Ring flips of phenylalanine and tyrosine are a hallmark of protein dynamics. They report on transient breathing motions of proteins. In addition, flip rates also depend on stabilizing interactions in the ground state, like aromatic stacking or cation-π interaction. So far, experimental studies of ring flips have almost exclusively been performed on aromatic rings without stabilizing interactions. Here we investigate ring flip dynamics of Phe and Tyr in the aromatic cluster in GB1. We found that all four residues of the cluster, Y3, F30, Y45 and F52, display slow ring flips. Interestingly, F52, the central residue of the cluster, which makes aromatic contacts with all three others, is flipping significantly faster, while the other rings are flipping with the same rates within margin of error. Determined activation enthalpies and activation volumes of these processes are in the same range of other reported ring flips of single aromatic rings. There is no correlation of the number of aromatic stacking interactions to the activation enthalpy, and no correlation of the ring's extent of burying to the activation volume. Because of these findings, we speculate that F52 is undergoing concerted ring flips with each of the other rings.

中文翻译：

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通过芳族13C弛豫分散法研究了GB1芳族簇中的慢环翻转。

苯丙氨酸和酪氨酸的环翻转是蛋白质动力学的标志。他们报告了蛋白质的短暂呼吸运动。另外，翻转速率还取决于基态下的稳定相互作用，例如芳族堆积或阳离子-π相互作用。到目前为止，翻转环的实验研究几乎仅在芳香环上进行，而没有稳定相互作用。在这里，我们研究了GB1芳香族簇中Phe和Tyr的环翻转动力学。我们发现该簇的所有四个残基Y3，F30，Y45和F52均显示缓慢的环翻转。有趣的是，F52是团簇的中心残基，该残基与所有其他三个原子进行芳香接触，其翻转速度明显加快，而其他环以相同的速率在误差范围内翻转。这些过程的确定的活化焓和活化体积在单个芳香环的其他报道的环翻转的相同范围内。芳族堆积相互作用的数量与活化焓没有关系，并且环的掩埋程度与活化量也没有关系。基于这些发现，我们推测F52正在与其他每个环一起发生协同的环翻转。