Ornithine decarboxylase antizyme (ODC-Az) is a small (142 aa) regulatory protein and the master negative regulator of cellular polyamine homeostasis. It binds to monomers of ornithine decarboxylase (ODC), the rate-limiting enzyme of polyamine biosynthesis, sterically preventing assembly of the catalytically active ODC homodimer and thereby inhibiting ODC enzymatic activity. In addition to inhibiting ODC, antizyme targets the bound ODC monomer for ubiquitin-independent degradation by the 26S proteasome, providing a second, irreversible layer of down-regulation. Through these activities antizyme lowers intracellular putrescine, spermidine and spermine levels and also suppresses cellular polyamine uptake, coupling polyamine biosynthesis and transport to feedback control. Antizyme synthesis is itself controlled by an autoregulatory, polyamine-stimulated +1 ribosomal frameshifting event required to translate the full-length protein from two overlapping open reading frames, so that high polyamine levels increase antizyme production and thereby reinforce the negative feedback loop. The protein acts predominantly in the cytoplasm but can also localize to the nucleus. This regulatory mechanism is deeply conserved across eukaryotes, from yeast to nematodes to mammals.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0005634 nucleus | IBA GO_REF:0000033 | KEEP AS NON CORE | Summary: Nuclear localization is inferred by phylogenetic propagation from the antizyme ortholog family (PANTHER PTN001616256), where mammalian antizymes have been observed to shuttle between cytoplasm and nucleus. This is a plausible but peripheral localization for the P. pacificus protein; the defining, growth-regulatory action of antizyme (ODC binding, inhibition and proteasomal targeting) occurs predominantly in the cytoplasm. Retained as a valid but non-core cellular component. |
| GO:0005737 cytoplasm | IBA GO_REF:0000033 | KEEP AS NON CORE | Summary: Cytoplasm is the principal site where antizyme binds ODC monomers, inhibits ODC activity and delivers ODC to the 26S proteasome, consistent with the well-established antizyme ortholog family. The localization is correct, but "cytoplasm" is a broad cellular-component term that does not itself describe the molecular function; retained as a valid non-core location. |
| GO:0008073 ornithine decarboxylase inhibitor activity | IBA GO_REF:0000033 | ACCEPT | Summary: This is the core molecular function of antizyme and is strongly supported. The annotation is propagated phylogenetically from an antizyme ortholog family with direct experimental evidence (e.g. human and mouse antizymes, UniProtKB:P54368, O95190, Q9UMX2). The P. pacificus protein belongs to the ODC antizyme family (Pfam PF02100, InterPro IPR002993) and is documented to negatively regulate ODC and polyamine biosynthesis, including the conserved polyamine-induced ribosomal frameshifting that controls its own expression. Accept as the central function of this gene. |
| GO:0008073 ornithine decarboxylase inhibitor activity | IEA GO_REF:0000002 | ACCEPT | Summary: Electronic InterPro2GO annotation assigning the same core molecular function based on the diagnostic ODC antizyme domain (InterPro IPR002993 / Pfam PF02100 / PROSITE PS01337) present in this protein. This corroborates the IBA annotation for the same term and is consistent with the antizyme family. Accept as supporting the core function. |
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