HIGH-RESOLUTION CRYSTAL-STRUCTURES OF DISTAL HISTIDINE MUTANTS OF SPERM WHALE MYOGLOBIN
HIGH-RESOLUTION CRYSTAL-STRUCTURES OF DISTAL HISTIDINE MUTANTS OF SPERM WHALE MYOGLOBIN
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DOI：
10.1006/jmbi.1993.1569
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发表时间：
1993-11-05
影响因子：
5.6
通讯作者：
PHILLIPS, GN
中科院分区：
文献类型：
--
作者：
QUILLIN, ML;ARDUINI, RM;PHILLIPS, GN
抹香鲸肌红蛋白的高度保守的远端组氨酸残基（His 64）调节配体的亲和力。为了充分表征突变残基64的影响，我们已经确定了Gly 64，Val 64，Leu 64，Thr 64和Gln 64突变体的几种配体形式的高分辨率晶体结构。在残基64处具有疏水取代的Metmyoglobins（Val 64和Leu 64）在第六配位位置处缺乏水分子，而在该位置处具有极性氨基酸残基的Metmyoglobins（野生型和Gln 64）保留共价结合的水分子。在Thr 64突变体中，结合水位置仅部分被占据。相比之下，突变的远端组氨酸残基甘氨酸不会导致损失的配位水分子，因为从咪唑侧链的氢键被取代的一个从一个有序的溶剂水分子。在水结构的差异周围的远端口袋也是显而易见的脱氧肌红蛋白突变体的结构。与野生型脱氧肌红蛋白中组氨酸64的Nε原子氢键结合的水分子在任何已确定的64位突变体结构中均未发现。比较野生型、Gly 64、Leu 64和Gln 64肌红蛋白P6晶型的一碳氧结构表明，Fe-C-O复合物的构象几乎是线性的，并且与64位氨基酸残基的身份无关。然而，CO结合对残基64的构象的影响是惊人的。脱氧和碳一氧基结构的叠加揭示了野生型和Gln 64肌红蛋白中残基64侧链的显著位移，但Leu 64突变体中没有位移。这些详细的结构研究提供了关键的见解配体结合和肌红蛋白的歧视机制。
The highly conserved distal histidine residue (His64) of sperm whale myoglobin modulates the affinity of ligands. In an effort to fully characterize the effects of mutating residue 64, we have determined the high-resolution crystal structures of the Gly64, Val64, Leu64, Thr64 and Gln64 mutants in several liganded forms. Metmyoglobins with hydrophobic substitutions at residue 64 (Val64 and Leu64) lack a water molecule at the sixth coordination position, while those with polar amine acid residues at this position (wild-type and Gln64) retain a covalently bound water molecule. In the Thr64 mutant, the bound water position is only partially occupied. In contrast, mutating the distal histidine residue to glycine does not cause loss of the coordinated water molecule, because the hydrogen bond from the imidazole side-chain is replaced by one from a well-ordered solvent water molecule. Differences in water structure around the distal pocket are apparent also in the structures of deoxymyoglobin mutants. The water molecule that is hydrogen-bonded to the Nε atom of histidine 64 in wild-type deoxymyoglobin is not found in any of the position 64 mutant structures that were determined. Comparison of the carbonmonoxy structures of wild-type, Gly64, Leu64 and Gln64 myoglobins in theP6 crystal form shows that the conformation of the Fe-C-O complex is nearly linear and is independent of the identity of the amino acid residue at position 64. However, the effect of CO binding on the conformation of residue 64 is striking. Superposition of deoxy and carbonmonoxy structures reveals significant displacements of the residue 64 side-chain in the wild-type and Gln64 myoglobins, but no displacement in the Leu64 mutant. These detailed structural studies provide key insights into the mechanisms of ligand binding and discrimination in myoglobin.