Pesce A, Dewilde S, Kiger L, Milani M, Ascenzi P, Marden M C, Van Hauwaert M L, Vanfleteren J, Moens L, Bolognesi M
Department of Physics-INFM, Advanced Biotechnology Centre, University of Genova, Largo Rosanna Benzi, 10, Genova, I-16132, Italy.
J Mol Biol. 2001 Jun 22;309(5):1153-64. doi: 10.1006/jmbi.2001.4731.
Monomeric hemoglobin from the trematode Paramphistomum epiclitum displays very high oxygen affinity (P(50)<0.001 mm Hg) and an unusual heme distal site containing tyrosyl residues at the B10 and E7 positions. The crystal structure of aquo-met P. epiclitum hemoglobin, solved at 1.17 A resolution via multiwavelength anomalous dispersion techniques (R-factor=0.121), shows that the heme distal site pocket residue TyrB10 is engaged in hydrogen bonding to the iron-bound ligand. By contrast, residue TyrE7 is unexpectedly locked next to the CD globin region, in a conformation unsuitable for heme-bound ligand stabilisation. Such structural organization of the E7 distal residue differs strikingly from that observed in the nematode Ascaris suum hemoglobin (bearing TyrB10 and GlnE7 residues), which also displays very high oxygen affinity. The oxygenation and carbonylation parameters of wild-type P. epiclitum Hb as well as of single- and double-site mutants, with residue substitutions at positions B10, E7 and E11, have been determined and are discussed here in the light of the protein atomic resolution crystal structure.
来自吸虫类后睾吸虫的单体血红蛋白表现出非常高的氧亲和力（P(50)<0.001 mmHg），并且在B10和E7位置含有酪氨酸残基的异常血红素远端位点。通过多波长反常色散技术（R因子 = 0.121）以1.17 Å分辨率解析的水合高铁后睾吸虫血红蛋白的晶体结构表明，血红素远端位点口袋残基TyrB10与铁结合配体形成氢键。相比之下，残基TyrE7意外地锁定在CD球蛋白区域旁边，处于不适合血红素结合配体稳定化的构象。E7远端残基的这种结构组织与在线虫猪蛔虫血红蛋白（带有TyrB10和GlnE7残基）中观察到的情况显著不同，后者也表现出非常高的氧亲和力。已经确定了野生型后睾吸虫血红蛋白以及在B10、E7和E11位置进行残基替换的单位点和双位点突变体的氧合和羰基化参数，并根据蛋白质原子分辨率晶体结构在此进行了讨论。
