Proteolytic activity of HtpX, a membrane-bound and stress-controlled protease from Escherichia coli

J Biol Chem. 2005 Sep 30;280(39):33305-10. doi: 10.1074/jbc.M506180200. Epub 2005 Aug 2.


Escherichia coli HtpX is a putative membrane-bound zinc metalloprotease that has been suggested to participate in the proteolytic quality control of membrane proteins in conjunction with FtsH, a membrane-bound and ATP-dependent protease. Here, we biochemically characterized HtpX and confirmed its proteolytic activities against membrane and soluble proteins. HtpX underwent self-degradation upon cell disruption or membrane solubilization. Consequently, we purified HtpX under denaturing conditions and then refolded it in the presence of a zinc chelator. When supplemented with Zn2+, the purified enzyme exhibited self-cleavage activity. In the presence of zinc, it also degraded casein and cleaved a solubilized membrane protein, SecY. We verified its ability to cleave SecY in vivo by overproducing both HtpX and SecY. These results showed that HtpX is a zinc-dependent endoprotease member of the membrane-localized proteolytic system in E. coli.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adenosine Triphosphate / metabolism
  • Bacterial Proteins / metabolism*
  • Caseins / metabolism
  • Chelating Agents / pharmacology
  • Endopeptidases / metabolism*
  • Escherichia coli / enzymology*
  • Escherichia coli / growth & development
  • Escherichia coli Proteins / isolation & purification
  • Escherichia coli Proteins / metabolism*
  • Heat-Shock Proteins / isolation & purification
  • Heat-Shock Proteins / metabolism*
  • Immunoblotting
  • Membrane Proteins / metabolism*
  • Metalloproteases
  • Precipitin Tests
  • Protein Denaturation
  • Protein Renaturation / drug effects
  • SEC Translocation Channels
  • Zinc / metabolism
  • Zinc / pharmacology


  • Bacterial Proteins
  • Caseins
  • Chelating Agents
  • Escherichia coli Proteins
  • Heat-Shock Proteins
  • Membrane Proteins
  • SEC Translocation Channels
  • SecY protein, E coli
  • HtpX protein, E coli
  • Adenosine Triphosphate
  • Endopeptidases
  • Metalloproteases
  • Zinc