RetroSearch Browse

Home - News ( United States | United Kingdom | Italy | Germany ) - Football scores

Showing content from https://pubmed.ncbi.nlm.nih.gov/19945379/ below:

Rapid E2-E3 assembly and disassembly enable processive ubiquitylation of cullin-RING ubiquitin ligase substrates

. 2009 Nov 25;139(5):957-68. doi: 10.1016/j.cell.2009.10.030. Rapid E2-E3 assembly and disassembly enable processive ubiquitylation of cullin-RING ubiquitin ligase substrates

Affiliations

Affiliation

¹ Howard Hughes Medical Institute and the Division of Biology, 156-29, California Institute of Technology, Pasadena, CA 91125, USA.

PMID: 19945379
PMCID: PMC2804849
DOI: 10.1016/j.cell.2009.10.030

Item in Clipboard

Rapid E2-E3 assembly and disassembly enable processive ubiquitylation of cullin-RING ubiquitin ligase substrates

Gary Kleiger et al. Cell. 2009.

. 2009 Nov 25;139(5):957-68. doi: 10.1016/j.cell.2009.10.030. Affiliation

¹ Howard Hughes Medical Institute and the Division of Biology, 156-29, California Institute of Technology, Pasadena, CA 91125, USA.

PMID: 19945379
PMCID: PMC2804849
DOI: 10.1016/j.cell.2009.10.030

Item in Clipboard

Abstract

Degradation by the ubiquitin-proteasome system requires assembly of a polyubiquitin chain upon substrate. However, the structural and mechanistic features that enable template-independent processive chain synthesis are unknown. We show that chain assembly by ubiquitin ligase SCF and ubiquitin-conjugating enzyme Cdc34 is facilitated by the unusual nature of Cdc34-SCF transactions: Cdc34 binds SCF with nanomolar affinity, nevertheless the complex is extremely dynamic. These properties are enabled by rapid association driven by electrostatic interactions between the acidic tail of Cdc34 and a basic 'canyon' in the Cul1 subunit of SCF. Ab initio docking between Cdc34 and Cul1 predicts intimate contact between the tail and the basic canyon, an arrangement confirmed by crosslinking and kinetic analysis of mutants. Basic canyon residues are conserved in both Cul1 paralogs and orthologs, suggesting that the same mechanism underlies processivity for all cullin-RING ubiquitin ligases. We discuss different strategies by which processive ubiquitin chain synthesis may be achieved.

PubMed Disclaimer

Figures
Figure 1

The kinetics of complex formation…

Figure 1

The kinetics of complex formation for human Cdc34 and RC ^CFP were dependent…

Figure 1

The kinetics of complex formation for human Cdc34 and RC^CFP were dependent on the ionic strength of the reaction buffer. The K_d (left panels) and k_off (right panels) were measured at equivalent ionic strength. k_on was then estimated from k_on = k_off/K_d. Error bars represent the standard deviation of at least duplicate measurements of all data points. (A) 50 mM NaCl. (B) 10 mM NaCl. (C) 100 mM NaCl.

Figure 2

The acidic tail promotes rapid…

Figure 2

The acidic tail promotes rapid assembly of functional Cdc34-SCF complexes. Ubiquitylation of a…

Figure 2

The acidic tail promotes rapid assembly of functional Cdc34-SCF complexes. Ubiquitylation of a mono-ubiquitylated β-Catenin peptide by SCF^β-TrCP plus either WT (A) or Cdc34-Δ190 (B). The plot on the right shows substrate turnover (min⁻¹) versus Cdc34 concentration. Error bars in (B) represent the standard deviation for duplicate values of data points. The experiments in panels A and C were performed in triplicate using a slightly different titration series each time. Therefore error bars are not given. The error of the measurement is the standard deviation of the three measurements. Representative data are shown. Note that nearly 100 percent of Cdc34-Δ190 protein became thioesterified with ubiquitin under these assay conditions (Table S2), even when assayed at 100 μM, the highest concentration of Cdc34-Δ190 in the titration series (Figure S7) (C) Competition binding experiment between a RC^CFP complex that was saturated with Lumio Green labeled WT Cdc34 and titrated with increasing concentrations of unlabeled Cdc34-Δ190. I is the fluorescence intensity. (D) The K_d for Cdc34 Δ221 (left panel) and k_off (right panel) were measured at equivalent NaCl (50 mM) and k_on was then estimated as in Figure 1.

