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首页> 外文期刊>Biochemistry >Ligand-linked changes at the subunit interfaces in Scapharca hemoglobins probed through the sulfhydryl infrared absorption.
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Ligand-linked changes at the subunit interfaces in Scapharca hemoglobins probed through the sulfhydryl infrared absorption.

机译：通过巯基红外吸收探测到的Scapharca血红蛋白亚基界面处的配体连接变化。

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摘要

FTIR spectra of native Scapharca homodimeric hemoglobin (HbI) and of the Phe97-->Ile mutant have been measured in the region 2400-2700 cm(-1) where the absorption of the sulfhydryl groups can be observed. In native HbI, the two Cys92 residues give rise to a relatively intense band centered at 2559 cm(-1) that is shifted to 2568 cm(-1) and strongly quenched upon ligand binding. In the Phe97-->Leu mutant, such ligand-linked changes are not observed and the strong peak at around 2560 cm(-1) persists in the liganded derivatives. In native HbI, the observed changes have been attributed to the decrease in polarity of the interface due to the ligand-induced extrusion of the Phe97 phenyl ring from the heme pocket to the interface and the subsequent release of several water molecules that are clustered in the vicinity of Cys92. In contrast, in the Phe97-->Leu mutant, the Leu residue does not leave the heme pocket upon ligand binding and the interface is unaltered. The Cys92/S-H infrared band, therefore, represents a sensitive probe of the structural rearrangements that take place in the intersubunit interface upon ligand binding to HbI. The heterotetrameric Scapharca hemoglobin HbII contains, in addition to the Cys92 residues in the interfaces, two extra sulfhydryl groups per tetramer (Cys9 in the B chain) that are exposed to solvent in the A helix. The frequency of the Cys9/S-H stretching vibration occurs at 2582 cm(-1) in the unliganded and at 2586 cm(-1) in the liganded derivative, pointing to the involvement of the A helix in the ligand-linked polymerization characteristic of HbII.
机译：天然Scapharca同型二聚体血红蛋白（HbI）和Phe97-> Ile突变体的FTIR光谱已在2400-2700 cm（-1）的区域进行了测量，在该区域可以观察到巯基的吸收。在天然HbI中，两个Cys92残基产生一个相对强的条带，中心位于2559 cm（-1），移至2568 cm（-1），并在配体结合后强烈淬灭。在Phe97-> Leu突变体中，未观察到此类配体相关的变化，并且在2560 cm（-1）附近的强峰仍保留在配体衍生物中。在天然HbI中，观察到的变化归因于界面极性的降低，这是由于配体诱导的Phe97苯环从血红素囊袋到界面的挤出以及随后释放的一些水分子聚集成了界面。 Cys92附近。相反，在Phe97-> Leu突变体中，Leu残基在配体结合后不会离开血红素囊，并且界面未改变。因此，Cys92 / S-H红外波段代表在配体与HbI结合后在亚基间界面发生的结构重排的敏感探针。异四聚体Scapharca血红蛋白HbII除界面中的Cys92残基外，每个四聚体（B链中的Cys9）还含有两个额外的巯基，这些硫氢基暴露于A螺旋中的溶剂。 Cys9 / SH拉伸振动的频率发生在未配体的2582 cm（-1）和在配体的衍生物中的2586 cm（-1），表明A螺旋参与了HbII的配体连接聚合特性。

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