Department of Organic Chemistry and Biochemistry, University of Naples Federico II, 80126 Naples, Italy.
Biochimie. 2012 Apr;94(4):953-60. doi: 10.1016/j.biochi.2011.12.013. Epub 2012 Jan 11.
All tetrameric hemoglobins from Antarctic fish, including that from Trematomus bernacchii, HbTb form in the ferric state, promptly and distinctively from all the other tetrameric hemoglobins, a mixture of aquo-met at the α subunits and bis-histidyl adduct (hemichrome) at the β subunits. The role of the tertiary and quaternary structure in the hemichrome formation is unknown. Here we report the cloning, expression, purification, spectroscopic and computational characterization of the β-chain of HbTb (β-HbTb). Similarly to the human β-chains, β-HbTb self-assembles to form the homotetramer β(4)-HbTb; however, the latter quantitatively forms reversible ferric and ferrous bis-histidyl adducts, which are only partially present in the human tetramer (β(4)-HbA). A molecular dynamics study of the isolated β subunit of the two Hbs indicates that the ability to form hemichrome is an intrinsic feature of the chain; moreover, the greater propensity of β-HbTb to form the bis-histidyl adduct is probably linked to the higher flexibility of the CD loop region. On the bases of these experimental and computational results on the isolated chain, the influence of the quaternary structure on the stability of the endogenous ferrous and ferric hexa-coordination is also discussed.
所有来自南极鱼类的四聚血红蛋白，包括 Trematomus bernacchii 的血红蛋白 HbTb，在铁态下迅速而明显地与所有其他四聚血红蛋白形成水合-甲（aquomet）-α亚基和双组氨酸加合物（hemichrome）-β亚基混合物。三级和四级结构在形成亚铁血红素中的作用尚不清楚。在这里，我们报告了 HbTb 的β链（β-HbTb）的克隆、表达、纯化、光谱和计算特性。与人类的β链类似，β-HbTb 自身组装形成同四聚体β(4)-HbTb；然而，后者定量形成可逆的铁和亚铁双组氨酸加合物，而这些加合物仅部分存在于人类四聚体（β(4)-HbA）中。对两种 Hbs 的分离β亚基的分子动力学研究表明，形成亚铁血红素的能力是链的固有特征；此外，β-HbTb 形成双组氨酸加合物的倾向性更高可能与 CD 环区域的更高灵活性有关。基于对分离链的这些实验和计算结果，还讨论了四级结构对内源性亚铁和铁六配位稳定性的影响。
