The crystal structure of nitrophorin 4 at 1.5 Å resolution:: transport of nitric oxide by a lipocalin-based heme protein
The crystal structure of nitrophorin 4 at 1.5 Å resolution:: transport of nitric oxide by a lipocalin-based heme protein
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DOI：
10.1016/s0969-2126(98)00131-2
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发表时间：
1998-10-01
期刊：
影响因子：
5.7
通讯作者：
Montfort, WR
中科院分区：
文献类型：
--
作者：
Andersen, JF;Weichsel, A;Montfort, WR
背景资料：硝化蛋白是一氧化氮（NO）的转运蛋白，来自吸血昆虫的唾液，其作为血管扩张剂和抗血小板剂。Rhodnius prolixus是一种携带引起恰加斯病的锥虫的昆虫，在吸血期间释放四种装载NO的硝基蛋白，因此配体被释放到宿主的血流或周围组织中。组胺，由主机组织损伤后释放的信号分子，是紧密结合的nitrophorins，这可能有利于NO的释放，减少炎症在host.Results：重组nitrophorin 4（NP 4）在大肠杆菌中表达，重组血红素，并发现结合NO和组胺的方式类似的天然蛋白质。NP4的晶体结构揭示了一个脂质运载蛋白样的八链β桶，其中血红素插入桶的一端。His59连接血红素的近端位点，溶剂分子（NH4）连接远端位点，并且三个另外的溶剂分子占据远端口袋。埋在蛋白质内部的是Glu55和三个溶剂分子。与其他脂质运载蛋白的详细比较表明，NP4是密切相关的胆绿素结合蛋白从insect.Conclusions：nitrophorins有一个独特的血红素蛋白结构，是完全不同的球蛋白，唯一的其他血红素蛋白的目的是运输溶解气体。与最近描述的NP 1的结构相比，NP 4的结构是相当高的分辨率，证实了蛋白质内部的可电离基团的不寻常的位置，并澄清了远端口袋中的溶剂排列。它还提供了一个结构同源性的惊人例子，其中序列同源性是最小的。
Background: Nitrophorins are nitric oxide (NO) transport proteins from the saliva of blood-feeding insects, which act as vasodilators and anti-platelet agents. Rhodnius prolixus, an insect that carries the trypanosome that causes Chagas' disease, releases four NO-loaded nitrophorins during blood feeding, whereupon the ligand is released into the bloodstream or surrounding tissue of the host. Histamine, a signaling molecule released by the host upon tissue damage, is tightly bound by the nitrophorins; this may facilitate the release of NO and reduce inflammation in the host.Results: Recombinant nitrophorin 4 (NP4) was expressed in Escherichia coli, reconstituted with heme, and found to bind NO and histamine in a manner similar to that of the natural protein. The crystal structure of NP4 revealed a lipocalin-like eight-stranded beta barrel, with heme inserted into one end of the barrel. His59 ligates the proximal site on the heme, a solvent molecule (NH,) ligates the distal site, and three additional solvent molecules occupy the distal pocket. Buried in the protein interior are Glu55 and three solvent molecules. A detailed comparison with other lipocalins suggests that NP4 is closely related to the biliverdin-binding proteins from insects.Conclusions: The nitrophorins have a unique hemoprotein structure and are completely unlike the globins, the only other hemoproteins designed to transport dissolved gases. Compared with the recently described structure of NP1,the NP4 structure is considerably higher resolution, confirms the unusual placement of ionizable groups in the protein interior, and clarifies the solvent arrangement in the distal pocket. It also provides a striking example of structural homology where sequence homology is minimal.