Division of Hematology/Oncology, Indiana University School of Medicine, Indianapolis, Indiana, USA.
The Jackson Laboratory for Genomic Medicine, Farmington, Connecticut, USA.
Mol Cell Biol. 2020 May 28;40(12). doi: 10.1128/MCB.00652-19.
The LMO2/LDB1 macromolecular complex is critical in hematopoietic stem and progenitor cell specification and in the development of acute leukemia. This complex is comprised of core subunits of LMO2 and LDB1 as well as ingle-tranded DNA-inding rotein (SSBP) cofactors and DNA-binding asic elix-oop-elix (bHLH) and GATA transcription factors. We analyzed the steady-state abundance and kinetic stability of LMO2 and its partners via Halo protein tagging in conjunction with variant proteins deficient in binding their respective direct protein partners. We discovered a hierarchy of protein stabilities (with half-lives in descending order) as follows: LDB1 > SSBP > LMO2 > TAL1. Importantly, LDB1 is a remarkably stable protein that confers enhanced stability upon direct and indirect partners, thereby nucleating the formation of the multisubunit protein complex. The data imply that free subunits are more rapidly degraded than those incorporated within the LMO2/LDB1 complex. Our studies provided significant insights into LMO2/LDB1 macromolecular protein complex assembly and stability, which has implications for understanding its role in blood cell formation and for therapeutically targeting this complex in human leukemias.
LMO2/LDB1 大分子复合物在造血干细胞和祖细胞的特化以及急性白血病的发展中至关重要。该复合物由 LMO2 和 LDB1 的核心亚基以及单链 DNA 结合蛋白（SSBP）辅助因子和 DNA 结合碱性螺旋-环-螺旋（bHLH）和 GATA 转录因子组成。我们通过 Halo 蛋白标记与缺乏与其各自直接蛋白伴侣结合能力的变体蛋白结合，分析了 LMO2 及其伴侣的稳态丰度和动力学稳定性。我们发现了蛋白质稳定性的层次结构（半衰期按降序排列）如下：LDB1 > SSBP > LMO2 > TAL1。重要的是，LDB1 是一种非常稳定的蛋白质，它赋予直接和间接伴侣增强的稳定性，从而形成多亚基蛋白质复合物的核心。这些数据表明，游离亚基比那些包含在 LMO2/LDB1 复合物中的亚基更容易降解。我们的研究为 LMO2/LDB1 大分子蛋白质复合物的组装和稳定性提供了重要的见解，这对于理解其在血细胞形成中的作用以及在人类白血病中靶向该复合物具有重要意义。
