Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:3.4.25.1 (proteasome)
28,817 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

All developmental transitions throughout the life cycle of a plant are influenced by light. In Arabidopsis, multiple photoreceptors including the UV-A/blue-sensing cryptochromes (cry1-2) and the red/far-red responsive phytochromes (phyA-E) monitor the ambient light conditions. Light-regulated protein stability is a major control point of photomorphogenesis. The ubiquitin E3 ligase COP1 (constitutively photomorphogenic 1) regulates the stability of several light-signaling components. HFR1 (long hypocotyl in far-red light) is a putative transcription factor with a bHLH domain acting downstream of both phyA and the cryptochromes. HFR1 is closely related to PIF1, PIF3, and PIF4 (phytochrome interacting factor 1, 3 and 4), but in contrast to the latter three, there is no evidence for a direct interaction between HFR1 and the phytochromes. Here, we show that the protein abundance of HFR1 is tightly controlled by light. HFR1 is an unstable phosphoprotein, particularly in the dark. The proteasome and COP1 are required in vivo to degrade phosphorylated HFR1. In addition, HFR1 can interact with COP1, consistent with the idea of COP1 directly mediating HFR1 degradation. We identify a domain, conserved among several bHLH class proteins involved in light signaling , as a determinant of HFR1 stability. Our physiological experiments indicate that the control of HFR1 protein abundance is important for a normal de-etiolation response.
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PMID:The degradation of HFR1, a putative bHLH class transcription factor involved in light signaling, is regulated by phosphorylation and requires COP1. 1562 Jun 59

Light signals perceived by the phytochrome (phy) family of sensory photoreceptors control multiple aspects of plant development. Recently, PIF1, a phy-interacting basic helix-loop-helix (bHLH) transcription factor, has been shown to negatively regulate facets of the photomorphogenesis of seedlings. Moreover, the transcriptional activation activity of PIF1 is reduced in a phy-dependent manner. In this study we use the luciferase (LUC) activity of the LUC-PIF1 fusion protein as an indicator of the stability of PIF1 in various light conditions. We found that the activity of LUC-PIF1 in both transient and stable transgenic lines is rapidly reduced in light, while the LUC-only control is stable under the same conditions, suggesting that PIF1 is degraded in response to light. Fluence-rate response curves indicate that PIF1 degradation is very sensitive to the quality and quantity of light. The half-life of PIF1 is about 16 min under 10 micromol m-2 sec-1 red light. PIF1 reaccumulates in the subsequent dark period after light-induced degradation, signifying that PIF1 not only functions in the dark and during the transition from etiolated to de-etiolated growth, but may also function during diurnal cycles. Inhibitors of the 26S proteasome increased the stability of PIF1, indicating that degradation of PIF1 is mediated by the ubiquitin-26S proteasome pathway. Further, de novo protein synthesis is not required for degradation of PIF1, as the presence of cycloheximide does not prevent degradation of PIF1 in the light. Taken together, these results suggest that the light signals perceived by phys induce the degradation of PIF1 and other phy-interacting factors to optimize photomorphogenesis.
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PMID:PIF1 is regulated by light-mediated degradation through the ubiquitin-26S proteasome pathway to optimize photomorphogenesis of seedlings in Arabidopsis. 1635 94

Phytochrome (phy) family of photoreceptors is a broad sensor of environmental light signals that promote photomorphogenic development of plants. Phytochrome Interacting Factors (PIFs), bHLH family of transcription factors, repress photomorphogenesis in the dark in an overlapping manner. Phytochromes interact with PIFs in response to light and induce rapid phosphorylation, poly-ubiquitylation and degradation of PIFs through the ubiquitin/26S proteasome pathway to promote photomorphogenesis. Structure-function analyses with PIF family members revealed that multiple domains are necessary for the light-induced phosphorylation and degradation of PIFs. CK2, a ubiquitious Ser/Thr kinase, phosphorylates PIF1 independent of light. In addition, PIF1 mutants deficient in CK2 phosphorylation sites are still robustly phosphorylated but not efficiently degraded in response to light. These data suggest that multiple kinases phosphorylate PIF1 to promote light-induced degradation and photomorphogenesis.
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PMID:Multiple kinases promote light-induced degradation of PIF1. 2175 14

Proteolytic processing of viral membrane proteins is common among enveloped viruses and facilitates virus entry. The Autographa californica multicapsid nucleopolyhedrovirus (AcMNPV) occlusion-derived virus (ODV) protein P74 is part of a complex of essential peroral infectivity factors (PIFs). Here we report that P74 is efficiently cleaved into two fragments of about equal size by an occlusion body (OB) endogenous alkaline protease during ODV release when AcMNPV OBs are derived from larvae. The cleavage is specific for P74, since the other known peroral infectivity factors in the same complex (PIF1, PIF2, and PIF3) were not cleaved under the same conditions. P74 cleavage was not observed in OBs produced in three different insect cell lines, suggesting a larval host origin of the responsible protease. P74 in OBs produced in larvae of two different host species was cleaved into fragments with the same apparent molecular mass, indicating that the virus incorporates a similar alkaline protease from different hosts. Coimmunoprecipitation analysis revealed that the two P74 subunit fragments remain associated with the recently discovered PIF complex. We propose that under in vivo ODV infection conditions, P74 undergoes two sequential cleavage events, the first one being performed by an ODV-associated host alkaline protease and the second carried out by trypsin in the host midgut.
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PMID:In situ cleavage of baculovirus occlusion-derived virus receptor binding protein P74 in the peroral infectivity complex. 2184 53

