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Open Access

Allosteric regulation of E2:E3 interactions promote a processive ubiquitination machine

Ranabir Das, Yu‐He Liang, Jennifer Mariano, Jess Li, Tao Huang, Aaren King, Sergey G Tarasov, Allan M Weissman, Xinhua Ji, R Andrew Byrd

Author Affiliations

  1. Ranabir Das1,
  2. Yu‐He Liang2,
  3. Jennifer Mariano3,
  4. Jess Li1,
  5. Tao Huang1,
  6. Aaren King1,
  7. Sergey G Tarasov1,
  8. Allan M Weissman3,
  9. Xinhua Ji2 and
  10. R Andrew Byrd*,1
  1. 1 Structural Biophysics Laboratory, Center for Cancer Research, National Cancer Institute, Frederick, MD, USA
  2. 2 Macromolecular Crystallography Laboratory, Center for Cancer Research, National Cancer Institute, Frederick, MD, USA
  3. 3 Laboratory of Protein Dynamics and Signaling, Center for Cancer Research, National Cancer Institute, Frederick, MD, USA
  1. *Corresponding author. Structural Biophysics Laboratory, Center for Cancer Research, National Cancer Institute, PO Box B, Building 538, Frederick, MD 21702‐1201, USA. Tel.:+1 301 846 1407; Fax:+1 301 846 6231; E-mail: byrdra{at}mail.nih.gov

Abstract

RING finger proteins constitute the large majority of ubiquitin ligases (E3s) and function by interacting with ubiquitin‐conjugating enzymes (E2s) charged with ubiquitin. How low‐affinity RING–E2 interactions result in highly processive substrate ubiquitination is largely unknown. The RING E3, gp78, represents an excellent model to study this process. gp78 includes a high‐affinity secondary binding region for its cognate E2, Ube2g2, the G2BR. The G2BR allosterically enhances RING:Ube2g2 binding and ubiquitination. Structural analysis of the RING:Ube2g2:G2BR complex reveals that a G2BR‐induced conformational effect at the RING:Ube2g2 interface is necessary for enhanced binding of RING to Ube2g2 or Ube2g2 conjugated to Ub. This conformational effect and a key ternary interaction with conjugated ubiquitin are required for ubiquitin transfer. Moreover, RING:Ube2g2 binding induces a second allosteric effect, disrupting Ube2g2:G2BR contacts, decreasing affinity and facilitating E2 exchange. Thus, gp78 is a ubiquitination machine where multiple E2‐binding sites coordinately facilitate processive ubiquitination.

  • Received May 13, 2013.
  • Accepted July 12, 2013.

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