N-terminal acetylation and protonation of individual hemoglobin subunits: Position-dependent effects on tetramer strength and cooperativity
N-terminal acetylation and protonation of individual hemoglobin subunits: Position-dependent effects on tetramer strength and cooperativity
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DOI：
10.1110/ps.041267405
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发表时间：
2005-06-01
期刊：
影响因子：
8
通讯作者：
Manning, JM
中科院分区：
文献类型：
--
作者：
Ashiuchi, M;Yagami, T;Manning, JM
在成人血红蛋白的α-或β-亚基的N-末端存在丙氨酸（Ala）或乙酰丝氨酸（AcSer）而不是正常的瓦尔残基，赋予该蛋白一些新的和意想不到的特征。质谱分析证实这些取代是正确的，并且它们是唯一的取代。圆二色谱研究表明没有全球蛋白质构象的变化，等电聚焦显示不存在杂质。在配体血红蛋白的α-亚基的N-末端存在Ala导致碱性显著增加（增加的pK（a）值）和在变构四聚体-二聚体界面处亚基相互作用强度的降低。O-2结合的协同性也降低。在β亚基的N-末端替换Ala Lit既不产生这些效应。在任一亚基的N末端中的Ser取代导致其完全乙酰化（在表达期间）和四聚体-二聚体变构界面强度的大幅降低。当Ala或AcSer存在于α-亚基的N末端时，作为pH的函数的四聚体二聚体缔合/解离常数的图的斜率降低60%。这表明，由于网络的相互作用涉及的N和C末端的a-亚基是不太广泛的比β-亚基在配位的人血红蛋白破坏有可能有一个深刻的影响血红蛋白功能，如增加碱性，四聚体强度的影响，和协同性。
The presence of alanine (Ala) or acetyl serine (AcSer) instead of the normal Val residues at the N-terminals of either the alpha- or the beta-subunits of human adult hemoglobin confers some novel and unexpected features on the protein. Mass spectrometric analysis confirmed that these substitutions were correct and that they were the only ones. Circular dichroism studies indicated no global protein conformational changes, and isoelectric focusing showed the absence of impurities. The presence of Ala at the N-terminals of the alpha-subunits of liganded hemoglobin results in a significantly increased basicity (increased pK(a) values) and a reduction in the strength of subunit interactions at the allosteric tetramer-dimer interface. Cooperativity in O-2 binding is also decreased. Substitution of Ala Lit the N-terminals of the beta-subunits gives neither of these effects. The substitution of Ser in the N terminus of either Subunit leads to its complete acetylation (during expression) and a large decrease in the strength of the tetramer-dimer allosteric interface. When either Ala or AcSer is present at the N terminus of the alpha-subuint, the slope of the plot of the tetramer dimer association/dissociation constant as a function of pH is decreased by 60%. It is suggested that since the network of interactions involving the N and C termini of the a-subunits is less extensive than that of the beta-subunits in liganded human hemoglobin disruptions there are likely to have a profound effect on hemoglobin function Such as the increased basicity, the effects on tetramer strength, and on cooperativity.