In Arabidopsis thaliana, the cryptochrome and phytochrome photoreceptors act together to promote photomorphogenic development. The cryptochrome and phytochrome signaling mechanisms interact directly with CONSTITUTIVELY PHOTOMORPHOGENIC1 (COP1), a RING motif-containing E3 ligase that acts to negatively regulate photomorphogenesis. COP1 interacts with and ubiquitinates the transcription factors that promote photomorphogenesis, such as ELONGATED HYPOCOTYL5 and LONG HYPOCOTYL IN FAR-RED1 (HFR1), to inhibit photomorphogenic development. Here, we show that COP1 physically interacts with PIF3-LIKE1 (PIL1) and promotes PIL1 degradation via the 26S proteasome. We further demonstrate that phyB physically interacts with PIL1 and enhances PIL1 protein accumulation upon red light irradiation, probably through suppressing the COP1-PIL1 association. Biochemical and genetic studies indicate that PIL1 and HFR1 form heterodimers and promote photomorphogenesis cooperatively. Moreover, we demonstrate that PIL1 interacts with PIF1, 3, 4, and 5, resulting in the inhibition of the transcription of PIF direct-target genes. Our results reveal that PIL1 stability is regulated by phyB and COP1, likely through physical interactions, and that PIL1 coordinates with HFR1 to inhibit the transcriptional activity of PIFs, suggesting that PIL1, HFR1, and PIFs constitute a subset of antagonistic basic helix-loop-helix factors acting downstream of phyB and COP1 to regulate photomorphogenic development.
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PMID:COP1 and phyB Physically Interact with PIL1 to Regulate Its Stability and Photomorphogenic Development in Arabidopsis. 2495 80

The phytochrome interacting factors (PIFs), a small group of basic helix-loop-helix transcription factors, repress photomorphogenesis both in the dark and light. Light signals perceived by the phytochrome family of photoreceptors induce rapid degradation of PIFs to promote photomorphogenesis. Here, we show that HECATE (HEC) proteins, another small group of HLH proteins, antagonistically regulate PIFs to promote photomorphogenesis. HEC1 and HEC2 heterodimerize with PIF family members. PIF1, HEC1, and HEC2 genes are spatially and temporally coexpressed, and HEC2 is localized in the nucleus. hec1, hec2, and hec3 single mutants and the hec1 hec2 double mutant showed hyposensitivity to light-induced seed germination and accumulation of chlorophyll and carotenoids, hallmark processes oppositely regulated by PIF1. HEC2 inhibits PIF1 target gene expression by directly heterodimerizing with PIF1 and preventing DNA binding and transcriptional activation activity of PIF1. Conversely, PIFs directly activate the expression of HEC1 and HEC2 in the dark, and light reduces the expression of these HECs possibly by degrading PIFs. HEC2 is partially degraded in the dark through the ubiquitin/26S-proteasome pathway and is stabilized by light. HEC2 overexpression also reduces the light-induced degradation of PIF1. Taken together, these data suggest that PIFs and HECs constitute a negative feedback loop to fine-tune photomorphogenesis in Arabidopsis thaliana.
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PMID:A Negative Feedback Loop between PHYTOCHROME INTERACTING FACTORs and HECATE Proteins Fine-Tunes Photomorphogenesis in Arabidopsis. 2707 31

Plants perceive red and far-red region of the light spectrum to regulate photomorphogenesis through a family of photoreceptors called phytochromes. Phytochromes transduce the light signals to trigger a cascade of downstream gene regulation in part via a subfamily of bHLH transcription factors called Phytochrome Interacting Factors (PIFs). As the repressors of light signaling pathways, most PIFs are phosphorylated and degraded through the ubiquitin/26S proteasome pathway in response to light. The mechanisms involved in the phosphorylation and degradation of PIFs have not been fully understood yet. Here we used an EMS mutagenesis and luminescent imaging system to identify mutants defective in the degradation of one of the PIFs, called PIF1. We identified five mutants named stable PIF (spf) that showed reduced degradation of PIF1 under light treatment in both luminescent imaging and immunoblot assays. The amounts of PIF1 in spf3, spf4, and spf5 were similar to a PIF1 missense mutant (PIF1-3M) that lacks interactions between PIF1 and phyA/phyB under light. The hypocotyl lengths of spf1 and spf2 were slightly longer under red light compared to the LUC-PIF1 control, while only spf1 displayed weak phenotype under far-red light conditions. Interestingly, the spf3, spf4, and spf5 displayed high abundance of PIF1, yet the hypocotyl lengths were similar to the wild type under these conditions. Cloning and characterization of these mutants will help identify key players in the light signaling pathways including, the light-regulated kinase(s) and the E3 ligase(s) necessary for the light-induced degradation of PIFs.
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PMID:A Protein-Based Genetic Screening Uncovers Mutants Involved in Phytochrome Signaling in Arabidopsis. 2749 59

