Kwon Eunju, Pathak Deepak, Chang Hyeun Wook, Kim Dong Young
College of Pharmacy, Yeungnam University, Gyeongsan, Gyeongbuk, South Korea.
PLoS One. 2017 Aug 1;12(8):e0182382. doi: 10.1371/journal.pone.0182382. eCollection 2017.
Cytosine deamination induced by stresses or enzymatic catalysis converts deoxycytidine into deoxyuridine, thereby introducing a G to A mutation after DNA replication. Base-excision repair to correct uracil to cytosine is initiated by uracil-DNA glycosylase (UDG), which recognizes and eliminates uracil from DNA. Mimivirus, one of the largest known viruses, also encodes a distinctive UDG gene containing a long N-terminal domain (N-domain; residues 1-130) and a motif-I (residues 327-343), in addition to the canonical catalytic domain of family I UDGs (also called UNGs). To understand the structural and functional features of the additional segments, we have determined the crystal structure of UNG from Acanthamoeba polyphaga mimivirus (mvUNG). In the crystal structure of mvUNG, residues 95-130 in the N-domain bind to a hydrophobic groove in the catalytic domain, and motif-I forms a short β-sheet with a positively charged surface near the active site. Circular dichroism spectra showed that residues 1-94 are in a random coil conformation. Deletion of the three additional fragments reduced the activity and thermal stability, compared to full-length mvUNG. The results suggested that the mvUNG N-domain and motif-I are required for its structural and functional integrity.
由压力或酶催化诱导的胞嘧啶脱氨作用将脱氧胞苷转化为脱氧尿苷，从而在DNA复制后引入从鸟嘌呤到腺嘌呤的突变。尿嘧啶-DNA糖基化酶（UDG）启动碱基切除修复以将尿嘧啶校正为胞嘧啶，该酶可识别并从DNA中消除尿嘧啶。米米病毒是已知最大的病毒之一，除了I型UDG（也称为UNG）的典型催化结构域外，它还编码一个独特的UDG基因，该基因包含一个长的N端结构域（N结构域；第1至130位氨基酸残基）和一个基序I（第327至343位氨基酸残基）。为了了解这些额外片段的结构和功能特征，我们确定了多噬棘阿米巴米米病毒（mvUNG）的UNG晶体结构。在mvUNG的晶体结构中，N结构域中的第95至130位氨基酸残基与催化结构域中的一个疏水凹槽结合，基序I在活性位点附近形成一个带有带正电表面的短β折叠。圆二色光谱表明，第1至94位氨基酸残基呈无规卷曲构象。与全长mvUNG相比，删除这三个额外片段会降低其活性和热稳定性。结果表明，mvUNG的N结构域和基序I对其结构和功能完整性是必需的。
