A SnapShot of Ubiquitin Chain Elongation: LYSINE 48-TETRA-UBIQUITIN SLOWS DOWN UBIQUITINATION* |
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| Authors: | Jordan Kovacev Kenneth Wu Donald E Spratt Robert A Chong Chan Lee Jaladhi Nayak Gary S Shaw Zhen-Qiang Pan |
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| Institution: | From the ‡Department of Oncological Sciences, The Icahn School of Medicine at Mount Sinai, One Gustave L. Levy Place, New York, New York 10029-6574.;§Department of Biochemistry, Schulich School of Medicine and Dentistry, University of Western Ontario, London, Ontario N6A 5C1, Canada, and ;¶Xuzhou Medical College, Jiangsu Key Laboratory of Biological Cancer Therapy, Jiangsu 221002, China |
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| Abstract: | We have explored the mechanisms of polyubiquitin chain assembly with reconstituted ubiquitination of IκBα and β-catenin by the Skp1-cullin 1-βTrCP F-box protein (SCFβTrCP) E3 ubiquitin (Ub) ligase complex. Competition experiments revealed that SCFβTrCP formed a complex with IκBα and that the Nedd8 modified E3-substrate platform engaged in dynamic interactions with the Cdc34 E2 Ub conjugating enzyme for chain elongation. Using “elongation intermediates” containing β-catenin linked with Ub chains of defined length, it was observed that a Lys-48-Ub chain of a length greater than four, but not its Lys-63 linkage counterparts, slowed the rate of additional Ub conjugation. Thus, the Ub chain length and linkage impact kinetic rates of chain elongation. Given that Lys-48-tetra-Ub is packed into compact conformations due to extensive intrachain interactions between Ub subunits, this topology may limit the accessibility of SCFβTrCP/Cdc34 to the distal Ub Lys-48 and result in slowed elongation. |
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| Keywords: | Catenin E3 Ubiquitin Ligase Enzymes Post Translational Modification Protein Degradation Ubiquitination Cdc34 E2 Conjugating Enzyme SCF UbcH5c |
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