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Global Pharmaceutical Research and Discovery, Abbott Laboratories, Abbott Park, Illinois 60064-6100, USA
Reprint requests to: Edward T. Olejniczak, Global Pharmaceutical Research and Discovery, Abbott Laboratories, 100 Abbott Park Road, Abbott Park, IL 60064-6100, USA; e-mail: Edward.olejniczak{at}abbott.com; fax: (847) 938-2478.
(RECEIVED March 13, 2003; FINAL REVISION April 11, 2003; ACCEPTED April 11, 2003)
1 These authors contributed equally to this work. ![]()
Article and publication are at http://www.proteinscience.org/cgi/doi/10.1110/ps.0382803.
Supplemental material: See www.proteinscience.org.
| Abstract |
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25% residue similarity. The signature C-terminal di-tyrosine residues in UBL5 are involved in the final ß sheet of the protein. This is very different to the di-glycine motif found in ubiquitin, which extends beyond the final ß sheet. In addition, we have confirmed an earlier report of an interaction between UBL5 and the cyclin-like kinase, CLK4, which we have determined is specific and does not extend to other cyclin-like kinase family members. Keywords: UBL5; beacon; ubiquitin; NMR spectroscopy; structure determination; cyclin-like kinase
Abbreviations: NMR, nuclear magnetic resonance NOE, nuclear Overhauser effect RMSD, root-mean-squared deviation CLK, cyclin-like kinase ppm, parts per million
| Introduction |
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Based on sequence homology and structure prediction algorithms it is predicted that the protein UBL5 has a structure similar to ubiquitin (Friedmann et al. 2001). The sequence similarity is, however, weak, and the protein does not contain the characteristic di-glycine residues at its C terminus that are required for ubiquitin-like modifiers to conjugate to their target proteins (Hochstrasser 1996; Jentsch and Pyrowolakis 2000; Glickman and Ciechanover 2002). The yeast ortholog of UBL5, HUB1, has been reported to have ubiquitin-like modifier activity (Jentsch and Pyrowolakis 2000; Dittmar et al. 2002). UBL5 has been shown to be interchangeable with HUB1 in a yeast-based assay that measured its ability to rescue HUB1 mutants from a mating projection defect (Dittmar et al. 2002). These data from yeast suggest that UBL5 like HUB1, covalently attaches to other proteins and based on its sequence does so in a manner distinct from the di-glycine containing ubiquitin-like proteins.
Although several predictions have been made for the structure of UBL5, no experimental data are available. Here, we describe the three-dimensional structure of UBL5 and compare it to that of ubiquitin. We also report on our studies of the interaction of UBL5 with CLK4 and other cyclin-like kinase family members using yeast two hybrid studies.
| Results |
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The only construct that grew on nonpermissive minimal medium was the CLK4 full-length construct, and not the C-terminally truncated splice variant. None of the aforementioned constructs grew on permissive minimal medium when transformed with the GAL4-activating domain alone, suggesting that the CLK4 interaction was specific to UBL5. Because the splice variant of CLK4 did not interact with UBL5, it can be assumed that the interaction between UBL5 and CLK4 is mediated by the C terminus of the protein, where the kinase domain resides. Interestingly, this is where CLK4 and, in particular CLK1, are the most similar in sequence. Because the interaction was detected using yeast two-hybrid screening it is still not known if the interaction is covalent or not.
Protein structure determination
An N-terminal His-tagged version of UBL5 was expressed in Escherichia coli, isotopically labeled, and purified. After cleavage of the His tag the protein was found to aggregate at concentrations above 0.1 mM over a wide pH range and was thus unsuitable for NMR structural studies. The uncleaved protein was stable and was used in the structural studies. The 15N HSQC spectrum of the tagged protein was essentially identical to that of the wild-type protein, indicating that the fold of the protein is preserved. The backbone and side-chain resonances of the protein were assigned from standard heteronuclear three-dimensional NMR experiments (see Materials and Methods) recorded on a protein sample that was uniformly labeled with 15N and 13C.
