Site-2 Protease Substrate Specificity and Coupling in Trans by a PDZ-substrate Adapter Protein

Proc Natl Acad Sci U S A. 2013 Nov 26;110(48):19543-8. doi: 10.1073/pnas.1305934110. Epub 2013 Nov 11.


Site-2 proteases (S2Ps) are intramembrane metalloproteases that cleave transmembrane substrates in all domains of life. Many S2Ps, including human S2P and Mycobacterium tuberculosis Rip1, have multiple substrates in vivo, which are often transcriptional regulators. However, S2Ps will also cleave transmembrane sequences of nonsubstrate proteins, suggesting additional specificity determinants. Many S2Ps also contain a PDZ domain, the function of which is poorly understood. Here, we identify an M. tuberculosis protein, PDZ-interacting protease regulator 1 (Ppr1), which bridges between the Rip1 PDZ domain and anti-sigma factor M (Anti-SigM), a Rip1 substrate, but not Anti-SigK or Anti-SigL, also Rip1 substrates. In vivo analyses of Ppr1 function indicate that it prevents nonspecific activation of the Rip1 pathway while coupling Rip1 cleavage of Anti-SigM, but not Anti-SigL, to site-1 proteolysis. Our results support a model of S2P substrate specificity in which a substrate-specific adapter protein tethers the S2P to its substrate while holding the protease inactive through its PDZ domain.

Keywords: Sigma factor; Tuberculosis; intramembrane proteolysis; signal transduction.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Bacterial Proteins / metabolism*
  • Metalloproteases / metabolism*
  • Mice
  • Models, Biological*
  • Mycobacterium tuberculosis / enzymology*
  • PDZ Domains / physiology
  • Real-Time Polymerase Chain Reaction
  • Sigma Factor / antagonists & inhibitors
  • Signal Transduction / physiology*
  • Substrate Specificity
  • Two-Hybrid System Techniques
  • Yeasts


  • Bacterial Proteins
  • Sigma Factor
  • Metalloproteases