Gamsjaeger Roland, Kariawasam Ruvini, Gimenez Adrian X, Touma Christine, McIlwain Elysse, Bernardo Ray E, Shepherd Nicholas E, Ataide Sandro F, Dong Qihan, Richard Derek J, White Malcolm F, Cubeddu Liza
*School of Science and Health, University of Western Sydney, Penrith, NSW 2751, Australia.
†School of Molecular Bioscience, University of Sydney, Sydney, NSW 2006, Australia.
Biochem J. 2015 Jan 15;465(2):337-46. doi: 10.1042/BJ20141140.
Canonical single-stranded DNA-binding proteins (SSBs) from the oligosaccharide/oligonucleotide-binding (OB) domain family are present in all known organisms and are critical for DNA replication, recombination and repair. The SSB from the hyperthermophilic crenarchaeote Sulfolobus solfataricus (SsoSSB) has a 'simple' domain organization consisting of a single DNA-binding OB fold coupled to a flexible C-terminal tail, in contrast with other SSBs in this family that incorporate up to four OB domains. Despite the large differences in the domain organization within the SSB family, the structure of the OB domain is remarkably similar all cellular life forms. However, there are significant differences in the molecular mechanism of ssDNA binding. We have determined the structure of the SsoSSB OB domain bound to ssDNA by NMR spectroscopy. We reveal that ssDNA recognition is modulated by base-stacking of three key aromatic residues, in contrast with the OB domains of human RPA and the recently discovered human homologue of SsoSSB, hSSB1. We also demonstrate that SsoSSB binds ssDNA with a footprint of five bases and with a defined binding polarity. These data elucidate the structural basis of DNA binding and shed light on the molecular mechanism by which these 'simple' SSBs interact with ssDNA.
来自寡糖/寡核苷酸结合（OB）结构域家族的典型单链DNA结合蛋白（SSB）存在于所有已知生物体中，对DNA复制、重组和修复至关重要。嗜热泉古菌硫磺硫杆菌（Sulfolobus solfataricus）的SSB（SsoSSB）具有“简单”的结构域组织，由单个与柔性C末端尾巴相连的DNA结合OB折叠组成，这与该家族中包含多达四个OB结构域的其他SSB形成对比。尽管SSB家族内的结构域组织存在很大差异，但OB结构域的结构在所有细胞生命形式中都非常相似。然而，在单链DNA结合的分子机制上存在显著差异。我们通过核磁共振光谱法确定了与单链DNA结合的SsoSSB OB结构域的结构。我们发现，与人类RPA的OB结构域以及最近发现的SsoSSB的人类同源物hSSB1不同，单链DNA的识别是由三个关键芳香族残基的碱基堆积调节的。我们还证明，SsoSSB以五个碱基的足迹和确定的结合极性结合单链DNA。这些数据阐明了DNA结合的结构基础，并揭示了这些“简单”SSB与单链DNA相互作用的分子机制。
