College of Health and Life Sciences, Hamad Bin Khalifa University, Doha, Qatar.
Faculty of Life Sciences, University of Manchester, Manchester, M13 9PT, UK.
Sci Rep. 2021 May 12;11(1):10133. doi: 10.1038/s41598-021-89439-2.
KASH5 is the most recently identified member of the KASH domain family of tail anchored, outer nuclear membrane (ONM) and endoplasmic reticulum (ER) proteins. During meiosis prophase I, KASH5 and SUN1 form a complex that spans the nuclear envelope and which links the telomeres of meiotic chromosomes to cytoplasmic dynein. This connection is essential for homologous chromosome dynamics and pairing. A recent study identified a variant in human KASH5 (L535Q) that correlated with male infertility associated with azoospermia. However, no molecular mechanism was described. Here, we report that this amino acid substitution, within the KASH5 transmembrane domain (TMD) has no predicted effects on secondary structure. However, the overall hydrophobicity of the L535Q TMD, is calculated to be lower than the wild-type KASH5, based on the GES (Goldman-Engelman-Steitz) amino acid hydrophobicity scale. This change in hydrophobicity profoundly affects the subcellular localization of KASH5. Through a series of amino acid substitution studies, we show that the L535Q substitution perturbs KASH5 localization to the ER and ONM and instead results in mistargeting to the mitochondria membrane. We suggest that this mislocalization accounts for the infertility and azoospermia phenotype in patients.
KASH5 是最近发现的 KASH 结构域家族的成员之一，该家族的蛋白尾部锚定于核外膜（ONM）和内质网（ER）。在减数分裂前期 I 中，KASH5 和 SUN1 形成一个跨越核膜的复合物，将减数分裂染色体的端粒与细胞质动力蛋白连接起来。这种连接对于同源染色体的动力学和配对至关重要。最近的一项研究发现，人类 KASH5（L535Q）的一个变体与无精子症相关的男性不育症相关。然而，没有描述分子机制。在这里，我们报告说，该氨基酸取代位于 KASH5 的跨膜结构域（TMD）内，对二级结构没有预测影响。然而，根据 GES（戈德曼-恩格尔曼-施泰茨）氨基酸疏水性尺度，L535Q TMD 的整体疏水性计算值低于野生型 KASH5。这种疏水性的变化会严重影响 KASH5 的亚细胞定位。通过一系列氨基酸取代研究，我们表明 L535Q 取代会破坏 KASH5 向 ER 和 ONM 的定位，而不是导致错误靶向线粒体膜。我们认为这种定位错误导致了患者的不育和无精子症表型。
