Properties of the Sp1 Zinc Finger 3 Peptide: Coordination Chemistry, Redox Reactions, and Metal Binding Competition with Metallothionein

Abstract

Toxic and/or carcinogenic consequences may result from metal ion substitution for the Zn-(II) in transcription factors containing zinc fingers, and the small Cys-rich metal-binding protein metallothionein (MT) may play a role in this metal substitution. To begin to evaluate this hypothesis, with regard to the carcinogenic metal ion Ni(II), a peptide corresponding to the third finger of the transcription factor Sp1 (Sp1-3) has been synthesized and its metal binding and redox reactions have been studied. The peptide binds Zn(II), Co(II), and Ni(II), with spectroscopic data indicating a tetrahedral coordination for the latter two; metal ion affinities have been quantified (Kd = 6 (+/- 3) x 10(-10), 3 (+/- 1) x 10(-7), and 4 (+/- 1) x 10(-6), respectively) and found to be less than those of an optimized zinc finger peptide (Krizek, B. A., Merkle, D. L., and Berg, J. M. (1993) Inorg. Chem. 32, 937-940) but greater than those of the second finger of transcription factor IIIA (Berg, J. M., and Merkle, D. L. (1989) J. Am. Chem. Soc. 111, 3759-3761). Reactions of the peptide and its metal-bound forms with dioxygen or hydrogen peroxide did not produce oxygen radical species; however, oxidation of the two Sp1-3 cysteines was modulated by metal ions (Zn < Co = apo < Ni), suggesting a protective role for Zn(II) but an enhancing role for Ni(II). Metal binding competition between Sp1-3 and the alpha domain of human liver MT-2 (alpha-hMT2) indicates a similar affinity for Zn(II). However, alpha-hMT2 has a higher affinity for Ni(II), suggesting that MT may play a protective role by ensuring Zn(II), rather than Ni(II), coordination to zinc finger sequences of transcription factors.

Reversible zinc exchange between metallothionein and the estrogen receptor zinc finger

“…Another study indicated that MT is capable of restoring DNA binding of ER in metalhuman aMT has a higher affinity for nickel than zinc, possidepleted extracts. This effect is similar to that of addition of bly preventing nickel-induced toxicity [15]. In our study, we non-protein bound zinc in the form of zinc acetate.…”

“…Nonetheless, the observed reversibility of zinc ex-~7 change in this study suggests that ER zinc fingers have an affinity for zinc similar to that of MT. While a recent study demonstrated metal exchange between a single synthetic Spl zinc finger peptide and the alpha domain of human MT [15], a contrasting report, [8] The reversible zinc exchange we report here indicates that lowing additions: (lanes) 1, no additions; 2, 0.7 mM zinc acetate;…”

Interprotein metal exchange between transcription factor IIIa and apo-metallothionein

“…Then, Wilcox and coworkers [27] showed directly that a single Zn-finger from Sp1 reacted with the α-domain of metallothionein through a ligandsubstitution process. Similarly, Roesijadi and coworkers [28] recently observed that apoMT reacted with another C 2 H 2 Zn-finger peptide, Tramtrack, resulting in the inactivation of its capacity to bind to DNA.…”

“…More recently, two reports have described chemical properties of the reaction of selected Znfinger peptides with apoMT or the α-domain of metallothionein [27,28]. The present experiments were undertaken to gain insight into the chemical properties of the reaction of Zn-TFIIIA with apoMT.…”

Cadmium and lead interactions with transcription factor IIIA from Xenopus laevis: a model for zinc finger protein reactions with toxic metal ions and metallothionein

“…Buffer: 20 mM HEPES, pH 7, 25°C. a Abbreviations and references: Sp1 (F3), finger 3 of Sp1 transcription factor (Posewitz & Wilcox, 1995), CP1, consensus peptide derived from available sequences of N 2 S 2 domains (Krizek, Merkle & Berg, 1993).…”