The structure of the UBL5 was determined from a total of 952 unambiguous NMR-derived distance and torsion angle restraints along with 307 ambiguous distance restraints. Figure 1A
depicts a backbone (N,C
,C) superposition of 10 low-energy structures that were derived from the NMR data using the program CNX (MSI). Excluding the N-terminal tag the atomic root-mean-squared-deviation (RMSD) about the mean position is 0.51 ± 0.06 Å for the backbone atoms and 1.02 ± 0.09 Å for all heavy atoms. There are no dihedral-angle violations greater than 5° and no NOE violations greater than 0.4 Å. Only covalent geometry, NOE, torsion, and repulsive terms were included in the structure refinement. Even so, the Lennard-Jones energy is large and negative (-380 ± 13 kcal mole-1), indicating that the structures have favorable nonbonded contacts. A summary of the structural statistics is given in Table 1 of the supplementary material. Analysis of the average-minimized structures (173) with the program PROCHECK showed that 70% of the residues for UBL5 lie in the most favored region of the Ramachandran plot, while an additional 28.7% lie in allowed regions (Laskowski et al. 1993).
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-helix follows, and this is connected to a third short sheet. The final sheet of the protein runs parallel with the second ß-sheet and antiparallel to the short third sheet. The final ß-sheet of the protein ends at the next to last residue of the protein, tyrosine 72. The C-terminal di-tyrosine residues have the characteristic chemical shifts of residues in a ß-sheet, and have the expected cross-strand NOEs to residues on strands 2 and 3. These data unambiguously indicate that these residues are involved in the final ß-sheet of the protein and are not exposed residues on the surface of the protein. | Discussion |
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Yeast two hybrid has been used to confirm earlier studies that indicated an interaction between UBL5 and CLK4. CLK4 is the most recently identified, and thus most poorly characterized member of the CLK family. These proteins are believed to play a role in phosphorylation of serine and arginine rich non-snRNP splicing proteins (Nayler et al. 1997) and the control of differential splicing, and may also regulate the activity of PTP1B (Moeslein et al. 1999). It remains to be determined whether CLK4 can also phosphorylate PTP1B. The fact that CLK4 appears to be the only member of this protein family that interacts with UBL5 suggests that CLK4 may have a role distinct from that of the other CLKs.
Based on sequence homology it was predicted that UBL5 would be structurally similar to ubiquitin (Friedmann et al. 2001). This is indeed what we have found. In Figure 2
, we show the secondary structure of UBL5 and a sequence alignment with ubiquitin. The secondary structures of the two proteins are identical. The additional C-terminal residues important for conjugation in ubiquitin-like protein modifiers are, however, missing in UBL5. The backbone atom RMSD of residues 170 of ubiquitin (Cornilescu et al. 1998; PDB entry 1d3z
[PDB]
) and 372 of UBL5 is 1.53 Å. A ribbons representation of ubiquitin is shown in Figure 1C
, which can be compared to UBL5 in Figure 1B
. The only notable difference between the two structures is the unstructured C terminus found in ubiquitin that extends beyond the end of the highly structured portion of the protein. These residues of ubiquitin are colored magenta in Figure 1C
. Based on the strong sequence homology between UBL5 and its orthologs we would expect them to have homologous structures. We would also expect the UBL5 homologs to all have the same structured C terminus, which is very different than that found for ubiquitin and its related modifiers (Bayer et al. 1998; Cornilescu et al. 1998; Rao-Naik et al. 1998; Whitby et al. 1998). This is indeed the case for the yeast ortholog of UBL5, HUB1. The overall fold of HUB1 (PDB entry 1m94
[PDB]
) and UBL5 are identical. The backbone RMSD between the two proteins is 1.66 Å.
