Kankia Besik I, Barany George, Musier-Forsyth Karin
Department of Chemistry, University of Minnesota, Minneapolis, MN 55455, USA.
Nucleic Acids Res. 2005 Aug 2;33(14):4395-403. doi: 10.1093/nar/gki741. Print 2005.
The human immunodeficiency virus type 1 nucleocapsid protein (NC) is a nucleic acid chaperone that catalyzes the rearrangement of nucleic acids into their thermodynamically most stable structures. In the present study, a combination of optical and thermodynamic techniques were used to characterize the influence of NC on the secondary structure, thermal stability and energetics of monomolecular DNA quadruplexes formed by the sequence d(GGTTGGTGTGGTTGG) in the presence of K+ or Sr2+. Circular dichroism studies demonstrate that NC effectively unfolds the quadruplexes. Studies carried out with NC variants suggest that destabilization is mediated by the zinc fingers of NC. Calorimetric studies reveal that NC destabilization is enthalpic in origin, probably owing to unstacking of the G-quartets upon protein binding. In contrast, parallel studies performed on a related DNA duplex reveal that under conditions where NC readily destabilizes and unfolds the quadruplexes, its effect on the DNA duplex is much less pronounced. The differences in NC's ability to destabilize quadruplex versus duplex is in accordance with the higher DeltaG of melting for the latter, and with the inverse correlation between nucleic acid stability and the destabilizing activity of NC.
人类免疫缺陷病毒1型核衣壳蛋白（NC）是一种核酸伴侣蛋白，可催化核酸重排为其热力学上最稳定的结构。在本研究中，采用光学和热力学技术相结合的方法，来表征在存在K⁺或Sr²⁺的情况下，NC对由序列d（GGTTGGTGTGGTTGG）形成的单分子DNA四链体的二级结构、热稳定性和能量学的影响。圆二色性研究表明，NC能有效地使四链体解折叠。对NC变体进行的研究表明，去稳定作用是由NC的锌指介导的。量热研究表明，NC的去稳定作用起源于焓，这可能是由于蛋白质结合后G-四联体的堆积被破坏。相比之下，对相关DNA双链体进行的平行研究表明，在NC能轻易使四链体去稳定并解折叠的条件下，其对DNA双链体的影响要小得多。NC使四链体与双链体去稳定的能力差异，与后者较高的解链ΔG一致，也与核酸稳定性和NC的去稳定活性之间的负相关一致。
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