Characterisation of the newly identified human Ump1 homologue POMP and analysis of LMP7(β5i) incorporation into 20 S proteasomes

Elke Witt, Daniela Zantopf, Marion Schmidt, Regine Kraft, Peter M. Kloetzel, Elke Krüger

Research output: Contribution to journalArticle

96 Scopus citations

Abstract

Biogenesis of mammalian 20 S proteasomes occurs via precursor complexes containing α and unprocessed β subunits. A human homologue of the yeast proteasome maturation factor Ump1 was identified in 2D gels of 16 S precursor preparations and designated as POMP (proteasome maturation protein). We show that POMP is detected only in precursor fractions and not in fractions containing mature 20 S proteasome. Northern blot experiments revealed that expression of POMP is induced after treatment with interferon γ. To analyse the role of the β5 propeptide for proper maturation and incorporation of the β5 subunit into the complex, human T2 cells, which highly express derivatives of the β5i subunit (LMP7), were studied. In contrast to yeast, the presence of the β5 propeptide is not essential for incorporation of LMP7 into the proteasome complex. Mutated LMP7 subunits either carrying the prosequence of β2i (LMP2) or containing a mutation in the active threonine site are incorporated like wild-type LMP7, while a LMP7 derivative lacking the prosequence completely is incorporated to a lesser extent. Although the absence of the prosequence does not affect incorporation of LMP7, its deletion leads to delayed proteasome maturation and thereby to an accumulation of precursor complexes. As a result of the precursor accumulation, an increased amount of the POMP protein can be detected in these cells. (C) 2000 Academic Press.

Original languageEnglish (US)
Pages (from-to)1-9
Number of pages9
JournalJournal of Molecular Biology
Volume301
Issue number1
DOIs
StatePublished - Aug 4 2000

Keywords

  • 16 S precursor
  • 20 S proteasome
  • ATP-dependent proteolysis
  • LMP7
  • Proteasome maturation factor

ASJC Scopus subject areas

  • Structural Biology
  • Molecular Biology

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