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In summary, we have presented the tertiary structure of UBL5, and have shown that its overall fold is similar to ubiquitin. If UBL5 behaves like a ubiquitin-like modifier (Jentsch and Pyrowolakis 2000; Dittmar et al. 2002) then its mechanism of protein conjugation should be quite distinct from that of other ubiquitin-like modifiers because the structure, described herein, shows that this protein has neither the unstructured C terminus nor the C-terminal di-glycine motif, which is found for other proteins of this class. The widespread expression of UBL5 in all tissue types suggests that this protein and its orthologs have an important functional role. The data presented here may aid in the elucidation of the conjugation mechanism of this class of protein modifiers.
| Materials and methods |
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Expression and purification for structural studies
The UBL5 protein used for structural studies was expressed in E. coli BL21(DE3) grown on M9 media, and purified using a Ni-NTA affinity chromatography. Uniformly 15N-labeled and uniformly 15N,13C-labeled samples were prepared with media containing either 15NH4Cl or 15NH4Cl plus [U-13C]glucose. NMR samples contained 0.51.0 mM protein in either 90% H2O/10% 2H2O or 100% 2H2O, 50 mM sodium phosphate (pH 5.7), and 2 mM 2H-dithiothreitol.
NMR spectroscopy
All NMR data were acquired at 298 K on a Bruker DRX500 or DRX600 NMR spectrometer. Backbone 1H, 13C, and 15N resonance assignments were achieved with [15N,13C] UBL5 using a suite of triple-resonance experiments (HN(CA)CB, HN(COCA)CB, HNCO, and HN(CA)C (Clore and Gronenborn 1998; Kanelis et al. 2001). The side-chain 1H and 13C NMR signals were assigned from HCCH-TOCSY experiments. NOE distance restraints were obtained from three-dimensional 15N- and 13C-edited NOESY spectra acquired with a mixing time of 80 msec (Ikura et al. 1990).
Structure calculations
UBL5 structures were calculated using a simulated annealing protocol with the program CNX (MSI; Brunger 1992). A square-well potential (FNOE = 50 kcal mole-1) was used to constrain NOE-derived distances. Based on the cross-peak intensities, NOE-derived distance restraints were given upper bounds of 3.0, 4.0, or 5.0 Å. In the refinement stage, additional ambiguous constraints were added, with an upper bound of 6.0 Å, for unassigned cross-peaks that were consistent with the chemical shift table (i.e., error bars of 0.07 ppm for protons, 0.7 ppm for hetero atoms) and the structure. Torsion angle restraints,
and
, were generated from analysis of N, C, C
, and H
chemical shifts using the TALOS program (Cornilescu et al. 1999). A force constant of 200 kcal mole-1 rad-2 was applied to all torsional restraints. Explicit hydrogen bonds were included in
-helices and ß-sheets for residues observed to have slowly exchanging amide protons and having appropriate short range NOEs. The program PROCHECK was employed to analyze the geometric quality of the calculated structures in the ensemble (Laskowski et al. 1993). The average minimized coordinates for UBL5 have been deposited with the Protein Data Bank (RCSB018874; PDB number 1POR).
Yeast two-hybrid analysis
Yeast two-hybrid analysis was performed using the Matchmaker 2 two-hybrid kit (Clontech). Interactions were identified following the manufacturers recommended protocol. The UBL5 gene was cloned in frame with GAL4 in pGBKT7, and expression was verified by Western blot using anti-GAL4 antibody (Clontech). Two hybrid positives were identified by growth on selective LWHA X-Gal-containing media only in the presence of pGBKT7UBL5 and not pGBKT7 alone.
| Electronic supplemental material |
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| Acknowledgments |
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The publication costs of this article were defrayed in part by payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 USC section 1734 solely to indicate this fact.
| References |
|---|
|
|
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Brunger, A.T. 1992. X-PLOR version 3.1. Yale University Press, New Haven, CT.
Carson, M. 1987. Ribbons. J. Mol. Graph. 5: 103106.
