Environmental light signals are sensed by multiple families of photoreceptors and transduced by largely unknown mechanisms to regulate plant development. In this report, genetic analysis suggested that light signals perceived by both phytochromes and a blue light receptor converge to repress the action of Arabidopsis COP9 in suppressing seedling photomorphogenesis. Molecular cloning of the gene revealed that COP9 encodes a novel protein of 197 amino acids whose expression is not regulated by light. COP9 functions as a large (> 560 kDa) complex(es) that is probably subjected to light modulation. In addition, COP8 and COP11 are required for either the COP9 complex formation or its stability. Therefore COP9, together with COP8 and COP11, defines a novel signaling step in mediating light control of plant development.
"It contains eight canonical subunits that are termed CSN1 through CSN8, according to the descending order of molecular weights. The complex was originally identified as an essential factor that regulates light-induced development in Arabidopsis thaliana (Chamovitz et al., 1996; Wei et al., 1994); since then, it has been shown to play a critical role in diverse cellular processes including early development, DNA repair, cytokine signaling, regulation of nuclear transport, cell-cycle progression, angiogenesis , and antigen-induced responses (Schwechheimer, 2004; Wei et al., 2008). The involvement of the CSN in multiple cellular pathways is tied to its biochemical function as a regulator of the ubiquitin proteasome degradation pathway (Adler et al., 2006). "
[Show abstract][Hide abstract] ABSTRACT: The highly conserved COP9 signalosome (CSN) complex is a key regulator of all cullin-RING-ubiquitin ligases (CRLs), the largest family of E3 ubiquitin ligases. Until now, it was accepted that the CSN is composed of eight canonical components. Here, we report the discovery of an additional integral and stoichiometric subunit that had thus far evaded detection, and we named it CSNAP (CSN acidic protein). We show that CSNAP binds CSN3, CSN5, and CSN6, and its incorporation into the CSN complex is mediated through the C-terminal region involving conserved aromatic residues. Moreover, depletion of this small protein leads to reduced proliferation and a flattened and enlarged morphology. Finally, on the basis of sequence and structural properties shared by both CSNAP and DSS1, a component of the related 19S lid proteasome complex, we propose that CSNAP, the ninth CSN subunit, is the missing paralogous subunit of DSS1.
"Cullin deneddylation is catalyzed by the COP9 (COnstitutively Photomorphogenic mutant 9) signalosome    (Figure 1). The COP9 signalosome (CSN) was initially discovered in a model plant Arabidopsis  . The CSN is a protein complex conserved from yeast to COP9 signalosome in vasculature 36 Am J Cardiovasc Dis 2015;5(1):33-52 humans and apparently evolved in parallel to the UPS. "
[Show abstract][Hide abstract] ABSTRACT: Disorders of vascular function contribute importantly to cardiovascular disease which represents a substantial cause of morbidity and mortality worldwide. An emerging paradigm in the study of cardiovascular diseases is that protein ubiquitination and turnover represent key pathological mechanisms. Our understanding of these processes in the vasculature is growing but remains incomplete. Since protein ubiquitination and turnover can represent a terminal event in the life of a given protein, entry into these pathways must be highly regulated. However, at present understanding of these regulatory mechanisms, particularly in the vasculature, is fragmentary. The COP9 (constitutive photomorphogenic mutant 9) signalosome (CSN) is a heteromeric protein complex implicated in the control of protein degradation. The CSN participates critically in the control of Cullin Ring Ligases (CRLs), at least in part via the detachment of a small protein, Nedd8 (deneddylation). CRLs are one of the largest groups of ubiquitin ligases, which represent the most selective control point for protein ubiquitination. Thus, the CSN by virtue of its ability to control the CRLs ubiquitin ligase activity is ideally positioned to effect selective modulation of protein turnover. This review surveys currently available data regarding the potential role of the CSN in control of vascular function. Data potentially linking the CSN to control of regulatory proteins involved in vascular smooth muscle proliferation and to vascular smooth muscle contraction are presented with the intent of providing potentially intriguing possibilities for future investigation.
American Journal of Cardiovascular Disease 06/2015; 5(1):33-52.
"The constitutive photomorphogenesis 9 (COP9) signalosome (CSN) was initially identified as a repressor of constitutive photomorphogenesis in Arabidopsis  , and subsequently found in a variety of eukaryotic organisms including Saccharomyces cerevisiae  , Schizosaccharomyces pombe , Caenorhabditis elegans , Drosophila melanogaster  and mammals  . The predominant biochemical function of the CSN complex is its isopeptidase catalytic activity, which deneddylates the ubiquitin-like protein NEDD8 of the Cullin–RING family of ubiquitin E3 ligases (CRLs) and thereby regulates the activity of CRLs. "
[Show abstract][Hide abstract] ABSTRACT: The mammalian COP9 signalosome is an eight-subunit (CSN1–CSN8) complex that plays essential roles in multiple cellular and physiological processes. CSN5 and CSN6 are the only two MPN (Mpr1-Pad1-N-terminal) domain-containing subunits in the complex. Unlike the CSN5 MPN domain, CSN6 lacks a metal-binding site and isopeptidase activity. Here, we report the crystal structure of the human CSN6 MPN domain. Each CSN6 monomer contains nine β sheets surrounded by three helices. Two forms of dimers are observed in the crystal structure. Interestingly, a domain swapping of β8 and β9 strands occurs between two neighboring monomers to complete a typical MPN fold. Analyses of the pseudo metal-binding motif in CSN6 suggest that the loss of two key histidine residues may contribute to the lack of catalytic activity in CSN6. Comparing the MPN domain of our CSN6 with that in the CSN complex shows that apart from the different β8–β9 conformation, they have minor conformational differences at two insertion regions (Ins-1 and Ins-2). Besides, the interacting mode of CSN6–CSN6 in our structure is distinct from that of CSN5–CSN6 in the CSN complex structure. Moreover, the functional implications for Ins-1 and Ins-2 are discussed.
Biochemical and Biophysical Research Communications 09/2014; 453(1). DOI:10.1016/j.bbrc.2014.09.046 · 2.30 Impact Factor
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