Sharif Mohamed, Greenberg Lydia, Bangs James
Department of Biochemistry, Jacobs School of Medicine and Biomedical Sciences, University at Buffalo, 955 Main Street, Buffalo, NY 14203, USA.
Department of Microbiology and Immunology, Jacobs School of Medicine and Biomedical Sciences, University at Buffalo, 955 Main Street, Buffalo, NY 14203, USA.
Open Biol. 2025 Feb;15(2):240324. doi: 10.1098/rsob.240324. Epub 2025 Feb 26.
Secretory cargos are exported from the ER via COPII-coated vesicles that have an inner matrix of Sec23/Sec24 heterotetramers and an outer cage of Sec13/Sec31 heterotetramers. In addition to COPII, Sec13 is part of the nuclear pore complex (NPC) and the regulatory SEA/GATOR complex in eukaryotes, which typically have one Sec13 orthologue. The kinetoplastid parasite has two paralogues: TbSec13.1, an accepted component of both COPII and the NPC, and TbSec13.2. Little is known about TbSec13.2, but others have proposed that it, and its orthologue in the distantly related diplonemid , operate exclusively in the SEA/GATOR complex, and that this represents an evolutionary diversification of function unique to the euglenozoan protists. Using RNAi silencing in trypanosomes, we show both TbSec13s are essential. Knockdown of each dramatically and equally delays transport of GPI-anchored secretory cargo, indicating roles for both in COPII-mediated trafficking from the ER. Immunofluorescence and proximity labelling studies confirm that both TbSec13.1 and TbSec13.2 co-localize with TbSec24.1 to ER exit sites, and thus are functional components of the COPII machinery. Our findings indicate that TbSec13.2 function is not restricted to the SEA/GATOR complex in trypanosomes.
分泌性货物通过被COPII包被的囊泡从内质网输出，这些囊泡具有由Sec23/Sec24异源四聚体组成的内部基质和由Sec13/Sec31异源四聚体组成的外部笼状结构。除了COPII外，Sec13是真核生物中核孔复合体（NPC）和调节性SEA/GATOR复合体的一部分，真核生物通常有一个Sec13直系同源物。动基体寄生虫有两个旁系同源物：TbSec13.1，它是COPII和NPC公认的组成部分，以及TbSec13.2。人们对TbSec13.2了解甚少，但其他人提出，它及其在远亲双滴虫中的直系同源物仅在SEA/GATOR复合体中发挥作用，这代表了眼虫类原生生物特有的功能进化多样化。通过在锥虫中使用RNAi沉默，我们发现两个TbSec13都是必需的。对每个基因的敲低都会显著且同等程度地延迟糖基磷脂酰肌醇（GPI）锚定的分泌性货物的运输，表明两者在COPII介导的从内质网的运输中都发挥作用。免疫荧光和邻近标记研究证实，TbSec13.1和TbSec13.2都与TbSec24.1共定位于内质网出口位点，因此是COPII机制的功能组成部分。我们的研究结果表明，TbSec13.2的功能并不局限于锥虫中的SEA/GATOR复合体。
