O'Connor Matthew S, Safari Amin, Xin Huawei, Liu Dan, Songyang Zhou
Verna and Marrs McLean Department of Biochemistry and Molecular Biology, Baylor College of Medicine, One Baylor Plaza, Houston, TX 77030, USA.
Proc Natl Acad Sci U S A. 2006 Aug 8;103(32):11874-9. doi: 10.1073/pnas.0605303103. Epub 2006 Jul 31.
Mammalian telomeric proteins function through dynamic interactions with each other and telomere DNA. We previously reported the formation of a high-molecular-mass telomeric complex (the mammalian telosome) that contains the six core proteins TRF1, TRF2, RAP1, TIN2, POT1, and TPP1 (formerly named PTOP/PIP1/TINT1) and mediates telomere end-capping and length control. In this report, we sought to elucidate the mechanism of six-protein complex (or shelterin) formation and the function of this complex. Through reconstitution experiments, we demonstrate here that TIN2 and TPP1 are key components in mediating the six-protein complex assembly. We demonstrate that not only TIN2 but also TPP1 are required to bridge the TRF1 and TRF2 subcomplexes. Specifically, TPP1 helps to stabilize the TRF1-TIN2-TRF2 interaction and promote six-protein complex formation. Consistent with this model, overexpression of TPP1 enhanced TIN2-TRF2 association. Conversely, knocking down TPP1 reduced the ability of endogenous TRF1 to associate with the TRF2 complex. Our results suggest that coordinated interactions among TPP1, TIN2, TRF1, and TRF2 may ensure robust assembly of the telosome, telomere targeting of its subunits, and, ultimately, regulated telomere maintenance.
哺乳动物端粒蛋白通过彼此之间以及与端粒DNA的动态相互作用发挥功能。我们之前报道了一种高分子量端粒复合物（哺乳动物端粒体）的形成，该复合物包含六种核心蛋白TRF1、TRF2、RAP1、TIN2、POT1和TPP1（以前称为PTOP/PIP1/TINT1），并介导端粒末端封端和长度控制。在本报告中，我们试图阐明六蛋白复合物（或端粒保护蛋白）的形成机制及其功能。通过重组实验，我们在此证明TIN2和TPP1是介导六蛋白复合物组装的关键组分。我们证明不仅TIN2而且TPP1都是连接TRF1和TRF2亚复合物所必需的。具体而言，TPP1有助于稳定TRF1-TIN2-TRF2相互作用并促进六蛋白复合物的形成。与该模型一致，TPP1的过表达增强了TIN2与TRF2的结合。相反，敲低TPP1降低了内源性TRF1与TRF2复合物结合的能力。我们的结果表明，TPP1、TIN2、TRF1和TRF2之间的协同相互作用可能确保端粒体的稳健组装、其亚基的端粒靶向定位，并最终确保端粒维持的调控。
