Robinson H, Gao Y G, McCrary B S, Edmondson S P, Shriver J W, Wang A H
Department of Cell and Structural Biology, University of Illinois at Urbana-Champaign, Urbana 61801, USA.
Nature. 1998 Mar 12;392(6672):202-5. doi: 10.1038/32455.
The proteins Sac7d and Sso7d belong to a class of small chromosomal proteins from the hyperthermophilic archaeon Sulfolobus acidocaldarius and S. solfactaricus, respectively. These proteins are extremely stable to heat, acid and chemical agents. Sac7d binds to DNA without any particular sequence preference and thereby increases its melting temperature by approximately 40 degrees C. We have now solved and refined the crystal structure of Sac7d in complex with two DNA sequences to high resolution. The structures are examples of a nonspecific DNA-binding protein bound to DNA, and reveal that Sac7d binds in the minor groove, causing a sharp kinking of the DNA helix that is more marked than that induced by any sequence-specific DNA-binding proteins. The kink results from the intercalation of specific hydrophobic side chains of Sac7d into the DNA structure, but without causing any significant distortion of the protein structure relative to the uncomplexed protein in solution.
蛋白质Sac7d和Sso7d分别属于来自嗜热古菌嗜酸热硫化叶菌和嗜热栖热菌的一类小染色体蛋白。这些蛋白质对热、酸和化学试剂具有极高的稳定性。Sac7d可无特定序列偏好地与DNA结合，从而使其解链温度提高约40摄氏度。我们现已解析并精修了Sac7d与两条DNA序列复合物的晶体结构，分辨率很高。这些结构是与DNA结合的非特异性DNA结合蛋白的实例，揭示了Sac7d结合在小沟中，导致DNA螺旋急剧扭结，这种扭结比任何序列特异性DNA结合蛋白诱导的扭结更为明显。这种扭结是由Sac7d特定的疏水侧链插入DNA结构引起的，但相对于溶液中未复合的蛋白质，蛋白质结构没有发生任何显著扭曲。
