SOUL in mouse eyes is a new hexameric heme-binding protein with characteristic optical absorption, resonance Raman spectral, and heme-binding properties.
SOUL in mouse eyes is a new hexameric heme-binding protein with characteristic optical absorption, resonance Raman spectral, and heme-binding properties.
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DOI：
10.1021/bi048742i
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发表时间：
2004-10
期刊：
影响因子：
2.9
通讯作者：
E. Sato;I. Sagami;T. Uchida;Akira Sato;T. Kitagawa;J. Igarashi;Toru Shimizu
中科院分区：
文献类型：
--
作者：
E. Sato;I. Sagami;T. Uchida;Akira Sato;T. Kitagawa;J. Igarashi;Toru Shimizu
SOUL在视网膜和松果体中特异性表达，并与p22 HBP（一种在许多组织中普遍表达的血红素蛋白）显示出超过40%的序列同源性。SOUL在没有血红素的情况下从大肠杆菌表达系统中纯化为二聚体，但在血红素结合时显示六聚体结构。血红素结合的SOUL显示典型的6-坐标低自旋血红素蛋白质的光学吸收和共振拉曼光谱，每个单体单元的Fe（III）和Fe（II）络合物的一个血红素。光谱数据还表明，铁（III）血红素络合物的轴向配体之一是他。His 42（SOUL的唯一His）突变为Ala导致血红素结合丧失，证实该残基是SOUL的轴向配体。根据结合和解离速率常数，血红素对SOUL的K（d）值估计为4.8 × 10（-9）M，表明具有高结合亲和力。另一方面，p22 HBP是以每个亚基含有一个血红素的单体形式获得的，K（d）值为2.1 × 10（-11）M。血红素结合p22 HBP的光谱与SOUL的光谱不同，但与血红素结合牛血清白蛋白的光谱相似，其中血红素结合到疏水腔中，没有特定的轴向配体配位。因此，血红素结合特性和协调结构的SOUL是不同于那些p22 HBP，尽管高序列同源性。新的血红素结合蛋白，SOUL的生理作用，在本报告中进一步讨论。
SOUL is specifically expressed in the retina and pineal gland and displays more than 40% sequence homology with p22HBP, a heme protein ubiquitously expressed in numerous tissues. SOUL was purified as a dimer in the absence of heme from the Escherichia coli expression system but displayed a hexameric structure upon heme binding. Heme-bound SOUL displayed optical absorption and resonance Raman spectra typical of 6-coordinate low-spin heme protein, with one heme per monomeric unit for both the Fe(III) and Fe(II) complexes. Spectral data additionally suggest that one of the axial ligands of the Fe(III) heme complex is His. Mutation of His42 (the only His of SOUL) to Ala resulted in loss of heme binding, confirming that this residue is an axial ligand of SOUL. The K(d) value of heme for SOUL was estimated as 4.8 x 10(-9) M from the association and dissociation rate constants, suggesting high binding affinity. On the other hand, p22HBP was obtained as a monomer containing one heme per subunit, with a K(d) value of 2.1 x 10(-11) M. Spectra of heme-bound p22HBP were different from those of SOUL but similar to those of heme-bound bovine serum albumin in which heme bound to a hydrophobic cavity with no specific axial ligand coordination. Therefore, the heme-binding properties and coordination structure of SOUL are distinct from those of p22HBP, despite high sequence homology. The physiological role of the new heme-binding protein, SOUL, is further discussed in this report.