title: Adult human liver contains intermediate-type proteasomes with different enzymatic properties.
abstract: BACKGROUND
  The 20S proteasome is the proteolytic core of the major intracellular protein degradative system, the ubiquitin-proteasome system. Since little is known about proteasomes of human liver, we have investigated the proteasome spectrum in adult human liver.
  
  
  METHODS
  20S proteasomes were chromatographically purified from adult human liver and from HuH7 cells. They were divided into subpopulations and subtypes and characterized with regard to their proteolytic activities using short fluorogenic oligo- and long poly-peptide substrates. Their subunit composition was studied by immunoblotting.
  
  
  RESULTS
  Proteasomes from adult human liver tissue can be separated into three subpopulations (I, II, III), each of which is composed of several subtypes, which total to a spectrum of 14 different subtypes. Two minor subtypes contain only the immuno-subunits β1i and β5i but not their standard counterparts; all others are intermediate subtypes containing β1 and β5 standard- and β1i and β5i immuno-subunits in various compositions. With regard to the proteolytic activities we observed that a decreasing content of subunit β1i in the subtypes goes along with a decreasing ratio of chymotrypsin-like/caspase-like activity, whereas the degradation rate of a 30 mer polypeptide substrate increased with decreasing β1i content. By comparison, 20S proteasomes from HuH7 cells do not contain immuno-subunits but are pure standard proteasomes, which can be separated into three subtypes.
  
  
  CONCLUSIONS
  These findings suggest that adult human liver contains a spectrum of 14 different 20S proteasome subtypes with different enzymatic properties reflecting most probably an adaptive response of liver cell functions to challenging factors during lifetime.
authors.affiliation: Charité-Universitätsmedizin Berlin, Institut für Biochemie, Berlin, Germany.
authors.forename: Sabrina
authors.initials: S
authors.lastname: Gohlke
authors.affiliation: Charité-Universitätsmedizin Berlin, Institut für Biochemie, Berlin, Germany.
authors.forename: Alexander
authors.initials: A
authors.lastname: Kloss
authors.affiliation: Charité-Universitätsmedizin Berlin, Institut für Rechtsmedizin, Berlin, Germany.
authors.forename: Michael
authors.initials: M
authors.lastname: Tsokos
authors.affiliation: Charité-Universitätsmedizin Berlin, Institut für Biochemie, Berlin, Germany.
authors.forename: Kathrin
authors.initials: K
authors.lastname: Textoris-Taube
authors.affiliation: Charité-Universitätsmedizin Berlin, Institut für Biochemie, Berlin, Germany.
authors.forename: Christin
authors.initials: C
authors.lastname: Keller
authors.affiliation: Charité-Universitätsmedizin Berlin, Institut für Biochemie, Berlin, Germany.
authors.forename: Peter-Michael
authors.initials: PM
authors.lastname: Kloetzel
authors.affiliation: Charité-Universitätsmedizin Berlin, Institut für Biochemie, Berlin, Germany.
authors.forename: Burkhardt
authors.initials: B
authors.lastname: Dahlmann
mesh_terms: D002460:Cell Line; D004586:Electrophoresis; D004912:Erythrocytes / Q000201:enzymology*; D006801:Humans; D008099:Liver / Q000201:enzymology*; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism*; D013154:Spleen / Q000201:enzymology*
chemical_list: D046988:Proteasome Endopeptidase Complex