Basu Debashree, Khare Garima, Singh Shashi, Tyagi Anil, Khosla Sanjeev, Mande Shekhar C
Laboratory of Structural Biology, Centre for DNA Fingerprinting and Diagnostics, Hyderabad 500001, India.
Nucleic Acids Res. 2009 Aug;37(15):4944-54. doi: 10.1093/nar/gkp502. Epub 2009 Jun 15.
The Mycobacterium tuberculosis genome sequence reveals remarkable absence of many nucleoid-associated proteins (NAPs), such as HNS, Hfq or DPS. In order to characterize the nucleoids of M. tuberculosis, we have attempted to identify NAPs, and report an interesting finding that a chaperonin-homolog, GroEL1, is nucleoid associated. We report that M. tuberculosis GroEL1 binds DNA with low specificity but high affinity, suggesting that it might have naturally evolved to bind DNA. We are able to demonstrate that GroEL1 can effectively function as a DNA-protecting agent against DNase I or hydroxyl-radicals. Moreover, Atomic Force Microscopic studies reveal that GroEL1 can condense a large DNA into a compact structure. We also provide in vivo evidences that include presence of GroEL1 in purified nucleoids, in vivo crosslinking followed by Southern hybridizations and immunofluorescence imaging in M. tuberculosis confirming that GroEL1: DNA interactions occur in natural biological settings. These findings therefore reveal that M. tuberculosis GroEL1 has evolved to be associated with nucleoids.
结核分枝杆菌基因组序列显示，许多类核相关蛋白（NAPs），如HNS、Hfq或DPS明显缺失。为了表征结核分枝杆菌的类核，我们试图鉴定NAPs，并报告了一个有趣的发现，即一种伴侣蛋白同源物GroEL1与类核相关。我们报告说，结核分枝杆菌GroEL1以低特异性但高亲和力结合DNA，这表明它可能在自然进化过程中获得了结合DNA的能力。我们能够证明，GroEL1可以有效地作为一种抗DNase I或羟基自由基的DNA保护剂。此外，原子力显微镜研究表明，GroEL1可以将大片段DNA浓缩成紧密的结构。我们还提供了体内证据，包括纯化类核中存在GroEL1、体内交联后进行Southern杂交以及结核分枝杆菌中的免疫荧光成像，证实了GroEL1与DNA的相互作用发生在自然生物环境中。因此，这些发现揭示了结核分枝杆菌GroEL1已经进化到与类核相关。
