Structural and energetic differences between insertions and substitutions in staphylococcal nuclease.
Structural and energetic differences between insertions and substitutions in staphylococcal nuclease.
复制标题
葡萄球菌核酸酶插入和取代之间的结构和能量差异。
DOI：
10.1002/prot.340130206
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发表时间：
1992
期刊：
影响因子：
2.9
通讯作者：
Shortle,D
中科院分区：
文献类型：
--
作者：
Sondek,J;Shortle,D
在之前的一项研究中，小蛋白葡萄球菌核酸酶被证明可以很容易地容纳单个丙氨酸和甘氨酸插入，其稳定性的平均损失与相同位点的取代（PROT）相当。29 - 305, 1990)。为了更充分地探索这种意想不到的对残基间距变化的适应性，在先前研究的10个位点上构建了2个双氨基酸插入（丙氨酰-甘氨酸，甘氨酸-甘氨酸）和3个具有不同侧链的单氨基酸插入（脯氨酸，亮氨酸和谷氨酰胺）。在其中8个位点上，插入残基的氨基酸侧链类型显著影响突变蛋白的稳定性。然而，在10个位点中的9个，发现双插入并不比单丙氨酸或甘氨酸插入更不稳定。相比之下，葡萄球菌核酸酶的双置换突变（用丙氨酸取代相邻的两个残基）没有表现出这种显著的非可加性。对单谷氨酰胺和单甘氨酸插入与丙酰-甘氨酸插入效果的比较表明，平均而言，将丙氨酸插入肽主链比将等效原子附加到甘氨酸插入的侧链上更不稳定。为了解释它们非常不同的能量效应，我们提出，与大多数取代不同，插入的残基必须引起多肽链的横向位移，迫使折叠构象远离野生型构象。由此产生的插入侧翼残基位置的强制性移动产生了大量的自由度，突变体结构可以围绕这些自由度放松。从多肽链可得到的许多可选择的包装和键合安排中，选择能量上最有利的。©1992 Wiley‐Liss, Inc。
In a previous study, the small protein staphylococcal nuclease was shown to readily accommodate single alanine and glycine insertions, with average losses in stability comparable to substitutions at the same sites (PROT. 7:29–305, 1990). To more fully explore this unexpected adaptability to changes in residue spacing, 2 double amino acid insertions (alanyl‐glycine, glycyl‐glycine) and 3 additional single amino acid insertions with dissimilar side chains (proline, leucine, and glutamine) were constructed at 10 of the sites previously studied. At 8 of these sites, the type of amino acid side chain on the inserted residue significantly influenced the stability of the mutant protein. However, at 9 of the 10 sites, the double insertions were found to be no more destabilizing than the single alanine or glycine insertions. In contrast, double substitution mutations of staphylococcal nuclease, which replace two adjacent residues with alanine, do not show this striking degree of non‐additivity. A comparison of the effects of single glutamine and single glycine insertions with alanyl‐glycine insertions indicates that insertion of alanine into the peptide backbone is, on average, less destabilizing than appending the equivalent atoms onto the side chain of a glycine insertion. To explain their very different energetic effects, we propose that, unlike most substitutions, the inserted residue(s) must induce lateral displacements of the polypeptide chain, forcing the folded conformation away from that of wild type. The resulting obligatory shifts in the positioning of residues flanking the insertion generate a large number of degrees of freedom around which the mutant structure can relax. From the many alternative packing and bonding arrangements thus made available to the polypeptide chain, the energetically most favorable is selected. © 1992 Wiley‐Liss, Inc.