Structural Studies of E73 from a Hyperthermophilic Archaeal Virus Identify the 鈥淩H3鈥?Domain, an Elaborated Ribbon鈥揌elix鈥揌elix Motif Involved in DNA Recognition
详细信息 查看全文
- 作者：Casey Schlenker ; Anupam Goel ; Brian P. Tripet ; Smita Menon ; Taylor Willi ; Mensur Dlaki膰 ; Mark J. Young ; C. Martin Lawrence ; Val茅rie Copi茅
- 刊名：Biochemistry
- 出版年：2012
- 出版时间：April 3, 2012
- 年：2012
- 卷：51
- 期：13
- 页码：2899-2910
- 全文大小：471K
- 年卷期：v.51,no.13(April 3, 2012)
- ISSN：1520-4995
文摘
Hyperthermophilic archaeal viruses, including Sulfolobus spindle-shaped viruses (SSVs) such as SSV-1 and SSV-Ragged Hills, exhibit remarkable morphology and genetic diversity. However, they remain poorly understood, in part because their genomes exhibit limited or unrecognizable sequence similarity to genes with known function. Here we report structural and functional studies of E73, a 73-residue homodimeric protein encoded within the SSV-Ragged Hills genome. Despite lacking significant sequence similarity, the nuclear magnetic resonance (NMR) structure reveals clear similarity to ribbon鈥揾elix鈥揾elix (RHH) domains present in numerous proteins involved in transcriptional regulation. In vitro double-stranded DNA (dsDNA) binding experiments confirm the ability of E73 to bind dsDNA in a nonspecific manner with micromolar affinity, and characterization of the K11E variant confirms the location of the predicted DNA binding surface. E73 is distinct, however, from known RHH domains. The RHH motif is elaborated upon by the insertion of a third helix that is tightly integrated into the structural domain, giving rise to the 鈥淩H3鈥?fold. Within the homodimer, this helix results in the formation of a conserved, symmetric cleft distal to the DNA binding surface, where it may mediate protein鈥損rotein interactions or contribute to the high thermal stability of E73. Analysis of backbone amide dynamics by NMR provides evidence of a rigid core, fast picosecond to nanosecond time scale NH bond vector motions for residues located within the antiparallel 尾-sheet region of the proposed DNA-binding surface, and slower microsecond to millisecond time scale motions for residues in the 伪1鈭捨? loop. The roles of E73 and its SSV homologues in the viral life cycle are discussed.