Rashid A K, Van Hauwaert M L, Haque M, Siddiqi A H, Lasters I, De Maeyer M, Griffon N, Marden M C, Dewilde S, Clauwaert J, Vinogradov S N, Moens L
Department of Biochemistry, University of Antwerp (UIA), B-2610 Wilrijk, Belgium.
J Biol Chem. 1997 Jan 31;272(5):2992-9. doi: 10.1074/jbc.272.5.2992.
The myoglobins of two trematodes, Paramphistomum epiclitum and Isoparorchis hypselobagri, were isolated to homogeneity. The native molecules are monomeric with Mr 16,000-17,000 and pI 6.5-7.5. In each species, at least four different globin isoforms occur. Primary structure was determined at the protein level. The globin chains contain 147 amino acid residues. Although major determinants of the globin fold are conserved, characteristic substitutions are present. A Tyr residue occurs at the helical positions B10 and E7 (distal position). This is confirmed by NMR measurements (Zhang, W., Rashid, K. A., Haque, M., Siddiqi, A. H., Vinogradov, S. N., Moens, L. & La Mar, G. N. (1997) J. Biol. Chem. 272, 3000-3006). A distal Tyr normally provokes oxidation of the iron atom and the inability to bind oxygen, whereas a Tyr-B10 is indicative for a high oxygen affinity. In contrast, trematode myoglobins are functional molecules with a high oxygen affinity. Molecular modeling predicts two possible positions for the aromatic ring of Tyr-E7: one being outside the heme pocket making it freely accessible to the ligand and one within the heme pocket potentially able to form a second hydrogen bond with the iron-bound oxygen. A hydrogen bond between Tyr-B10 and the bound oxygen as in the Ascaris hemoglobin is predicted as well. The predicted structure may explain the high oxygen affinity of the trematode myoglobins.
两种吸虫，即中型双腔吸虫（Paramphistomum epiclitum）和高囊异双盘吸虫（Isoparorchis hypselobagri）的肌红蛋白被分离至均一状态。天然分子为单体，相对分子质量为16,000 - 17,000，等电点为6.5 - 7.5。在每个物种中，至少存在四种不同的球蛋白同工型。在蛋白质水平上确定了一级结构。球蛋白链包含147个氨基酸残基。尽管球蛋白折叠的主要决定因素是保守的，但存在特征性取代。一个酪氨酸（Tyr）残基出现在螺旋位置B10和E7（远端位置）。这通过核磁共振测量得到了证实（Zhang, W., Rashid, K. A., Haque, M., Siddiqi, A. H., Vinogradov, S. N., Moens, L. & La Mar, G. N. (1997) J. Biol. Chem. 272, 3000 - 3006）。一个远端酪氨酸通常会引发铁原子的氧化以及无法结合氧气，而酪氨酸 - B10则表明具有高氧亲和力。相比之下，吸虫肌红蛋白是具有高氧亲和力的功能性分子。分子建模预测了酪氨酸 - E7芳香环的两个可能位置：一个在血红素口袋外部，使其可自由接触配体，另一个在血红素口袋内，可能能够与铁结合的氧气形成第二个氢键。还预测了像蛔虫血红蛋白那样酪氨酸 - B10与结合氧气之间存在氢键。预测的结构可能解释了吸虫肌红蛋白的高氧亲和力。
