Ubiquitin-dependent regulation of COPII coat size and function

Department of Molecular and Cell Biology, University of California at Berkeley, California 94720, USA.
Nature (Impact Factor: 41.46). 02/2012; 482(7386):495-500. DOI: 10.1038/nature10822
Source: PubMed


Packaging of proteins from the endoplasmic reticulum into COPII vesicles is essential for secretion. In cells, most COPII vesicles are approximately 60-80 nm in diameter, yet some must increase their size to accommodate 300-400 nm procollagen fibres or chylomicrons. Impaired COPII function results in collagen deposition defects, cranio-lenticulo-sutural dysplasia, or chylomicron retention disease, but mechanisms to enlarge COPII coats have remained elusive. Here, we identified the ubiquitin ligase CUL3-KLHL12 as a regulator of COPII coat formation. CUL3-KLHL12 catalyses the monoubiquitylation of the COPII-component SEC31 and drives the assembly of large COPII coats. As a result, ubiquitylation by CUL3-KLHL12 is essential for collagen export, yet less important for the transport of small cargo. We conclude that monoubiquitylation controls the size and function of a vesicle coat.


Available from: Kanika Bajaj Pahuja
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    • "the finding that K33-ubiquitinated Crn7 binds Eps15 tUIM to promote the assembly of TGN-associated F-actin represents the first description of a cellular recognition mechanism and the first demonstration of a positive signaling function of this atypical ubiquitin chain. Cul3-family ubiquitin ligases often target substrates for proteasomal degradation but can also catalyze monoubiquitination on certain substrates (Beck et al., 2013; Herná ndez-Muñ oz et al., 2005; Jin et al., 2012). Our identification of the K33-ubiquitination by Cul3-KLHL20 complex expands the versatility of this family of ligases. "
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    ABSTRACT: Ubiquitin chains are formed as structurally distinct polymers via different linkages, and several chain types including K33-linkage remain uncharacterized. Here, we describe a role for K33-polyubiquitination in protein trafficking. We show that the Cullin 3 (Cul3) substrate adaptor KLHL20 is localized to the trans-Golgi network (TGN) and is important for post-Golgi trafficking by promoting the biogenesis of TGN-derived transport carriers. The Cul3-KLHL20 ubiquitin E3 ligase catalyzes a nondegradable, K33-linked polyubiquitination on coronin 7 (Crn7), which facilitates Crn7 targeting to TGN through a ubiquitin-dependent interaction with Eps15. Blockage of K33-chain formation, Crn7 ubiquitination, or disruption of Crn7-Eps15 interaction impairs TGN-pool F-actin assembly, a process essential for generating transport carriers. Enforced targeting of Crn7 to TGN bypasses the requirement of K33-ubiquitination for TGN-pool F-actin assembly and post-Golgi trafficking. Our study reveals a role of KLHL20-mediated K33-ubiquitination of Crn7 in post-Golgi transport and identifies a cellular recognition mechanism for this ubiquitin chain type.
    Molecular cell 04/2014; 54(4). DOI:10.1016/j.molcel.2014.03.035 · 14.02 Impact Factor
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    • "Structural data suggests a COPII cage diameter size of 60–80 nm [11], contrasting with findings of COPII-dependent export of collagen [12], which would require larger vesicles (reviewed in [13]). This has led to speculation that a specialized mechanism to accommodate bulky cargo is needed, and evidence supporting this has come with the recent discovery of a role for ubiquitin conjugation of Sec31 in the formation of enlarged COPII- vesicles facilitating collagen export [14]. How the COPII structures are retained at the ER exit sites in order to expand to a size large enough to accommodate bulk cargo remains unexplained. "
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    ABSTRACT: Coated vesicles mediate the traffic of secretory and membrane cargo proteins from the endoplasmic reticulum (ER) to the Golgi apparatus. The coat protein complex (COPII) involved in vesicle budding is constituted by a GTPase, Sar1, the inner coat components of Sec23/Sec24 and the components of the outer coat Sec13/Sec31A. The Ca(2+)-binding protein ALG-2 was recently identified as a Sec31A binding partner and a possible link to Ca(2+) regulation of COPII vesicle budding. Here we show that ALG-2/Ca(2+) is capable of attenuating vesicle budding in vitro through interaction with an ALG-2 binding domain in the proline rich region of Sec31A. Binding of ALG-2 to Sec31A and inhibition of COPII vesicle budding is furthermore dependent on an intact Ca(2+)-binding site at EF-hand 1 of ALG-2. ALG-2 increased recruitment of COPII proteins Sec23/24 and Sec13/31A to artificial liposomes and was capable of mediating binding of Sec13/31A to Sec23. These results introduce a regulatory role for ALG-2/Ca(2+) in COPII tethering and vesicle budding.
    PLoS ONE 09/2013; 8(9):e75309. DOI:10.1371/journal.pone.0075309 · 3.23 Impact Factor
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    • "However, as described above, the same E3 complex is also involved in ubiquitin-dependent proteolysis of other substrates like Gli2/3 (Chen et al, 2009a) or SRC-3 (Li et al, 2011), most likely via K48-linked polyubiquitin chains. Similarly, Aurora B and caspase-8 are regulated by nonproteolytic ubiquitylation and Sec31A and PLK1 are monoubiquitylated by CRL3s in human cells (Jin et al, 2009, 2012; Maerki et al, 2009; Beck et al, 2013). Another interesting example is the light intensity-dependent differential regulation of poly-versus mono-/multi-mono-ubiquitylation of PHOT1 by CRL3-NPH3 in plants (Roberts et al, 2011). "
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    ABSTRACT: Protein ubiquitylation is a post-translational modification that controls all aspects of eukaryotic cell functionality, and its defective regulation is manifested in various human diseases. The ubiquitylation process requires a set of enzymes, of which the ubiquitin ligases (E3s) are the substrate recognition components. Modular CULLIN-RING ubiquitin ligases (CRLs) are the most prevalent class of E3s, comprising hundreds of distinct CRL complexes with the potential to recruit as many and even more protein substrates. Best understood at both structural and functional levels are CRL1 or SCF (SKP1/CUL1/F-box protein) complexes, representing the founding member of this class of multimeric E3s. Another CRL subfamily, called CRL3, is composed of the molecular scaffold CULLIN3 and the RING protein RBX1, in combination with one of numerous BTB domain proteins acting as substrate adaptors. Recent work has firmly established CRL3s as major regulators of different cellular and developmental processes as well as stress responses in both metazoans and higher plants. In humans, functional alterations of CRL3s have been associated with various pathologies, including metabolic disorders, muscle, and nerve degeneration, as well as cancer. In this review, we summarize recent discoveries on the function of CRL3s in both metazoans and plants, and discuss their mode of regulation and specificities.
    The EMBO Journal 08/2013; 32(17). DOI:10.1038/emboj.2013.173 · 10.43 Impact Factor
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