Targeting Zinc Finger Proteins with Exogenous Metals and Molecules: Lessons Learned from Tristetraprolin, a CCCH type Zinc Finger

Pharmaceutical Sciences ; University of Maryland, Baltimore ; Ph.D. ; Zinc (Zn) plays a key role in inflammatory response, including regulating the nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) signaling pathway. Among the signaling proteins involved in the NF-κB pathway, many are known zinc finger proteins (ZFs), including Tristetraprolin (TTP). TTP is a non-classical CCCH-type Zinc Finger protein (ZF), that contains two Cys3His zinc binding domains and is a key regulator of the inflammatory response. TTP is a potential target for exogenous gold (Au) and copper (Cu), as well as hydrogen sulfide, an emerging gasotransmitter. To understand how TTP is targeted by other metals, the interactions of TTP were investigated using a combination of bioinorganic chemistry tools including as optical spectroscopy, native electrospray ionization mass spectrometry (ESI-MS), and X-ray absorption study (XAS). The first metal investigated was Cu(I). I discovered that Cu(I) can bind to the tandem ZF construct of TTP (TTP-2D) and disrupt structure and function. This finding indicates a potential relationship between Cu toxicity and metal-regulation of ZFs. The second metal investigated was Au(III). I discovered that the reactivity of TTP-2D with gold complex leads to Au exchange forming a series of Aux-TTP-2D complexes, with reduction of the gold from Au(III) to Au(I). These protein species are then functionally inactive (no RNA binding). When the same experiments were performed with TTP bound to RNA, the Zn-TTP/RNA complex is not disrupted by the Au-complex suggesting a protective role for RNA. To understand how H2S, a signaling molecule, targets Zn-TTP-2D, its reactivity was determined using a combination of cryo-ESI-MS, fluorescence, and electron paramagnetic resonance (EPR) spectroscopies. We found that the H2S oxidizes the cysteine residues of Zn-TTP via a mechanism that involves atmospheric oxygen, a persulfide intermediate and a radical reaction. The results of these biochemical studies of TTP will ...