Chechik Maria, Greive Sandra J, Antson Alfred A, Jenkins Huw T
York Structural Biology Laboratory, Department of Chemistry, University of York, York YO10 5DD, United Kingdom.
York Biomedical Research Institute, University of York, York YO10 5NG, United Kingdom.
Proc Natl Acad Sci U S A. 2024 Aug 13;121(33):e2406138121. doi: 10.1073/pnas.2406138121. Epub 2024 Aug 8.
DNA recognition is critical for assembly of double-stranded DNA viruses, particularly for the initiation of packaging the viral genome into the capsid. The key component that recognizes viral DNA is the small terminase protein. Despite prior studies, the molecular mechanism for DNA recognition remained elusive. Here, we address this question by identifying the minimal site in the bacteriophage HK97 genome specifically recognized by the small terminase and determining the structure of this complex by cryoEM. The circular small terminase employs an entirely unexpected mechanism in which DNA transits through the central tunnel, and sequence-specific recognition takes place as it emerges. This recognition stems from a substructure formed by the N- and C-terminal segments of two adjacent protomers which are unstructured when DNA is absent. Such interaction ensures continuous engagement of the small terminase with DNA, enabling it to slide along the DNA while simultaneously monitoring its sequence. This mechanism allows locating and instigating packaging initiation and termination precisely at the specific sequence.
DNA识别对于双链DNA病毒的组装至关重要，特别是在将病毒基因组包装到衣壳的起始阶段。识别病毒DNA的关键成分是小末端酶蛋白。尽管之前有研究，但DNA识别的分子机制仍然难以捉摸。在这里，我们通过鉴定噬菌体HK97基因组中被小末端酶特异性识别的最小位点，并通过冷冻电镜确定该复合物的结构来解决这个问题。环状小末端酶采用了一种完全意想不到的机制，即DNA穿过中央通道，序列特异性识别在其出现时发生。这种识别源于两个相邻原体的N端和C端片段形成的亚结构，在没有DNA时这些片段是无结构的。这种相互作用确保了小末端酶与DNA的持续结合，使其能够沿着DNA滑动，同时监测其序列。这种机制允许在特定序列处精确地定位和启动包装起始和终止。
