Menon Suchithra, Tsuge Tomohiko, Dohmae Naoshi, Takio Koji, Wei Ning
Department of Molecular, Cellular and Developmental Biology, Yale University, New Haven, Connecticut, USA.
BMC Biochem. 2008 Jan 3;9:1. doi: 10.1186/1471-2091-9-1.
Cullin-RING ubiquitin E3 ligases (CRLs) are regulated by modification of an ubiquitin-like protein, Nedd8 (also known as Rub1) on the cullin subunit. Neddylation is shown to facilitate E3 complex assembly; while un-neddylated cullins are bound by CAND1 that prevents recruitment of the substrates. The level of Nedd8 modification is critically dependent on the COP9 signalosome (CSN), an eight-subunit protein complex containing Nedd8 isopeptidase activity.
We report isolation of SAP130 (SF3b-3) as a CSN1 interacting protein. SAP130 is homologous to DDB1, and is a component of SF3b RNA splicing complex and STAGA/TFTC transcription complexes, but its specific function within these complexes is unknown. We show that SAP130 can interact with a variety of cullin proteins. It forms tertiary complexes with fully assembled CRL E3 complexes such as SCFSkp2, Elongin B/C -Cul2- VHL and Cul4-DDB complex by binding to both N-terminal and C-terminal domain of cullins. SAP130 preferentially associates with neddylated cullins in vivo. However knock-down of CAND1 abolished this preference and increased association of SAP130 with Cul2. Furthermore, we provide evidence that CSN regulates SAP130-Cul2 interaction and SAP130-associated polyubiquitinating activity.
SAP130 is a cullin binding protein that is likely involved in the Nedd8 pathway. The association of SAP130 with various cullin member proteins such as Cul1, Cul2 and Cul4A is modulated by CAND1 and CSN. As an established component of transcription and RNA processing complexes, we hypothesis that SAP130 may link CRL mediated ubiquitination to gene expression.
Cullin-RING泛素E3连接酶（CRLs）通过泛素样蛋白Nedd8（也称为Rub1）对cullin亚基的修饰来调控。已表明Neddylation促进E3复合物组装；而未被Nedd化的cullins被CAND1结合，从而阻止底物的募集。Nedd8修饰水平关键取决于COP9信号小体（CSN），这是一种含有Nedd8异肽酶活性的八亚基蛋白质复合物。
我们报告分离出SAP130（SF3b-3）作为一种与CSN1相互作用的蛋白。SAP130与DDB1同源，是SF3b RNA剪接复合物和STAGA/TFTC转录复合物的一个组分，但其在这些复合物中的具体功能尚不清楚。我们表明SAP130能与多种cullin蛋白相互作用。它通过结合cullins的N端和C端结构域，与完全组装好的CRL E3复合物如SCFSkp2、Elongin B/C -Cul2- VHL和Cul4-DDB复合物形成三元复合物。在体内，SAP130优先与被Nedd化的cullins结合。然而，敲低CAND1消除了这种偏好，并增加了SAP130与Cul2的结合。此外，我们提供证据表明CSN调节SAP130-Cul2相互作用以及与SAP130相关的多聚泛素化活性。
SAP130是一种cullin结合蛋白，可能参与Nedd8途径。SAP130与各种cullin成员蛋白如Cul1、Cul2和Cul4A的结合受CAND1和CSN调节。作为转录和RNA加工复合物的一个既定组分，我们推测SAP130可能将CRL介导的泛素化与基因表达联系起来。
