Biochemical Institute, Christian-Albrechts-University of Kiel, Kiel, Germany.
Institute of Physiological Chemistry, Technische Universität Dresden, Dresden, Germany.
EMBO Rep. 2019 Mar;20(3). doi: 10.15252/embr.201846449. Epub 2019 Feb 7.
Signal peptide peptidase (SPP) and the four homologous SPP-like (SPPL) proteases constitute a family of intramembrane aspartyl proteases with selectivity for type II-oriented transmembrane segments. Here, we analyse the physiological function of the orphan protease SPPL2c, previously considered to represent a non-expressed pseudogene. We demonstrate proteolytic activity of SPPL2c towards selected tail-anchored proteins. Despite shared ER localisation, SPPL2c and SPP exhibit distinct, though partially overlapping substrate spectra and inhibitory profiles, and are organised in different high molecular weight complexes. Interestingly, SPPL2c is specifically expressed in murine and human testis where it is primarily localised in spermatids. In mice, SPPL2c deficiency leads to a partial loss of elongated spermatids and reduced motility of mature spermatozoa, but preserved fertility. However, matings of male and female mice exhibit reduced litter sizes. Using proteomics we identify the sarco/endoplasmic reticulum Ca-ATPase (SERCA2)-regulating protein phospholamban (PLN) as a physiological SPPL2c substrate. Accumulation of PLN correlates with a decrease in intracellular Ca levels in elongated spermatids that likely contribute to the compromised male germ cell differentiation and function of mice.
信号肽肽酶 (SPP) 和四个同源的 SPP 样 (SPPL) 蛋白酶构成了一个具有跨膜 II 型选择性的跨膜天冬氨酸蛋白酶家族。在这里，我们分析了先前被认为是无表达假基因的孤儿蛋白酶 SPPL2c 的生理功能。我们证明了 SPPL2c 对选定的尾部锚定蛋白具有蛋白水解活性。尽管具有共同的 ER 定位，但 SPPL2c 和 SPP 表现出不同的、尽管部分重叠的底物谱和抑制谱，并且组织在不同的高分子量复合物中。有趣的是，SPPL2c 在鼠和人睾丸中特异性表达，主要在精母细胞中定位。在小鼠中，SPPL2c 缺失导致长形精母细胞部分丢失和成熟精子运动能力降低，但生育力保存。然而， 雄性和雌性 小鼠的交配导致窝仔数减少。使用蛋白质组学，我们鉴定出肌浆/内质网 Ca-ATP 酶 (SERCA2) 调节蛋白磷酸化酶 (PLN) 为 SPPL2c 的生理底物。PLN 的积累与长形精母细胞中细胞内 Ca 水平的降低相关，这可能导致受损的雄性生殖细胞分化和 小鼠的功能障碍。
