Eijkelenboom A P, van den Ent F M, Vos A, Doreleijers J F, Hård K, Tullius T D, Plasterk R H, Kaptein R, Boelens R
Bijvoet Center for Biomolecular Research, Utrecht University, The Netherlands.
Curr Biol. 1997 Oct 1;7(10):739-46. doi: 10.1016/s0960-9822(06)00332-0.
Integrase mediates a crucial step in the life cycle of the human immunodeficiency virus (HIV). The enzyme cleaves the viral DNA ends in a sequence-dependent manner and couples the newly generated hydroxyl groups to phosphates in the target DNA. Three domains have been identified in HIV integrase: an amino-terminal domain, a central catalytic core and a carboxy-terminal DNA-binding domain. The amino-terminal region is the only domain with unknown structure thus far. This domain, which is known to bind zinc, contains a HHCC motif that is conserved in retroviral integrases. Although the exact function of this domain is unknown, it is required for cleavage and integration.
The three-dimensional structure of the amino-terminal domain of HIV-2 integrase has been determined using two-dimensional and three-dimensional nuclear magnetic resonance data. We obtained 20 final structures, calculated using 693 nuclear Overhauser effects, which display a backbone root-mean square deviation versus the average of 0.25 A for the well defined region. The structure consists of three alpha helices and a helical turn. The zinc is coordinated with His 12 via the N epsilon 2 atom, with His16 via the N delta 1 atom and with the sulfur atoms of Cys40 and Cys43. The alpha helices form a three-helix bundle that is stabilized by this zinc-binding unit. The helical arrangement is similar to that found in the DNA-binding domains of the trp repressor, the prd paired domain and Tc3A transposase.
The amino-terminal domain of HIV-2 integrase has a remarkable hybrid structure combining features of a three-helix bundle fold with a zinc-binding HHCC motif. This structure shows no similarity with any of the known zinc-finger structures. The strictly conserved residues of the HHCC motif of retroviral integrases are involved in metal coordination, whereas many other well conserved hydrophobic residues are part of the protein core.
整合酶在人类免疫缺陷病毒（HIV）的生命周期中介导关键步骤。该酶以序列依赖的方式切割病毒DNA末端，并将新生成的羟基与靶DNA中的磷酸基团连接。HIV整合酶已鉴定出三个结构域：氨基末端结构域、中央催化核心和羧基末端DNA结合结构域。氨基末端区域是迄今为止唯一结构未知的结构域。该结构域已知与锌结合，包含在逆转录病毒整合酶中保守的HHCC基序。尽管该结构域的确切功能尚不清楚，但切割和整合过程需要它。
利用二维和三维核磁共振数据确定了HIV-2整合酶氨基末端结构域的三维结构。我们获得了20个最终结构，使用693个核Overhauser效应计算得出，在定义明确的区域，其主链相对于平均值的均方根偏差为0.25 Å。该结构由三个α螺旋和一个螺旋转角组成。锌通过Nε2原子与His 12配位，通过Nδ1原子与His16配位，并与Cys40和Cys43的硫原子配位。α螺旋形成一个三螺旋束，由这个锌结合单元稳定。这种螺旋排列与色氨酸阻遏物、prd配对结构域和Tc3A转座酶的DNA结合结构域中的排列相似。
HIV-2整合酶的氨基末端结构域具有显著的混合结构，结合了三螺旋束折叠和锌结合HHCC基序的特征。该结构与任何已知的锌指结构均无相似性。逆转录病毒整合酶HHCC基序中严格保守的残基参与金属配位，而许多其他保守的疏水残基是蛋白质核心的一部分。
