Allosteric regulation and temperature dependence of oxygen binding in human neuroglobin and cytoglobin - Molecular mechanisms and physiological significance
Allosteric regulation and temperature dependence of oxygen binding in human neuroglobin and cytoglobin - Molecular mechanisms and physiological significance
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DOI：
10.1074/jbc.m407126200
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发表时间：
2004-10-22
影响因子：
4.8
通讯作者：
Weber, RE
中科院分区：
文献类型：
--
作者：
Fago, A;Hundahl, C;Weber, RE
最近在脊椎动物中发现了两种新的珠蛋白，神经元中的神经珠蛋白和所有组织中的细胞珠蛋白，在没有气体配体的情况下，它们都表现出远端His（E7）的血红素六配位。与血红蛋白和肌红蛋白类似，神经红蛋白和细胞红蛋白被认为参与O-2的储存和传递，尽管它们的生理作用仍有待解决。在这里，我们报道了在接近生理条件下，在不同温度和pH范围内测量重组人神经球蛋白（NGB）和细胞球蛋白（CYGB）的O-2平衡。NGB同时表现出碱性和酸性玻尔效应（ph依赖的O-2亲和力）和温度依赖的氧化焓。对神经球蛋白突变体的O-2和CO结合平衡的研究强烈表明，结合的O-2通过与His（E7）的相互作用而稳定，并且该残基在赖氨酸存在时作为主要的玻尔基团发挥作用（E10）。通过4,4'-二硫代二吡啶滴定游离硫醇和质谱分析表明，在实验条件下，这种调节O-2亲和力的机制与形成内部二硫键无关，该键稳定了硫醇的还原形式。在CYGB中，O-2的结合是协同的，与所提出的二聚体结构一致。与肌红蛋白相似，但与NGB相反，O-2与CYGB的结合是ph无关的，在整个研究温度范围内都是放热的。我们的数据支持CYGB可能参与需要o -2的代谢过程的假设。相反，NGB中较低的O-2亲和力似乎与神经元内低O-2张力时线粒体O-2供应的生理作用不相容。
Two new globin proteins have recently been discovered in vertebrates, neuroglobin in neurons and cytoglobin in all tissues, both showing heme hexacoordination by the distal His(E7) in the absence of gaseous ligands. In analogy to hemoglobin and myoglobin, neuroglobin and cytoglobin are supposedly involved in O-2 storage and delivery, although their physiological role remains to be solved. Here we report O-2 equilibria of recombinant human neuroglobin (NGB) and cytoglobin (CYGB) measured under close to physiological conditions and at varying temperature and pH ranges. NGB shows both alkaline and acid Bohr effects (pH-dependent O-2 affinity) and temperature-dependent enthalpy of oxygenation. O-2 and CO binding equilibrium studies on neuroglobin mutants strongly suggest that the bound O-2 is stabilized by interactions with His(E7) and that this residue functions as a major Bohr group in the presence of Lys(E10). As shown by the titration of free thiols with 4,4'-dithiodipyridine and by mass spectrometry, this mechanism of modulating O-2 affinity is independent of formation of an internal disulfide bond under the experimental conditions used, which stabilize thiols in the reduced form. In CYGB, O-2 binding is cooperative, consistent with its proposed dimeric structure. Similar to myoglobin but in contrast to NGB, O-2 binding to CYGB is pH-independent and exothermic throughout the temperature range investigated. Our data support the hypothesis that CYGB may be involved in O-2-requiring metabolic processes. In contrast, the lower O-2 affinity in NGB does not appear compatible with a physiological role involving mitochondrial O-2 supply at the low O-2 tensions found within neurons.