Structural Stability Analysis of the Cytidine Deaminase Superfamily members

• Main Authors: Yi-Chian Chen, 陳宜謙
• Other Authors: Shwu-Huey Liaw
• Format: Others
• Language: zh-TW
• Published: 2006
• Online Access: http://ndltd.ncl.edu.tw/handle/76201942883165509474

碩士 === 國立陽明大學 === 生化暨分子生物研究所 === 94 === There are a variety of deaminases that function as deaminating the purine or pyrimidine bases of nucleotides. Theses enzymes share a common fold and hence they are grouped as the cytidine deaminase superfamily. All the members possess a common Zn2+-assisted deamination activity with a consensus zinc-binding signature, H(C)XE and PCX2-9C. The members include the mononucleotide deaminases involved in nucleotide metabolism, and the RNA(DNA)-editing deaminases involved in gene diversity and in anti-virus defense. In this thesis, the member structures are compared to reveal the structural divergence, which should lead to not only the substrate specificity but also the distinct structural stability. The five target proteins include Methanosarcina mazei MM3105，Bacillus subtilis guanine deaminase and RibG protein, yeast cytosine deaminase, and mouse APOBEC2. Heat, urea or guanidine hydrochloride is used to carry out the protein unfolding experiments. Fluorescence and circular dichroism spectrometry are then employed to monitor the unfolding process. The results indicate that MM3105 is the most stable while yeast cytosine deaminase is the least. The four-helix bundle in MM3105 is suggested to largely enhance the structural stability, as well as the C-terminal domain swapping in B. subtilis guanine deaminase, and tetramerization in B. subtilis RibG. Finally, mouse APOBEC2 is identified as the first monomeric member. This protein does not contain any significant deaminase activity, so it might have evolved as a monomer to adapt to its particular function. Mammalian APOBEC2 is predicted to contain a four-helix bundle as MM3105, which can enhance the stability of the monomeric structure.