Bakkum Amber L, Hill R Blake
Department of Biochemistry, Medical College of Wisconsin, Milwaukee, Wisconsin, 53226.
Protein Sci. 2017 Oct;26(10):1974-1983. doi: 10.1002/pro.3234. Epub 2017 Jul 25.
Tetratricopeptide repeat (TPR) domains are ubiquitous protein interaction domains that adopt a modular antiparallel array of α-helices. The TPR fold typically adopts a monomeric state, and consensus TPRs sequences successfully fold into the expected monomeric topology. The versatility of the TPR fold also supports different quaternary structures, which may function as regulatory switches. One example is yeast mitochondrial fission 1 (Fis1) that appears to interconvert between monomer and dimer states in regulating division of peroxisomes and mitochondria. Whether human Fis1 can also interconvert like the yeast molecule is unknown. A TPR consensus proline residue present in human Fis1 is absent in the yeast molecule and, when added, prevents yeast Fis1 dimerization suggesting that the TPR consensus proline might have persisted to prevent TPR oligomerization. Here, we address this question with human Fis1 and the consensus TPR protein CTPR3. We demonstrate that human Fis1 does not form a noncovalent dimer via its TPR domain, despite conditions that favor dimerization of the yeast protein. We also show that the presence of the consensus proline is not sufficient to forbid TPR dimerization. Lastly, an analysis of all available TPR protein structures (22 nonredundant structures, totaling 64 TPRs-42 with the consensus proline and 22 without) revealed that the consensus proline is not necessary for turn formation, but does favor shorter turns. This work suggests the TPR consensus proline is not to prevent oligomerization, but to favor tight turns between repeats.
四肽重复序列（TPR）结构域是普遍存在的蛋白质相互作用结构域，其采用模块化的反平行α-螺旋阵列。TPR折叠通常呈现单体状态，并且一致的TPR序列能够成功折叠成预期的单体拓扑结构。TPR折叠的多功能性还支持不同的四级结构，这些结构可能起调节开关的作用。一个例子是酵母线粒体分裂蛋白1（Fis1），它在调节过氧化物酶体和线粒体分裂时似乎在单体和二聚体状态之间相互转换。人类Fis1是否也能像酵母分子那样相互转换尚不清楚。人类Fis1中存在的一个TPR一致脯氨酸残基在酵母分子中不存在，当添加该残基时，会阻止酵母Fis1二聚化，这表明TPR一致脯氨酸可能一直存在以防止TPR寡聚化。在这里，我们用人Fis1和一致TPR蛋白CTPR3来解决这个问题。我们证明，尽管存在有利于酵母蛋白二聚化的条件，但人Fis1不会通过其TPR结构域形成非共价二聚体。我们还表明，一致脯氨酸的存在不足以禁止TPR二聚化。最后，对所有可用的TPR蛋白结构（22个非冗余结构，共64个TPR，其中42个带有一致脯氨酸，22个没有）的分析表明，一致脯氨酸对于形成转角不是必需的，但确实有利于形成更短的转角。这项工作表明，TPR一致脯氨酸不是为了防止寡聚化，而是为了有利于重复序列之间形成紧密转角。
