SPRY domain-containing SOCS box (SSB) protein interaction with Par-4: Structure and biochemical implications

细胞因子信号转导抑制因子（SOCS）蛋白是负调节激素和生长因子作用的细胞内分子，并且其功能重要性已在许多生理学研究中得到证实。SOCS盒是SOCS蛋白的一小部分，据信其促进SOCS靶蛋白的降解。含SPRY结构域的SOCS盒蛋白-2（SSB-2）是大SOCS家族（SSB-1至-4）中的四种蛋白质之一，其具有SOCS盒和中央SPRY结构域。SPRY结构域介导与细胞内其他蛋白质的相互作用。已知超过300种蛋白质含有SPRY结构域。我们最近使用核磁共振（NMR）光谱法确定了作为SSB-2一部分的SPRY结构域的第一个原子结构。我们进一步确定Par-4（前列腺凋亡反应-4）作为SSB-1，-2和-4的新的和直接的蛋白结合伴侣，但不是SSB-3。广泛的突变分析随后确定了一系列SSB-2突变体，不能结合Par-4，但保留了结构完整性。癌细胞通过一系列遗传事件发展，并逃避程序性细胞死亡或凋亡，继续不适当地生长。Par-4最初被发现是在经历凋亡的前列腺癌细胞中上调的基因，并且主要表现为使癌细胞对凋亡刺激物敏感。该提案旨在进一步研究SSB-Par-4结合。将确定复合物的3D结构，并表征这种相互作用的生化后果。如果SSB蛋白调节Par-4水平，那么SSB-Par-4结合的化学破坏可能会导致Par-4蛋白水平的增加，使癌细胞更容易被细胞毒性药物杀死。

The suppressor of cytokine signalling (SOCS) proteins, are intracellular molecules that negatively regulate hormone and growth factor action, and whose functional importance has been borne out in many physiological studies. The SOCS box is a small part of the SOCS proteins that is believed to facilitate degradation of SOCS target proteins. The SPRY domain-containing SOCS box protein-2 (SSB-2) is one of four proteins within the greater SOCS family (SSB-1 to -4), which have a SOCS box and a central SPRY domain. The SPRY domain mediates interaction with other proteins within the cell. Over 300 proteins are known to contain a SPRY domain. We recently determined the first atomic structure of a SPRY domain as part of SSB-2, using nuclear magnetic resonance (NMR) spectroscopy. We further identified Par-4 (prostate apoptosis response-4) as a novel and direct protein binding partner for SSB-1, -2 and -4, but not SSB-3. Extensive mutational analysis subsequently identified a series of SSB-2 mutants that were unable to bind Par-4 but retained structural integrity. Cancer cells develop through a series of genetic events and escape programmed cell death or apoptosis, continuing to grow inappropriately. Par-4 was originally discovered as a gene up-regulated in prostate cancer cells undergoing apoptosis and primarily appears to sensitise cancer cells to apoptotic stimuli. This proposal aims to further investigate SSB-Par-4 binding. The 3D structure of the complex will be determined and biochemical consequences of this interaction characterised. If SSB proteins regulate Par-4 levels, then chemical disruption of SSB-Par-4 binding could potentially result in an increase in Par-4 protein levels, making cancer cells more susceptible to killing by cytotoxic drugs.