Sugishima Masakazu, Oda Kenji, Ogura Takashi, Sakamoto Hiroshi, Noguchi Masato, Fukuyama Keiichi
Department of Medical Biochemistry, Kurume University School of Medicine, Japan.
Acta Crystallogr Sect F Struct Biol Cryst Commun. 2007 Jun 1;63(Pt 6):471-4. doi: 10.1107/S174430910702475X. Epub 2007 May 31.
Cyanide is a well known potent inhibitor of haem proteins, including haem oxygenase (HO). Generally, cyanide coordinates to the ferric haem iron with a linear binding geometry; the Fe-C-N angle ranges from 160 to 180 degrees . The Fe-C-N angle observed in the crystal structure of haem-HO bound to cyanide prepared at alkaline pH was 166 degrees . Here, it is reported that cyanide can bind to the haem iron in HO in a bent mode when the ternary complex is prepared at neutral pH; a crystal structure showed that the Fe-C-N angle was bent by 47 degrees . Unlike the ternary complex prepared at alkaline pH, in which the haem group, including the proximal ligand and the distal helix, was displaced upon cyanide binding, the positions of the haem group and the distal helix in the complex prepared at neutral pH were nearly identical to those in haem-HO. Cyanide that was bound to haem-HO with a bent geometry was readily photodissociated, whereas that bound with a linear geometry was not photodissociated. Thus, alternative cyanide-binding modes with linear and bent geometries exist in the crystalline state of haem-HO.
氰化物是一种众所周知的血红蛋白抑制剂，包括血红素加氧酶（HO）。一般来说，氰化物以线性结合几何结构与高铁血红素铁配位；铁 - 碳 - 氮角度范围为160至180度。在碱性pH条件下制备的与氰化物结合的血红素 - HO晶体结构中观察到的铁 - 碳 - 氮角度为166度。在此，据报道，当中性pH条件下制备三元复合物时，氰化物可以以弯曲模式与HO中的血红素铁结合；晶体结构表明铁 - 碳 - 氮角度弯曲了47度。与在碱性pH条件下制备的三元复合物不同，在碱性pH条件下制备的复合物中，包括近端配体和远端螺旋在内的血红素基团在氰化物结合时会发生位移，而在中性pH条件下制备的复合物中，血红素基团和远端螺旋的位置与血红素 - HO中的位置几乎相同。以弯曲几何结构与血红素 - HO结合的氰化物很容易光解离，而以线性几何结构结合的氰化物则不会光解离。因此，在血红素 - HO的晶体状态中存在具有线性和弯曲几何结构的氰化物结合模式。
