Magnetic Resonance Center CERM, University of Florence, Via Luigi Sacconi 6, 50019 Sesto Fiorentino, Florence, Italy.
J Struct Biol. 2012 Oct;180(1):190-200. doi: 10.1016/j.jsb.2012.07.007. Epub 2012 Jul 25.
Twin CX(9)C proteins constitute a large protein family among all eukaryotes; are putative substrates of the mitochondrial Mia40-dependent import machinery; contain a coiled coil-helix-coiled coil-helix (CHCH) fold stabilized by two disulfide bonds as exemplified by three structures available for this family. However, they considerably differ at the primary sequence level and this prevents an accurate prediction of their structural models. With the aim of expanding structural information on CHCH proteins, here we structurally characterized human CHCHD5 and CHCHD7. While CHCHD5 has two weakly interacting CHCH domains which sample a range of limited conformations as a consequence of hydrophobic interactions, CHCHD7 has a third helix hydrophobically interacting with an extension of helix α2, which is part of the CHCH domain. Upon reduction of the disulfide bonds both proteins become unstructured exposing hydrophobic patches, with the result of protein aggregation/precipitation. These results suggest a model where the molecular interactions guiding the protein recognition between Mia40 and the disulfide-reduced CHCHD5 and CHCHD7 substrates occurs in vivo when the latter proteins are partially embedded in the protein import pore of the outer membrane of mitochondria.
双 CXC（9）C 蛋白构成了所有真核生物中一个庞大的蛋白质家族；被认为是线粒体 Mia40 依赖的输入机制的潜在底物；包含一个由两个二硫键稳定的卷曲螺旋-螺旋-卷曲（CHCH）折叠，这由该家族的三个结构得到例证。然而，它们在一级序列水平上有很大的差异，这使得对它们的结构模型的准确预测变得困难。为了扩展 CHCH 蛋白的结构信息，我们在这里对人源 CHCHD5 和 CHCHD7 进行了结构表征。虽然 CHCHD5 有两个弱相互作用的 CHCH 结构域，由于疏水性相互作用，这些结构域可以采样一系列有限的构象，但 CHCHD7 有第三个螺旋与螺旋 α2 的延伸部分疏水相互作用，这是 CHCH 结构域的一部分。当二硫键还原时，两种蛋白质都变得无结构，暴露出疏水区，导致蛋白质聚集/沉淀。这些结果表明，在体内，当 Mia40 与二硫键还原的 CHCHD5 和 CHCHD7 底物之间的蛋白质识别的分子相互作用发生时，可能存在一种模型，即当后者蛋白质部分嵌入线粒体外膜的蛋白质输入孔中时。
