Sawai Hitomi, Makino Masatomo, Mizutani Yasuhisa, Ohta Takehiro, Sugimoto Hiroshi, Uno Tadayuki, Kawada Norifumi, Yoshizato Katsutoshi, Kitagawa Teizo, Shiro Yoshitsugu
Department of Life Science, Graduate School of Science, Himeji Institute of Technology/University of Hyogo, 3-2-1 Kouto, Kamigori-cho, Ako, Hyogo 678-1297, Japan.
Biochemistry. 2005 Oct 11;44(40):13257-65. doi: 10.1021/bi050997o.
Cytoglobin (Cgb) and neuroglobin (Ngb) are the first examples of hexacoordinated globins from humans and other vertebrates in which a histidine (His) residue at the sixth position of the heme iron is an endogenous ligand in both the ferric and ferrous forms. Static and time-resolved resonance Raman and FT-IR spectroscopic techniques were applied in examining the structures in the heme environment of these globins. Picosecond time-resolved resonance Raman (ps-TR3) spectroscopy of transient five-coordinate heme species produced by the photolysis of carbon monoxide (CO) adducts of Cgb and Ngb showed Fe-His stretching (nu(Fe-His)) bands at 229 and 221 cm(-1), respectively. No time-dependent shift in the nu(Fe-His) band of Cgb and Ngb was detected in the 20-1000 ps time domain, in contrast to the case of myoglobin (Mb). These spectroscopic data, combined with previously reported crystallographic data, suggest that the structure of the heme pocket in Cgb and Ngb is altered upon CO binding in a manner different from that of Mb and that the scales of the structural alteration are different for Cgb and Ngb. The structural property of the heme distal side of the ligand-bound forms was investigated by observing the sets of (nu(Fe-CO), nu(C-O), delta(Fe-C-O)) and (nu(Fe-NO), nu(N-O), delta(Fe-N-O)) for the CO and nitric oxide (NO) complexes of Cgb and Ngb. A comparison of the spectra of some distal mutants of Cgb (H81A, H81V, R84A, R84K, and R84T) and Ngb (H64A, H64V, K67A, K67R, and K67T) showed that the CO adducts of Cgb and Ngb contained three conformers and that the distal His (His81 in Cgb and His64 in Ngb) mainly contributes to the interconversion of the conformers. These structural characteristics of Cgb and Ngb are discussed in relation to their ligand binding and physiological properties.
细胞珠蛋白（Cgb）和神经珠蛋白（Ngb）是人类及其他脊椎动物中六配位珠蛋白的首个实例，其中血红素铁第六位的组氨酸（His）残基在高铁和亚铁形式中均为内源性配体。静态和时间分辨共振拉曼光谱以及傅里叶变换红外光谱技术被用于研究这些珠蛋白血红素环境中的结构。对Cgb和Ngb的一氧化碳（CO）加合物进行光解产生的瞬态五配位血红素物种的皮秒时间分辨共振拉曼（ps-TR3）光谱显示，Fe-His伸缩振动（ν(Fe-His)）带分别位于229和221 cm⁻¹处。与肌红蛋白（Mb）的情况不同，在20 - 1000 ps时域内未检测到Cgb和Ngb的ν(Fe-His)带随时间的位移。这些光谱数据与先前报道的晶体学数据相结合，表明Cgb和Ngb中血红素口袋的结构在CO结合时以不同于Mb的方式发生改变，并且Cgb和Ngb结构改变的程度不同。通过观察Cgb和Ngb的CO和一氧化氮（NO）配合物的（ν(Fe-CO)、ν(C-O)、δ(Fe-C-O)）和（ν(Fe-NO)、ν(N-O)、δ(Fe-N-O)）集合，研究了配体结合形式血红素远端的结构性质。对Cgb（H81A、H81V、R84A、R84K和R84T）和Ngb（H64A、H64V、K67A、K67R和K67T）的一些远端突变体的光谱比较表明，Cgb和Ngb的CO加合物包含三种构象，并且远端His（Cgb中的His81和Ngb中的His64）主要促成构象的相互转化。结合它们的配体结合和生理特性对Cgb和Ngb的这些结构特征进行了讨论。
