Structures and functions of new copper receptor proteins controlling gene regulation and metal trafficking

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Copper serves as a cofactor for many proteins and enzymes involved in important biological processes, but at the same time, excessive copper is toxic to cell. Thus, the intracellular copper concentration must be tightly controlled such that copper is provided to essential enzymes but does not accumulate to toxic levels. As a result, organisms have evolved various mechanisms to obtain and distribute copper safely. The thesis represents a structural-based investigation into copper receptor proteins involved in copper homeostasis, including copper regulator CueR, copper chaperones CusF and Atx1. The major technique is X-ray crystallography. CueR is one member of MerR family metalloregulatory proteins and controls the transcription of genes involved in copper detoxification in E.coli. The structures of metal bound forms of CueR, combined with the zinc regulator ZntR of the same family, elucidated the unusual metal coordination environment accounting for the extraordinary metal responsiveness and metal selectivity. The mutational study was consistent with the observation from structural models. Biochemical and biophysical investigations of the binding of CueR and its responsive promoters revealed important minor groove interaction crucial for protein-DNA recognition. Extensive trials to cocrystallize CueR-DNA complex finally led to the very recent intriguing breakthrough, which will eventually produce the structural model of CueR/DNA complex. CusF is a small periplasmic protein thought to function as part of the cus copper tolerance system. The structure characterized a Cu(I) center coordinated with Met-rich motif. It also revealed a Trp close to the metal center at a remarkable distance, suggesting the existence of cation-p interaction, which has been recently confirmed the Resonance Raman spectroscopic data from Dr. Anna Davis. Atx1 is a small cytosolic copper chaperone in yeast, and has been characterized extensively. It was utilized to investigate the interaction between tetrathiomolybdate (TM) and copper proteins. The structure was solved by MR and Cu-MAD. The model presented the first structural demonstration of the protein-Cu-TM complex. It elucidated the binding mechanism between TM and Cu-Atx1, and revealed how the versatile inorganic Mo-Cu cluster adapted to a biological environment. It greatly deepens the understanding of the classical Mo-Cu antagonism and provides new insights into TM as a potential anti-cancer drug.

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  • 09/06/2018
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