Single Molecule Force Spectroscopy Reveals Unfolding Mechanism and Energy Landscape of a Metal-induced Folding Protein
【摘要】：Protein is an essential bio-molecule which participates in almost every aspect of life.To function properly, most proteins need fold into three dimensional structure correctly with certain stability after translation. This folding process can be driven by weak intermolecular interactions, such as hydrophobic interaction, hydrogen bonding,salt bridge. It is noted that metal ion can also be an important cofactor to facilitate protein folding and enhance its stability. The formation of metal-ligand bonds between metal ions and protein residues connect different parts of protein and stabilizes the folding structure significantly. Indeed for some proteins, metal ion can be the dominate factor for folding. In this study, we use atomic force microscopy(AFM) based single molecule force spectroscopy to directly study the unfolding process of such a protein metallothionein(MT) and its stability. MT has twenty cysteines and can bind seven cadmium ions. It forms one Cd3 S9 and one Cd4 S11 metal cluster into two domains, respectively. From the single molecule experiment, we observed multiple unfolding pathways of MT resulting from the rupture of different combinations and sequences of Cd-S bonds. Moreover, we discovered the dominate two-step bond rupture scenarios of each domain and quantify their energy landscape.Our result not only provides new insight for metalloprotein structure and stability but also demonstrates the potential of AFM as a novel and complementary tool to study metalloprotein.