The phytochrome-mediated regulation of photomorphogenesis under red and far-red light conditions involves both positively and negatively acting factors. The positively acting factors (e.g. HY5/HFR1/LAF1 and others) are degraded in the dark to prevent photomorphogenesis. By contrast, the negatively acting factors (e.g. phytochrome-interacting factors or PIFs) are degraded in response to light to promote photomorphogenesis. Here, we show that the negatively acting factor PIF1 is also degraded in the dark by direct heterodimerization with the positively acting factor HFR1. Conversely, PIF1 also promotes the degradation of HFR1 in darkness. PIF1 enhances the poly-ubiquitylation of HFR1 by COP1 in vivo and in vitro In addition, the reciprocal co-degradation of PIF1 and HFR1 is dependent on the 26S proteasome pathway in vivo Genetic evidence shows that the hfr1 mutant partially suppresses the constitutive photomorphogenic phenotypes of cop1-6 pif1 and of the quadruple mutant pifq both in the dark and in far-red light conditions. Taken together, these data uncover a co-degradation mechanism between PIFs and HFR1 that underlies photomorphogenic development in Arabidopsis thaliana.
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PMID:Reciprocal proteasome-mediated degradation of PIFs and HFR1 underlies photomorphogenic development in Arabidopsis. 2842 Jul 10

Baculoviridae is a family of large, enveloped, double-stranded DNA viruses that mostly infect insects. Occlusion-derived virus is a baculovirus viral phenotype that induces primary infection when ingested by the insect host per os. Several occlusion-derived viral membrane proteins, called per os infectivity factors, have been shown to be essential for oral infectivity. Here, we review advances in structure and function studies of P74,which was the first PIF to be identified and has been extensively investigated.P74 contains two transmembrane domains in its hydrophobic C terminus which play a role in transmembrane anchoring, and two conserved domains which are involved in P74 function.P74is efficiently cleaved by an occlusion body endogenous alkaline protease and a host trypsin during baculovirus release and its digestion products are loosely associated with a stable complex formed by PIF1,PIF2 and PIF3.As a baculovirus attachment protein,P74 binds to a specific receptor of approximately 35 kDa in brush border membrane vesicles, facilitating the internalization of baculovirus into host cells. Knowledge of P74 will improve our understanding of baculovirus primary infection, which will support the design of nonchemical strategies to block baculovirus transmission or suppress pest populations.
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PMID:[Structure and Function of the Baculovirus Per Os Infectivity Factor (PIF) P74]. 2999 43

Light signal provides the spatial and temporal information for plants to adapt to the prevailing environmental conditions. Alterations in light quality and quantity can trigger robust changes in global gene expression. In Arabidopsis thaliana, two groups of key factors regulating those changes in gene expression are CONSTITUTIVE PHOTOMORPHOGENESIS/DEETIOLATED/FUSCA (COP/DET/FUS) and a subset of basic helix-loop-helix transcription factors called PHYTOCHROME-INTERACTING FACTORS (PIFs). Recently, rapid progress has been made in characterizing the E3 ubiquitin ligases for the light-induced degradation of PIF1, PIF3 and PIF4; however, the E3 ligase(s) for PIF5 remains unknown. Here, we show that the CUL4^{COP 1- SPA} complex is necessary for the red light-induced degradation of PIF5. Furthermore, COP1 and SPA proteins stabilize PIF5 in the dark, but promote the ubiquitination and degradation of PIF5 in response to red light through the 26S proteasome pathway. Genetic analysis illustrates that overexpression of PIF5 can partially suppress both cop1-4 and spaQ seedling de-etiolation phenotypes under dark and red-light conditions. In addition, the PIF5 protein level cycles under both diurnal and constant light conditions, which is also defective in the cop1-4 and spaQ backgrounds. Both cop1-4 and spaQ show defects in diurnal growth pattern. Overexpression of PIF5 partially restores growth defects in cop1-4 and spaQ under diurnal conditions, suggesting that the COP1-SPA complex plays an essential role in photoperiodic hypocotyl growth, partly through regulating the PIF5 level. Taken together, our data illustrate how the CUL4^{COP 1- SPA} E3 ligase dynamically controls the PIF5 level to regulate plant development.
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PMID:Dynamic regulation of PIF5 by COP1-SPA complex to optimize photomorphogenesis in Arabidopsis. 3029 82


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