Spectroscopic Determination of the Thermodynamics of Cobalt and Zinc Binding to GATA Proteins

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Abstract

Vertebrate GATA proteins regulate processes that are vital to development, and each possesses two tandem GATA finger domains: an N-terminal GATA finger and a C-terminal GATA finger. These GATA fingers require Zn(2+) to fold, to bind DNA recognition elements, and to regulate transcription. While the GATA-1 C-terminal finger is necessary and sufficient to bind to single GATA DNA sites, the N-terminal finger interacts with DNA such that the double finger unit (DF domain) has a binding and transactivation profile that is tuned by the DNA-binding site. Co(2+) was used as a spectroscopic probe in a series of competition titrations to determine the affinity of Co(2+) and Zn(2+) for the C-terminal finger from chicken GATA-1 and the double finger from human GATA-1 (referred to in this report as CF and DF). For CF, these experiments yielded K(b)(Co) = 1.0 (+/-1.3) x 10(7) M(-1) and K(b)(Zn) = 2.0 (+/-1.3) x 10(10) M(-1). For DF, these experiments yielded equilibrium constants for the process of two M(2+) binding to form M(2+)(2)-DF of beta(2)(Co) = 2.5 (+/-1.6) x 10(14) M(-2) and beta(2)(Zn) = 6.3 (+/-2.5) x 10(20) M(-2). The ZnS(4) coordination environment of Zn(2+)-bound CF was confirmed with X-ray absorption spectroscopy. A detailed analysis of these data suggests that the N-terminal and C-terminal fingers of DF act as independent and identical Zn(2+)-binding sites and each finger binds Zn(2+) with an affinity equivalent to that of CF.

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