title: Determinants of proteasome recognition of ornithine decarboxylase, a ubiquitin-independent substrate.
abstract: Ornithine decarboxylase (ODC) is regulated by its metabolic products through a feedback loop that employs a second protein, antizyme 1 (AZ1). AZ1 accelerates the degradation of ODC by the proteasome. We used purified components to study the structural elements required for proteasomal recognition of this ubiquitin-independent substrate. Our results demonstrate that AZ1 acts on ODC to enhance the association of ODC with the proteasome, not the rate of its processing. Substrate-linked or free polyubiquitin chains compete for AZ1-stimulated degradation of ODC. ODC-AZ1 is therefore recognized by the same element(s) in the proteasome that mediate recognition of polyubiquitin chains. The 37 C-terminal amino acids of ODC harbor an AZ1-modulated recognition determinant. Within the ODC C terminus, three subsites are functionally distinguishable. The five terminal amino acids (ARINV, residues 457-461) collaborate with residue C441 to constitute one recognition element, and AZ1 collaborates with additional constituents of the ODC C terminus to generate a second recognition element.
authors.affiliation: Department of Microbiology and Immunology, University of California, San Francisco, CA 94143, USA.
authors.forename: Mingsheng
authors.initials: M
authors.lastname: Zhang
authors.forename: Cecile M
authors.initials: CM
authors.lastname: Pickart
authors.forename: Philip
authors.initials: P
authors.lastname: Coffino
mesh_terms: D000818:Animals; D003546:Cysteine Endopeptidases / Q000378:metabolism*; D006801:Humans; D051379:Mice; D009097:Multienzyme Complexes / Q000378:metabolism*; D009955:Ornithine Decarboxylase / Q000378:metabolism*; D046988:Proteasome Endopeptidase Complex; D051381:Rats; D017207:Rats, Sprague-Dawley; D013379:Substrate Specificity; D013762:Tetrahydrofolate Dehydrogenase / Q000378:metabolism; D025801:Ubiquitin / Q000378:metabolism*
chemical_list: D009097:Multienzyme Complexes; D025801:Ubiquitin; D013762:Tetrahydrofolate Dehydrogenase; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex; D009955:Ornithine Decarboxylase