COP9信号传导体与调节盖子复合体的进化

COP9信号传导体和26S蛋白酶体的调节盖子复合体皆为含有8个亚基的蛋白复合体,在真核生物体中普遍存在,它们的相应亚基在大小和氨基酸序列上具有一一对应关系.从NCBI站点的所有数据库中获得了裂殖酵母、酿酒酵母、线虫、果蝇、哺乳动物和拟南芥等多种生物的复合体的亚基序列共8组.COP9信号传导体与调节盖子复合体相应亚基之间的氨基酸序列一致性大于12%,它们均具有一些保守的区域,而且保守位点分布均匀,表明它们来自于同一祖先.在基于氨基酸序列构建的系统发育树中,各组序列分别形成两个分支:一个分支由COP9信号传导体亚基和相似蛋白组成,另一分支由相应的调节盖子复合体亚基和相似蛋白构成.各个分支中单细胞生物的序列位于动、植物序列的根部,表明COP9信号传导体与调节盖子复合体的基因重复发生在真核单细胞生物和多细胞生物分化以前,并且二者的亚基基因沿各自的方向独立进化.几乎所有编码两个蛋白复合体的基因在基因组中均为单拷贝,第Ⅴ、Ⅵ组的亚基保守程度最高,暗示着它们在复合体中起着关键的作用.对COP9信号传导体和调节盖子复合体的相应亚基基因两两之间进行dN/dS的相关性分析,分别鉴定出21和15对亚基编码序列间具有显著的Pearson相关关系,推测其相应亚基间可能通过承担相互关联的重要的生物学功能而协同进化.     

COP9信号复合体:信号转导与蛋白质降解的接合器

COP9信号复合体(CSN)是细胞内高度保守的多亚基蛋白质复合物,主要定位于真核细胞的细胞核。在结构上与26S蛋白酶体“盖子”亚复合物高度相关。CSN的具体功能目前尚未明确,主要体现为两方面的活性：脱Nedd化作用和磷酸化作用;在细胞内同SCF遍在蛋白连接酶复合体等许多蛋白质复合物发生相互作用;调节多种信号分子靶向遍在蛋白-26S蛋白酶体的稳定性。因此,CSN是连接信号转导与蛋白质降解的分子平台。     

植物COP9信号复合体的结构特征和功能

文章介绍植物COP9信号复合体(CSN)的结构特征及其与19S"盖子"结构相互关系,以及CSN参与的NEDD化/去NEDD化的过程研究进展。     

新生隐球菌COP9复合体基因CSN6的敲除与鉴定

目的构建新生隐球菌COP9复合体蛋白元件Csn6的基因同源重组敲除框,并通过基因枪转化系统敲除CSN6基因。方法应用生物信息学方法获得COP9复合体蛋白元件的基因信息,采用套叠PCR的方法,构建包含报告基因NEO和CSN6基因ORF两侧上下游同源DNA片段的同源重组框。应用基因枪将其转化入新生隐球菌感受态细胞,通过PCR和DNA测序对遗传霉素(G418)耐受的阳性克隆子进行筛选与验证。结果成功构建了新生隐球菌基因突变株csn6裣。结论 COP9复合体亚基CSN6基因突变株的构建,为今后新生隐球菌COP9复合体的分子致病机制研究奠定基础。     

The COP/DET/FUS proteins-regulators of eukaryotic growth and development

Eleven recessive mutant loci define the class of cop / det / fus mutants of Arabidopsis. The cop / det / fus mutants mimic the phenotype of light-grown seedlings when grown in the dark. At least four cop / det / fus mutants carry mutations in subunits of the COP9 signalosome, a multiprotein complex paralogous to the 'lid' subcomplex of the 26S proteasome. COP1, another COP/DET/FUS protein, is itself not a subunit of the COP9 signalosome. In the dark, COP1 accumulates in the nucleus where it is required for the degradation of the HY5 protein, a positive regulator of photomorphogenesis. In the light, COP1 is excluded from the nucleus and the constitutively nuclear HY5 protein can accumulate. Nuclear accumulation of COP1 and degradation of HY5 are impaired in the cop / det / fus mutants that carry mutations in subunits of the COP9 signalosome. Although the cellular function of the COP/DET/FUS proteins is not yet well understood, taken together the current findings suggest that the COP/DET/FUS proteins repress photomorphogenesis in the dark by mediating specific protein degradation.     

COP9 signalosome: Discovery,conservation, activity,and function

The COP9 signalosome(CSN)is a conserved protein complex,typically composed of eight subunits(designated as CSN1 to CSN8)in higher eukaryotes such as plants and animals,but of fewer subunits in some lower eukaryotes such as yeasts.The CSN complex is originally identified in plants from a genetic screen for mutants that mimic light-induced photomorphogenic development when grown in the dark.The CSN complex regulates the activity of cullin-RING ligase(CRL)families of E3 ubiquitin ligase complexes,and play critical roles in regulating gene expression,cell proliferation,and cell cycle.This review aims to summarize the discovery,composition,structure,and function of CSN in the regulation of plant development in response to external(light and temperature)and internal cues(phytohormones).     

