Rajabzadeh Masoumeh, Kao Jeff, Frieden Carl
Ciphergen Biosystems, Inc., Fremont, California 94555, USA.
Biochemistry. 2003 Oct 28;42(42):12192-9. doi: 10.1021/bi0301688.
The intestinal fatty acid binding protein (IFABP) is a small (15 kDa) protein consisting mostly of 10 antiparallel beta-strands (A-J) and a small helical region that serves as a portal for the ligand. Two beta-sheet structures (strands A-E and F-J) surround a cavity into which the ligand binds. In this work, we investigated how changes in the side chains of specific residues are propagated through the structure. To determine what these changes were and how they relate to changes in stability, (15)N chemical shift perturbations were measured and compared to those of the wild-type protein. Seven mutations, five of which change either valine or leucine to glycine, have been examined. All these mutants were less stable than wild-type IFABP, suggesting some structural changes. For five of the mutants, the data suggest that destabilization of a small region of the protein propagates throughout the structure, resulting in an overall decrease in stability. In two (Leu38Gly and Leu89Gly), the loss of cooperativity in the equilibrium denaturation curves suggests that the destabilization of one region may not be transmitted to other regions in a cooperative manner. It is shown that the effect of mutating hydrophobic residues is much greater than that observed upon mutation of a solvent-exposed polar residue.
肠脂肪酸结合蛋白（IFABP）是一种小蛋白（15 kDa），主要由10条反平行β链（A - J）和一个作为配体通道的小螺旋区域组成。两个β片层结构（链A - E和F - J）围绕着一个配体结合的腔。在这项工作中，我们研究了特定残基侧链的变化是如何在结构中传播的。为了确定这些变化是什么以及它们与稳定性变化的关系，测量了（15）N化学位移扰动并与野生型蛋白的进行比较。已经研究了7个突变，其中5个将缬氨酸或亮氨酸变为甘氨酸。所有这些突变体都比野生型IFABP稳定性低，表明存在一些结构变化。对于其中5个突变体，数据表明蛋白质一个小区域的不稳定在整个结构中传播，导致稳定性总体下降。在两个突变体（Leu38Gly和Leu89Gly）中，平衡变性曲线中协同性的丧失表明一个区域的不稳定可能不会以协同方式传递到其他区域。结果表明，疏水残基突变的影响远大于溶剂暴露的极性残基突变时观察到的影响。
