Li Dawei, Zhao Rui, Lilyestrom Wayne, Gai Dahai, Zhang Rongguang, DeCaprio James A, Fanning Ellen, Jochimiak Andrzej, Szakonyi Gerda, Chen Xiaojiang S
Department of Biochemistry and Molecular Genetics, University of Colorado Health Science Center, School of Medicine, Denver, Colorado 80262, USA.
Nature. 2003 May 29;423(6939):512-8. doi: 10.1038/nature01691.
The oncoprotein large tumour antigen (LTag) is encoded by the DNA tumour virus simian virus 40. LTag transforms cells and induces tumours in animals by altering the functions of tumour suppressors (including pRB and p53) and other key cellular proteins. LTag is also a molecular machine that distorts/melts the replication origin of the viral genome and unwinds duplex DNA. LTag therefore seems to be a functional homologue of the eukaryotic minichromosome maintenance (MCM) complex. Here we present the X-ray structure of a hexameric LTag with DNA helicase activity. The structure identifies the p53-binding surface and reveals the structural basis of hexamerization. The hexamer contains a long, positively charged channel with an unusually large central chamber that binds both single-stranded and double-stranded DNA. The hexamer organizes into two tiers that can potentially rotate relative to each other through connecting alpha-helices to expand/constrict the channel, producing an 'iris' effect that could be used for distorting or melting the origin and unwinding DNA at the replication fork.
癌蛋白大肿瘤抗原（LTag）由DNA肿瘤病毒猴病毒40编码。LTag通过改变肿瘤抑制因子（包括pRB和p53）及其他关键细胞蛋白的功能来转化细胞并在动物体内诱发肿瘤。LTag还是一种分子机器，可扭曲/解旋病毒基因组的复制起点并解开双链DNA。因此，LTag似乎是真核微型染色体维持（MCM）复合体的功能同源物。在此，我们展示了具有DNA解旋酶活性的六聚体LTag的X射线结构。该结构确定了p53结合表面，并揭示了六聚化的结构基础。六聚体包含一个长的带正电荷通道，其具有异常大的中央腔室，可结合单链和双链DNA。六聚体组织成两层，这两层可能通过连接α螺旋彼此相对旋转，以扩展/收缩通道，产生一种“虹膜”效应，可用于扭曲或解旋复制起点并在复制叉处解开DNA。
