Determinants of proteasome recognition of ornithine decarboxylase, a ubiquitin-independent substrate

• Published in: The EMBO journal Vol. 22; no. 7; pp. 1488 - 1496
• Main Authors: Zhang, Mingsheng, Pickart, Cecile M., Coffino, Philip
• Format: Journal Article
• Language: English
• Published: Chichester, UK John Wiley & Sons, Ltd 01.04.2003; Blackwell Publishing Ltd; Oxford University Press
• Subjects: Amino acids; Animals; antizyme; Cysteine Endopeptidases - metabolism; Humans; Mice; Multienzyme Complexes - metabolism; ornithine decarboxylase; Ornithine Decarboxylase - metabolism; proteasome; Proteasome Endopeptidase Complex; protein degradation; Rats; Rats, Sprague-Dawley; Substrate Specificity; Tetrahydrofolate Dehydrogenase - metabolism; ubiquitin; Ubiquitin - metabolism
• ISSN: 0261-4189; 1460-2075; 1460-2075
• DOI: 10.1093/emboj/cdg158

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.