HOW ALLOSTERIC EFFECTORS CAN BIND TO THE SAME PROTEIN RESIDUE AND PRODUCE OPPOSITE SHIFTS IN THE ALLOSTERIC EQUILIBRIUM
HOW ALLOSTERIC EFFECTORS CAN BIND TO THE SAME PROTEIN RESIDUE AND PRODUCE OPPOSITE SHIFTS IN THE ALLOSTERIC EQUILIBRIUM
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DOI：
10.1021/bi00046a007
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发表时间：
1995-11-21
期刊：
影响因子：
2.9
通讯作者：
POYART, C
中科院分区：
文献类型：
--
作者：
ABRAHAM, DJ;SAFO, MK;POYART, C
使用分子模拟软件（GRID）设计血红蛋白的单醛变构效应物，以与瓦尔1 α N-末端氮形成席夫碱加合物，并通过盐桥与相对亚基的Arg 141 α相互作用。如果没有设计的分子，则合成设计的分子。据设想，这些分子是醛酸，将产生高亲和力血红蛋白，具有作为类似于先前报道的其他醛酸的抗镰状剂的潜在兴趣。X-射线晶体学分析表明，醛酸确实结合作为建模从头在α亚基N-末端氮相关的对。然而，氧平衡曲线运行的解决方案，从T-（紧张）状态血红蛋白晶体的反应效应分子产生的低亲和力血红蛋白。变构平衡的变化与预期的相反。我们得出结论，观察到的变构平衡的变化是由于单醛芳环上的酸基团与相对亚基上的Arg 141 α的胍离子形成盐桥。这对T态结构增加了约束，使两个亚基横跨分子对称轴，使平衡进一步向T态移动。我们通过比较与相同的瓦尔1 α残基形成席夫碱相互作用但不跨二聚体亚基对称轴相互作用的醛来测试这一想法（在本研究中，一种新的醛没有酸基团，而其他醛已经确定了晶体结构），后一种醛将变构平衡向R-状态移动。提出了一个预测变构平衡转变方向的假设，并表明它不仅是分子结合的地方，而是它如何与蛋白质相互作用以稳定或破坏T-（紧张）变构状态。
Monoaldehyde allosteric effecters of hemoglobin were designed, using molecular modeling software (GRID), to form a Schiff base adduct with the Val 1 alpha N-terminal nitrogens and interact via a salt bridge with Arg 141 alpha of the opposite subunit. The designed molecules were synthesized if not available. It was envisioned that the molecules, which are aldehyde acids, would produce a high-affinity hemoglobin with potential interest as antisickling agents similar to other aldehyde acids reported earlier. X-ray crystallographic analysis indicated that the aldehyde acids did bind as modeled de novo in symmetry-related pairs to the alpha subunit N-terminal nitrogens. However, oxygen equilibrium curves run on solutions obtained from T- (tense) state hemoglobin crystals of reacted effector molecules produced low-affinity hemoglobins. The shift in the allosteric equilibrium was opposite to that expected, We concluded that the observed shift in allosteric equilibrium was due to the acid, group on the monoaldehyde aromatic ring that forms a salt bridge with the guanidinium ion of Arg 141 alpha on the opposite subunit. This added constraint to the T-state structure that ties two subunits across the molecular symmetry axis shifts the equilibrium further toward the T-state. We tested this idea by comparing aldehydes that form Schiff base interactions with the same Val 1 alpha residues but do not interact across the dimer subunit symmetry axis (a new one in this study with no acid group and others that have had determined crystal structures), The latter aldehydes shift the allosteric equilibrium toward the R-state. A hypothesis to predict the direction in shift of the allosteric equilibrium is made and indicates that it is not exclusively where the molecule binds but how it interacts with the protein to stabilize or destabilize the T- (tense) allosteric state.