A gain-of-function phenotype conferred by over-expression of functional subunits of the COP9 signalosome in Arabidopsis

The COP9 signalosome is a conserved cellular regulator present in diverse organisms. To understand the structural and functional relationship of the COP9 signalosome with its subunits, we expressed in wild-type and mutant Arabidopsis backgrounds two orthologues of subunit 1, rice FUS6 (rFUS6) and human GPS1, and Arabidopsis subunit 8 (COP9). In Arabidopsis, rFUS6 can functionally replace Arabidopsis endogenous FUS6 to form the COP9 signalosome complex and rescue the null fus6-1 mutant phenotype. Moreover, light-grown rFUS6 over-expression seedlings displayed longer hypocotyls and reduced anthocyanin accumulation in comparison to wild-type seedlings, which is opposite to the fus6/cop11 mutant phenotype. The long-hypocotyl phenotype was also observed in transgenic seedlings over-expressing Arabidopsis COP9. This finding indicates that over-expression of a functional subunit 1 or subunit 8 of the COP9 signalosome confers a gain-of-function phenotype relative to the complex. Human GPS1, when expressed in the fus6-1 null mutant of Arabidopsis, can assemble into a chimeric COP9 signalosome at low efficiency, demonstrating the structural conservation of the complexes between human and Arabidopsis. This low-abundancy chimeric complex is insufficient to fully rescue the mutant but is able to attenuate the mutant severity.     

Regulation of COP1 nuclear localization by the COP9 signalosome via direct interaction with CSN1

COP1 and COP9 signalosome (CSN) are key regulators of plant light responses and development. Deficiency in either COP1 or CSN causes a constitutive photomorphogenic phenotype. Through coordinated actions of nuclear- and cytoplasmic-localization signals, COP1 can respond to light signals by differentially partitions between nuclear and cytoplasmic compartments. Previous genetic analysis in Arabidopsis indicated that the nuclear localization of COP1 requires CSN, an eight-subunit heteromeric complex. However the mechanism underlying the functional relationship between COP1 and CSN is unknown. We report here that COP1 weakly associates with CSN in vivo . Furthermore, we report on the direct interaction involving the coiled-coil domain of COP1 and the N-terminal domain of the CSN1 subunit. In onion epidermal cells, expression of CSN1 can stimulate nuclear localization of GUS-COP1, and the N-terminal domain of CSN1 is necessary and sufficient for this function. Moreover, CSN1-induced COP1 nuclear localization requires the nuclear-localization sequences of COP1, as well as its coiled-coil domain, which contains both the cytoplasmic localization sequences and the CSN1 interacting domain. We also provide genetic evidence that the CSN1 N-terminal domain is specifically required for COP1 nuclear localization in Arabidopsis hypocotyl cells. This study advances our understanding of COP1 localization, and the molecular interactions between COP1 and CSN.     

The COP9 signalosome-mediated deneddylation is stimulated by caspases during apoptosis

In concert with the ubiquitin (Ub) proteasome system (UPS) the COP9 signalosome (CSN) controls the stability of cellular regulators. The CSN interacts with cullin-RING Ub ligases (CRLs) consisting of a specific cullin, a RING protein as Rbx1 and substrate recognition proteins. The Ub-like protein Nedd8 is covalently linked to cullins and removed by the CSN-mediated deneddylation. Cycles of neddylation and deneddylation regulate CRLs. Apoptotic stimuli cause caspase-dependent modifications of the UPS. However, little is known about the CSN during apoptosis. We demonstrate in vitro and in vivo that CSN6 is cleaved most effectively by caspase 3 at D₂₃ after 2–3 h of apoptosis induced by anti-Fas-Ab or etoposide. CSN6 processing occurs in CSN–CRL complexes and is followed by the cleavage of Rbx1, the direct interaction partner of CSN6. Caspase-dependent cutting of Rbx1 is accompanied by decrease of neddylated proteins in Jurkat T cells. Another functional consequence of CSN6 cleavage is the enhancement of CSN-mediated deneddylating activity causing deneddylation of cullin 1 in cells. The CSN-associated deubiquitinating as well as kinase activity remained unchanged in presence of active caspase 3. The cleavage of Rbx1 and increased deneddylation of cullins inactivate CRLs and presumably stabilize pro-apoptotic factors for final apoptotic steps. Bettina K. J. Hetfeld and Andreas Peth contributed equally.     

The COP9 signalosome coerces autophagy and the ubiquitin-proteasome system to police the heart

We demonstrated for the first time that the COP9 signalosome (COPS) controls the degradation of a surrogate and a bona fide misfolded protein in the cytosol of cardiomyocytes likely via supporting ubiquitination by CUL/cullin-RING ligases, and that Cops8 hypomorphism exacerbates cardiac proteinopathy in mice, in which autophagic impairment appears to be in play. It will be extremely imprtant to investigate cardiac ablation of another Cops gene to decipher whether COPS8 deficiency phenotypes are attributable to the COPS or unique to COPS8.