A hydrogen-bonding network formed by the B10-E7-E11 residues of a truncated hemoglobin from Tetrahymena pyriformis is critical for stability of bound oxygen and nitric oxide detoxification
A hydrogen-bonding network formed by the B10-E7-E11 residues of a truncated hemoglobin from Tetrahymena pyriformis is critical for stability of bound oxygen and nitric oxide detoxification
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DOI：
10.1007/s00775-011-0761-3
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发表时间：
2011-04-01
影响因子：
3
通讯作者：
Matsuoka, Ariki
中科院分区：
文献类型：
--
作者：
Igarashi, Jotaro;Kobayashi, Kazuo;Matsuoka, Ariki
截短型血红蛋白(TrHbs)广泛分布于细菌和单细胞真核生物体内，在氧转运和一氧化氮解毒中发挥重要作用。已知trHb存在于四膜虫类的纤毛虫中，但trHb的结构和功能尚不清楚。为了研究trHb在结合氧和蛋白质结构稳定性方面的作用，我们测定了梨形四膜虫trHb的氧结合动力学，并测定了该蛋白质的晶体结构。梨形毛虫trHb的O-2缔合和解离速率常数分别为5.5亩M-1 S(-1)和0.18 S(-1)。自氧化速率常数为3.8×10~(-3)h~(-1)。这些值与结核分枝杆菌hBN的值相似。在1.73埃分辨率下测定了梨形毛虫trHb的Fe(II)-O-2络合物的三维结构。Tyr25(B10)和Gln46(E7)与血红素结合的O-2分子上存在氢键。Tyr25与末端的氧原子形成氢键，而Gln46与近端的氧原子形成氢键。此外，Tyr25与Gln46和Gln50(E11)残基形成氢键。Tyr25、Gln46和Gln50的突变增加了O-2解离和自氧化速率常数。梨形毛滴虫trHb的Fe(II)-O-2络合物与一氧化氮形成结晶态的Fe(III)-H2O络合物。这表明梨形毛滴虫trHb在一氧化氮解毒中起作用。
Truncated hemoglobins (trHbs) are distributed from bacteria to unicellular eukaryotes and have roles in oxygen transport and nitric oxide detoxification. It is known that trHbs exist in ciliates of the Tetrahymena group, but trHb structure and function remain poorly understood. To investigate trHb function with respect to stability of bound oxygen and protein structure, we measured the oxygen binding kinetics of Tetrahymena pyriformis trHb, and determined the crystal structure of the protein. The O-2 association and dissociation rate constants of T. pyriformis trHb were 5.5 mu M-1 s(-1) and 0.18 s(-1), respectively. The autooxidation rate constant was 3.8 x 10(-3) h(-1). These values are similar to those of HbN from Mycobacterium tuberculosis. The three-dimensional structure of an Fe(II)-O-2 complex of T. pyriformis trHb was determined at 1.73-angstrom resolution. Tyr25 (B10) and Gln46 (E7) were hydrogen-bonded to a heme-bound O-2 molecule. Tyr25 donated a hydrogen bond to the terminal oxygen atom, whereas Gln46 hydrogen-bonded to the proximal oxygen atom. Furthermore, Tyr25 was hydrogen-bonded to the Gln46 and Gln50 (E11) residues. Mutations at Tyr25, Gln46, and Gln50 increased the O-2 dissociation and autooxidation rate constants. An Fe(III)-H2O complex of T. pyriformis trHb was formed following reaction of the Fe(II)-O-2 complex of T. pyriformis trHb, in a crystal state, with nitric oxide. This suggests that T. pyriformis trHb functions in nitric oxide detoxification.