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Prokaryotic ubiquitin-like protein pup is intrinsically disordered

Xiang Chen1, William C Solomon, Yang Kang

  • 1Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota, Minneapolis, 55455, USA.

Journal of Molecular Biology
|July 18, 2009
PubMed

Insights

The prokaryotic ubiquitin-like protein Pup, unlike ubiquitin, is intrinsically disordered. Pup binds tightly to Mpa, revealing insights into its role in protein degradation signaling.

Area of Science:

  • Biochemistry
  • Molecular Biology
  • Structural Biology

Background:

  • The prokaryotic ubiquitin-like protein Pup signals substrates for degradation by the Mycobacterium tuberculosis proteasome via Mpa.
  • Ubiquitin, a eukaryotic protein, forms polymers to signal proteasomal degradation and has diverse functions due to its stable structure.

Purpose of the Study:

  • To investigate the structural properties of Pup and its interaction with Mpa.
  • To elucidate the mechanism of Pup's function as a degradation signal.

Main Methods:

  • Nuclear Magnetic Resonance (NMR) spectroscopy was employed to study Pup and its interaction with Mpa.
  • Titration experiments were performed to analyze binding kinetics and affinity.

Main Results:

  • Pup is intrinsically disordered, differing from the structured ubiquitin.
  • The Pup:Mpa interaction involves a large contact surface (S21-K61) and exhibits slow exchange kinetics, indicating high affinity.
  • Transient intermediate states of Pup were observed during binding, and Mpa selected a specific conformation for a flexible region of Pup.

Conclusions:

  • Pup's disordered nature is crucial for its function as a degradation signal.
  • The high-affinity interaction with Mpa, involving specific conformational selection, provides mechanistic insights into Pup-mediated proteasomal targeting.

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