Stillman Timothy J, Upadhyay Manisha, Norte Valia A, Sedelnikova Svetlana E, Carradus Maria, Tzokov Svetomir, Bullough Per A, Shearman Claire A, Gasson Michael J, Williams Colin H, Artymiuk Peter J, Green Jeffrey
Krebs Institute for Biomolecular Research, Department of Molecular Biology and Biotechnology, Firth Court, Western Bank, University of Sheffield, Sheffield S10 2TN, UK.
Mol Microbiol. 2005 Aug;57(4):1101-12. doi: 10.1111/j.1365-2958.2005.04757.x.
Dps proteins play a major role in the protection of bacterial DNA from damage by reactive oxygen species. Previous studies have implicated the extended lysine-containing N-terminal regions of Dps subunits in DNA binding, but this part of the structure has not previously been observed crystallographically. Here the structures of two Dps proteins (DpsA and DpsB) from Lactococcus lactis MG1363 reveal for the first time the presence of an N-terminal alpha helix that extends from the core of the Dps subunit. Consequently, the N-terminal helices are displayed in parallel pairs on the exterior of the dodecameric Dps assemblies. Both DpsA and DpsB bind DNA. Deletion of the DpsA N-terminal helix impaired DNA binding. The N-terminal Lys residues of Escherichia coli Dps have been implicated in DNA binding. Replacement of the lactococcal DpsA Lys residues 9, 15 and 16 by Glu did not inhibit DNA binding. However, DNA binding was inhibited by EDTA, suggesting a role for cations in DNA binding. In contrast to E. coli, Bacillus brevis and Mycobacterium smegmatis Dps:DNA complexes, in which DNA interacts with crystalline Dps phases, L. lactis DNA:Dps complexes appeared as non-crystalline aggregates of protein and DNA in electron micrographs.
Dps蛋白在保护细菌DNA免受活性氧损伤方面发挥着重要作用。先前的研究表明，Dps亚基含赖氨酸的延伸N端区域参与DNA结合，但该结构部分此前尚未通过晶体学观察到。在此，来自乳酸乳球菌MG1363的两种Dps蛋白（DpsA和DpsB）的结构首次揭示了从Dps亚基核心延伸出的N端α螺旋的存在。因此，N端螺旋以平行对的形式展示在十二聚体Dps组装体的外部。DpsA和DpsB都能结合DNA。删除DpsA的N端螺旋会损害DNA结合。大肠杆菌Dps的N端赖氨酸残基与DNA结合有关。用谷氨酸取代乳酸乳球菌DpsA的赖氨酸残基9、15和16并不抑制DNA结合。然而，DNA结合受到EDTA的抑制，表明阳离子在DNA结合中起作用。与大肠杆菌、短短芽孢杆菌和耻垢分枝杆菌的Dps:DNA复合物不同，在这些复合物中DNA与结晶Dps相相互作用，在电子显微镜下，乳酸乳球菌的DNA:Dps复合物表现为蛋白质和DNA的非晶聚集体。