Figure 3

The underside of cullin-RING complexes…

Figure 3

The underside of cullin-RING complexes is dominated by a basic canyon. (A) Molecular…

Figure 3

The underside of cullin-RING complexes is dominated by a basic canyon. (A) Molecular surface representation of a modeled SCF complex with the Cdc34 catalytic domain docked on the RING subunit. Arrows identify the location of the KR claw (see Figures 4e and Figure 5). The model was generated by homology modeling the Cdc34 and Rbx1 subunits to the UbcH7-Cbl x-ray structure and by structural alignment of the cyclin E-Fbw7-Skp1 x-ray structure to the Skp1-Cul1-Rbx1 structure (Hao et al., 2007; Zheng et al., 2002; Zheng et al., 2000) (B,C) Electrostatic surface plot of Cul1 CTD-Rbx1, where blue is positively-charged and red is negatively-charged. For reference, the orientation of the CTD in panel B is the same as the structure in the right panel of (A). (D) Electrostatic surface plot of Cul5 CTD-Rbx1. The orientation of Cul5 is similar to Cul1 in panel B. (E) Electrostatic surface plot of neddylated Cul5 CTD-Rbx1. The electrostatic potential was calculated with APBS (Baker et al., 2001) and figures were made in PYMOL. The range of the electrostatic potential (kT/e) is given at the bottom.

Figure 4

Cdc34’s acidic tail occupies Cul1’s…

Figure 4

Cdc34’s acidic tail occupies Cul1’s basic canyon. (A) The CTD of Cul1 and…

Figure 4

Cdc34’s acidic tail occupies Cul1’s basic canyon. (A) The CTD of Cul1 and Rbx1 are represented as molecular surfaces with the electrostatic potential shown. The catalytic domain of Cdc34, bound to Rbx1, is shown as yellow ribbons. The acidic tail residues are yellow balls-and-sticks. Acidic residues are red. Cys 227 of Cdc34 is cyan. All other residues in the tail are yellow. (B) Magnified view of (A), showing the tight molecular interface between the tail residues and the Cul1 basic canyon. (C) Histogram showing the binned frequencies for the distance between Cα atoms of K679 of Cul1 and Cys 227 of Cdc34 for either the 20 models with the lowest binding interaction energy, the 100 lowest, or all 28,574 models generated. (D) In vitro cross-linking between WT or K679C SCF and either WT or C227S Cdc34. Reactions were resolved by SDS-PAGE and immunoblotted with antibodies against the indicated proteins. The arrow indicates the cross-linked product between Cul1 CTD and WT Cdc34. (E) Molecular surface representation displaying the phylogenetic conservation of residues in Cul1. Residue positions are colored according to the degree of sequence similarity found in a multiple sequence alignment of five Cul1 orthologs (Saccharomyces cerevisiae, Schizosaccharomyces pombe, Drosophila melanogaster, Caenorhabditis elegans, human) and human Cul2-Cul5. Bright yellow residues are conserved in all nine cullins whereas deep blue residues are unique to human Cul1. The Rbx1 subunit is shown as a gray ribbon diagram. Residues forming the KR claw are located with black arrows.

Figure 5

Cul1’s KR claw mediates the…

Figure 5

Cul1’s KR claw mediates the function of Cdc34’s acidic tail. (A) Ubiquitylation of…

Figure 5

Cul1’s KR claw mediates the function of Cdc34’s acidic tail. (A) Ubiquitylation of a mono-ubiquitylated β-Catenin peptide by KKR SCF. Titration of WT Cdc34 on KKR SCF is shown. The plot on the right shows substrate turnover (min⁻¹) versus Cdc34 concentration. (B) Time course of β-Catenin peptide ubiquitylation by 0.75 μM UbcH5c in the presence of either WT or KKR SCF. UbcH5c was used below its K_m to sensitize detection of subtle perturbations to UbcH5c-SCF complex formation. (C) Same as (B) except 9 μM Cdc34-Δ190 (also below its K_m) and mono-ubiquitylated β-Catenin peptide substrate were used. Error bars represent the standard deviation of at least duplicate measurements of all data points. (D) Single encounter ubiquitylation reaction with yeast SCF^Cdc4 comparing Δ230 and Δ210 mutants of yeast Cdc34. Pre: labeled cyclin E peptide was pre-incubated with SCF^Cdc4 and unlabeled competitor prior to initiating the reaction by adding a mixture of E1/E2/Ub/ATP. Post: same as Pre, except that the unlabeled competitor peptide was introduced via the E1/E2/Ub/ATP mix.

Figure 6

Schematic of four distinct mechanistic…

Figure 6

Schematic of four distinct mechanistic solutions that may enable polyubiquitylation of protein substrates…

Figure 6

Schematic of four distinct mechanistic solutions that may enable polyubiquitylation of protein substrates in a single encounter with enzyme. See text for details. (A) Rapid dynamics of E2 and E3 association and dissociation, an example of which is the CRLs and Cdc34. The protein substrate is orange and labeled with the letter S. In this example, rapid dynamics are facilitated through the negatively charged acidic tail on E2 (red) and the positively charged region on the E3 (blue). (B) E2 never fully dissociates and is recharged while bound to ubiquitin ligase. (C) en bloc transfer of pre-assembled chain. (D) Substrate is first mono-ubiquitylated by a conventional ubiquitin ligase, after which substrate can bind a chain-elongating ubiquitin ligase to complete polyubiquitin chain formation.