Z-DNA

Z-DNA又称Z型DNA，是DNA双螺旋结构的一种形式，具有左旋型态的双股螺旋（与常见的B-DNA相反），并呈现锯齿形状。Z-DNA为三种具生物活性的DNA双螺旋结构之一，另两种为A-DNA与B-DNA。

历史[编辑]

Z-DNA为首先于1979年被解出晶体结构的DNA型态，研究者为麻省理工大学的Alexander Rich等人^[1]。B型及Z型相互结合时的结晶则解于2005年^[2]，使科学家了解Z-DNA在细胞中的潜在角色，当一段Z-DNA形成时，其两端必为B-Z相互结合型态，形成与B-DNA的界面。

Z-DNA的双股螺旋为左旋型态，与B-DNA的右旋型态明显有所差别。其结构每两个碱基对重复出现一次。大小螺旋凹槽之间的差别较A型及B型小，只在宽度上有些微差异。这种型态并不常见，但某些特定情况可增加其存在的可能，如嘌呤-嘧啶交替序列、DNA超螺旋，或盐分与某些阳离子浓度高时。

Z-DNA能够与B-DNA构成相互结合型态，这种结构会使一对碱基突出于双螺旋之外。

几何属性	A-DNA	B-DNA	Z-DNA
螺旋方向	右旋	右旋	左旋
重复单元	1 bp	1 bp	2 bp
Rotation/bp	32.7°	35.9°	60°/2
bp/turn	10	11	12
Inclination of bp to axis	+19°	−1.2°	−9°
Rise/bp along axis	2.3 Å (0.23 nm)	3.32 Å (0.332 nm)	3.8 Å (0.38 nm)
Pitch/turn of helix	28.2 Å (2.82 nm)	33.2 Å (3.32 nm)	45.6 Å (4.56 nm)
Mean propeller twist	+18°	+16°	0°
糖基角度	anti	anti	C: anti, G: syn
Sugar pucker	C3'-endo	C2'-endo	C: C2'-endo, G: C3'-endo
直径	23 Å (2.3 nm)	20 Å (2.0 nm)	18 Å (1.8 nm)
来源:^[3]^[4]^[5]

^ Wang AHJ, Quigley GJ, Kolpak FJ, Crawford JL, van Boom JH, Van der Marel G, Rich A. Molecular structure of a left-handed double helical DNA fragment at atomic resolution. Nature (London). 1979, 282: 680–686. PMID 514347
^ Ha SC, Lowenhaupt K, Rich A, Kim YG, Kim KK. Crystal structure of a junction between B-DNA and Z-DNA reveals two extruded bases. Nature. 2005, 437: 1183–1186. PMID 16237447.
^ Sinden, Richard R. DNA structure and function 1st. Academic Press. 1994-01-15: 398. ISBN 0-126-45750-6.
^ Rich A, Norheim A, Wang AHJ. The chemistry and biology of left-handed Z-DNA. Annual Review of Biochemistry. 1984, 53 (1): 791–846. PMID 6383204. doi:10.1146/annurev.bi.53.070184.004043.
^ Ho PS. The non-B-DNA structure of d(CA/TG)n does not differ from that of Z-DNA. Proc Natl Acad Sci USA. 1994-09-27, 91 (20): 9549–9553. Bibcode:1994PNAS...91.9549H. PMC 44850 . PMID 7937803. doi:10.1073/pnas.91.20.9549.

Sinden RR (1994). DNA structure and function. Academic Press, 179-216. ISBN 978-0-12-645750-6
Rich A, Zhang S (2003). Timeline: Z-DNA: the long road to biological function. Nat Rev Genet, 4:566–572.