Cadmium Exchange with Zinc in the Non-Classical Zinc Finger Protein Tristetraprolin.

Tristetraprolin (TTP) is a nonclassical CCCH zinc finger protein that regulates inflammation. TTP targets AU-rich RNA sequences of cytokine mRNAs forming a TTP/mRNA complex. This complex is then degraded, switching off the inflammatory response. Cadmium, a known carcinogen, triggers proinflammatory effects, and there is evidence that Cd increases TTP expression in cells, suggesting that Zn-TTP may be a target for cadmium toxicity. We sought to determine whether Cd exchanges with Zn in the TTP active site and measure the effect of RNA binding on this exchange. A construct of TTP that contains the two CCCH domains (TTP-2D) was employed to investigate these interactions. A spin-filter ICP-MS experiment to quantify the metal that is bound to the ZF after metal exchange was performed, and it was determined that Cd exchanges with Zn in Zn-TTP-2D and that Zn exchanges with Cd in Cd-TTP-2D. A native ESI-MS experiment to identify the metal-ZF complexes formed after metal exchange was performed, and M-TTP-2D complexes with singular and double metal exchange were observed. Metal exchange was measured in both the absence and presence of TTP's partner RNA, with retention of RNA binding. These data show that Cd can exchange with Zn in TTP without affecting function.