Kovacev J, Wu K, Spratt DE, Chong RA, Lee C, Nayak J, Shaw GS, Pan ZQ

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 (SCF-βTrCP) E3 ubiquitin (Ub) ligase complex. Competition experiments revealed that SCF-βTrCP formed a complex with IκBα and that the Nedd8 modified E3-substrate platform engaged in dynamic interactions with ...

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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 K48-Ub chain of a length greater than four, but not its K63 linkage counterparts, slowed the rate of additional Ub conjugation. Thus, the Ub chain length and linkage impact kinetic rates of chain elongation. Given that K48-tetra-Ub is packed into compact conformations due to extensive intra-chain interactions between Ub subunits, this topology may limit the accessibility of SCF-βTrCP/Cdc34 to K48 of the distal Ub and result in slowed elongation.

Date: Jan. 24, 2014

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