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Characterisation of the newly identified human Ump1 homologue POMP and analysis of LMP7(beta 5i) incorporation into 20 S proteasomes

Item Type:Article
Title:Characterisation of the newly identified human Ump1 homologue POMP and analysis of LMP7(beta 5i) incorporation into 20 S proteasomes
Creators Name:Witt, E. and Zantopf, D. and Schmidt, M. and Kraft, R. and Kloetzel, P.M. and Krueger, E.
Abstract:Biogenesis of mammalian 20 S proteasomes occurs via precursor complexes containing {alpha} and unprocessed {beta}units. 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 {gamma}. To analyse the role of the {beta}5 propeptide for proper maturation and incorporation of the {beta}5 subunit into the complex, human T2 cells, which highly express derivatives of the {beta}subunit (LMP7), were studied. In contrast to yeast, the presence of the {beta}5 propeptide is not essential for incorporation of LMP7 into the proteasome complex. Mutated LMP7 subunits either carrying the prosequence of {beta}2i (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.
Keywords:16 S Precursor, 20 S Proteasome, ATP-Dependent Proteolysis, LMP7, Proteasome Maturation Factor
Source:Journal of Molecular Biology
ISSN:0022-2836
Publisher:Elsevier (The Netherlands)
Volume:301
Number:1
Page Range:1-9
Date:4 August 2000
Official Publication:https://doi.org/10.1006/jmbi.2000.3959
PubMed:View item in PubMed

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