Clore, G.M. and Gronenborn, A.M. 1998. NMR structure determination of proteins and protein complexes larger than 20 kDa. Curr. Opin. Chem. Biol. 2: 564570.[CrossRef][Medline]
Collier, G.R., McMillan, J.S., Windmill, K., Walder, K., Tenne-Brown, J., de Silva, A., Trevaskis, J., Jones, S., Morton, G.J., Lee, S., et al. 2000. BeaconA novel gene involved in the regulation of energy balance. Diabetes 49: 17661771.[Abstract]
Cornilescu, G., Delaglio, F., and Bax, A. 1999. Protein backbone angle restraints from searching a database for chemical shift and sequence homology. J. Biomol. NMR 13: 289302.[CrossRef][Medline]
Cornilescu, G., Marquardt, J.L., Ottiger, M., and Bax, A. 1998. Validation of protein structure from anisotropic carbonyl chemical shifts in a dilute liquid crystalline phase. J. Am. Chem. Soc. 120: 68366837.[CrossRef]
Dittmar, G.A.G., Wilkinson, C.R.M., Jedrzejewski, P.T., and Finley, D. 2002. Role of a ubiquitin-like modification in polarized morphogenesis. Science 295: 24422446.
Friedmann, J.S., Koop, B.F., Raymond, V., and Walter, M.A. 2001. Isolation of a ubiquitin-like (UBL5) gene from a screen identifying highly expressed and conserved iris genes. Genomics 71: 252255.[CrossRef][Medline]
Glickman, M.H. and Ciechanover, A. 2002. The ubiquitin-proteasome proteolytic pathway: Destruction for the sake of construction. Physiol. Rev. 82: 373428.
Hochstrasser, M. 1996. Ubiquitin-dependent protein degradation. Annu. Rev. Genet. 30: 405439.[CrossRef][Medline]
Ikura, M., Kay, L.E., Tschudin, R., and Bax, A. 1990. Three-dimensional NOESY-HMQC spectroscopy of a 13C-labeled protein. J. Magn. Reson. 86: 204209.
Jentsch, S. and Pyrowolakis, G. 2000. Ubiquitin and its kin: How close are the family ties? Trends Cell Biol. 10: 335342.[CrossRef][Medline]
Kanelis, V., Forman-Kay, J.D., and Kay, L.E. 2001. Multidimensional NMR methods for protein structure determination. IUBMB Life 52: 291302.[Medline]
Laskowski, R.A., MacArthur, M.W., Moss, D.S., and Thornton, J.M. 1993. Procheck. J. Appl. Crystallogr. 26: 283291.[CrossRef]
Menegay, H.J., Myers, M.P., Moeslein, F.M., and Landreth, G.E. 2000. Biochemical characterization and localization of the dual specificity kinase CLK1. J. Cell Sci. 113: 32413253.[Abstract]
Moeslein, F.M., Myers, M.P., and Landreth, G.E. 1999. The CLK family kinases, CLK1 and CLK2, phosphorylate and activate the tyrosine phosphatase, PTP-1B. J. Biol. Chem. 274: 2669726704.
Nayler, O., Stamm, S., and Ullrich, A. 1997. Characterization and comparison of four serine- and arginine-rich (sr) protein kinases. Biochem. J. 326: 693700.
Rao-Naik, C., delaCruz, W., Laplaza, J.M., Tan, S., Callis, J., and Fisher, A.J. 1998. The rub family of ubiquitin-like proteinsCrystal structure of arabidopsis Rub1 and expression of multiple rubs in arabidopsis. J. Biol. Chem. 273: 3497634982.
Schultz, J., Jones, T., Bork, P., Sheer, D., Blencke, S., Steyrer, S., Wellbrock, U., Bevec, D., Ullrich, A., and Wallasch, C. 2001. Molecular characterization of a cDNA encoding functional human CLK4 kinase and localization to chromosome 4q35. Genomics 71: 368370.[CrossRef][Medline]
Whitby, F.G., Xia, G., Pickart, C.M., and Hill, C.P. 1998. Crystal structure of the human ubiquitin-like protein NEDD8 and interactions with ubiquitin pathway enzymes. J. Biol. Chem. 273: 3498334991.
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