-dependent response of NikR. These experiments support a multi-state mechanism of metal activation of E. coli NikR in which nickel operates through a selective allosteric impact on the protein structure (4.5).(1) Ragsdale (2009) JBC 284, 18571.(2) Li & Zamble (2009) Chem. Rev. 109, 681. (3) Iwig & Chivers (2010) Nat. Prod. Rep. 27, 658. (4) Wang, Dias, & Zamble (2009) Dalton Trans., 2459. (5) Phillips, Stultz, & Drennan (2010) Biochemistry 49, 7757.

Metal-selective activation of the nickel-responsive transcription factor NikR

247th National Meeting (2014)

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