Vásquez G B, Ji X, Fronticelli C, Gilliland G L
Center for Advanced Research in Biotechnology of the University of Maryland Biotechnology Institute, and of the National Institute of Standards and Technology, 9600 Gudelsky Drive, Rockville, Maryland 20850, USA.
Acta Crystallogr D Biol Crystallogr. 1998 May 1;54(Pt 3):355-66. doi: 10.1107/s0907444997012250.
The three-dimensional structure and associated solvent of human carboxyhemoglobin at 2.2 A resolution are compared with other R-state and T-state human hemoglobin structures. The crystal form is isomorphous with that of the 2.7 A structure of carboxyhemoglobin reported earlier [Baldwin (1980). J. Mol. Biol. 136, 103-128], whose coordinates were used as a starting model, and with the 2.2 A structure described in an earlier report [Derewenda et al. (1990). J. Mol. Biol. 211, 515-519]. During the course of the refinement, a natural mutation of the alpha-subunit, A53S, was discovered that forms a new crystal contact through a bridging water molecule. The protein structure shows a significant difference between the alpha and beta heme geometries, with Fe-C-O angles of 125 and 162 degrees, respectively. The carboxyhemoglobin is compared with other fully ligated R-state human hemoglobins [Baldwin (1980). J. Mol. Biol. 136, 103-128; Shaanan (1983). J. Mol. Biol. 195, 419-422] with the R2-state hemoglobin [Silva et al. (1992). J. Biol. Chem. 267, 17248-17256] and with T-state deoxyhemoglobin [Fronticelli et al. (1994). J. Biol. Chem. 269, 23965-23969]. The structure is similar to the earlier reported R-state structures, but there are differences in many side-chain conformations, the associated water structure and the presence and the position of a phosphate ion. The quaternary changes between the R-state carboxyhemoglobin and the R2-state and T-state structures are in general consistent with those reported in the earlier structures. The location of 238 water molecules and a phosphate ion in the carboxyhemoglobin structure allows the first comparison of the solvent structures of the R-state and T-state structures. Distinctive hydration patterns for each of the quaternary structures are observed, but a number of conserved water molecule binding sites are found that are independent of the conformational state of the protein.
将分辨率为2.2 Å的人羧基血红蛋白的三维结构及相关溶剂与其他R态和T态人血红蛋白结构进行了比较。该晶体形式与先前报道的羧基血红蛋白2.7 Å结构[鲍德温（1980年）。《分子生物学杂志》136卷，第103 - 128页]同晶型，其坐标用作起始模型，也与先前一篇报道中描述的2.2 Å结构[德雷温达等人（1990年）。《分子生物学杂志》211卷，第515 - 519页]同晶型。在精修过程中，发现α亚基的一个自然突变A53S，它通过一个桥连水分子形成了一种新的晶体接触。蛋白质结构显示α和β血红素几何形状存在显著差异，Fe - C - O角分别为125度和162度。将羧基血红蛋白与其他完全结合的R态人血红蛋白[鲍德温（1980年）。《分子生物学杂志》136卷，第103 - 128页；沙南（1983年）。《分子生物学杂志》195卷，第419 - 422页]、R2态血红蛋白[席尔瓦等人（1992年）。《生物化学杂志》267卷，第17248 - 17256页]以及T态脱氧血红蛋白[弗龙蒂切利等人（1994年）。《生物化学杂志》269卷，第23965 - 23969页]进行了比较。该结构与先前报道的R态结构相似，但在许多侧链构象、相关水结构以及磷酸根离子的存在和位置方面存在差异。R态羧基血红蛋白与R2态和T态结构之间的四级结构变化总体上与先前结构中报道的一致。羧基血红蛋白结构中238个水分子和一个磷酸根离子的位置使得能够首次比较R态和T态结构的溶剂结构。观察到每种四级结构都有独特的水化模式，但发现了一些与蛋白质构象状态无关的保守水分子结合位点。
