エネルギー理工学研究所講演会

エネルギー理工学研究所講演会
講師：Joon-Hwa Lee 教授（Department of Chemistry, Gyeongsang National University）
（エネルギー理工学研究所・外国人客員教授）
題目：NMR Study of the Protein-induced B-Z Conformational Change of Nucleic Acids
日時：平成 28 年 10 月 25 日（火）16:00 - 17:00
場所：本館Ｎ２７３Ｅセミナー室
問い合わせ先：エネルギー理工学研究所・片平正人([email protected])
要旨：
Z-DNA is a higher energy conformation than right-handed B-DNA and can be stabilized by high salt, negative
supercoiling, and complex formation with Z-DNA binding proteins (ZBPs). The ZBPs have been identified in a
family of proteins including the human RNA editing enzyme (ADAR1), the mammalian DNA-dependent
activator of interferon-regulatory factor (DAI), poxviral E3L protein, and fish ZBP-containing protein kinase
(PKZ). The crystal structures of various ZBPs in complexes with 6-base-paired (6-bp) DNA revealed that two Zα
proteins bind to each strand of double-stranded (ds) Z-DNA with twofold symmetry with respect to the DNA
helical axis. In order to understand how ZBPs specifically recognize Z-DNA sequence in a sea of B-DNA, we
performed NMR experiments with complexes of ZαADAR1 bound to d(CG)3 produced at a variety of
protein-to-DNA molar ratios. From this study, we suggested an active B-Z transition mechanism in which the
ZαADAR1 first binds to B-DNA and then converts it to left-handed Z-DNA, a conformation that is then stabilized
by the additional binding of a second ZαADAR1 molecule (Fig. 1).
When Z-DNA is formed in a long genomic DNA by ZBP, two B-Z junctions are produced with the extrusion of
one base pair from each junction. To answer the question of how ZBPs induce B-Z transitions in CG-rich
segments while maintaining the B-conformation of surrounding segments, we investigated the kinetics and
thermodynamics of base-pair openings of a 13-bp DNA in complex with ZαADAR1. Our study also suggest a
three-step mechanism of B−Z junction formation: (i) ZαADAR1 specifically interacts with a CG-rich DNA segment
maintaining B-form helix via a unique conformation; (ii) the neighboring AT-rich region becomes very unstable,
and the CG-rich DNA segment is easily converted to Z-DNA; and (iii) the AT-rich regions are base-paired again,
and the B-Z junction structure is formed (Fig. 2).
The ZαADAR1 domain also binds to Z-RNA and then enhances the editing level of dsRNA by ADAR1. Despite
the structural study of ZαADAR1 for Z-RNA, the detailed molecular mechanism by which ZαADAR1 converts a
right-handed A-form structure in an RNA duplex to a left-handed Z-form is not well understood. Here, we are
undergoing to carry out the NMR study of ZαADAR1 complexed with a 6-bp RNA duplex r(CG)3 at a variety of
protein-to-RNA molar ratios and these results were compared to those of DNA substrate, d(CG)3.
References:
1) Kang, Y.-M. et al. (2009) J. Am. Chem. Soc. 131, 11485.
2) Lee, Y.-M. et al. (2012) J. Am. Chem. Soc. 134, 5276.
3) Lee, A.-R. et al. (2016) Nucleic Acids Res. 44, 2936.

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