title: Mutational analysis of the antizyme-binding element reveals critical residues for the function of ornithine decarboxylase.
abstract: BACKGROUND
  Ornithine decarboxylase (ODC), the key enzyme in the polyamine biosynthetic pathway, is highly regulated by antizymes (AZs), small proteins that bind and inhibit ODC and increase its proteasomal degradation. Early studies delimited the putative AZ-binding element (AZBE) to the region 117-140 of ODC. The aim of the present work was to study the importance of certain residues of the region 110-142 that includes the AZBE region for the interaction between ODC and AZ1 and the ODC functionality.
  
  
  METHODS
  Computational analysis of the protein sequences of the extended AZBE site of ODC and ODC paralogues from different eukaryotes was used to search for conserved residues. The influence of these residues on ODC functionality was studied by site directed mutagenesis, followed by different biochemical techniques.
  
  
  RESULTS
  The results revealed that: a) there are five conserved residues in ODC and its paralogues: K115, A123, E138, L139 and K141; b) among these, L139 is the most critical one for the interaction with AZs, since its substitution decreases the affinity of the mutant protein towards AZs; c) all these conserved residues, with the exception of A123, are critical for ODC activity; d) substitutions of K115, E138 or L139 diminish the formation of ODC homodimers.
  
  
  CONCLUSIONS
  These results reveal that four of the invariant residues of the AZBE region are strongly related to ODC functionality.
  
  
  CONCLUSIONS
  This work helps to understand the interaction between ODC and AZ1, and describes various new residues involved in ODC activity, a key enzyme for cell growth and proliferation.
authors.affiliation: Department of Biochemistry and Molecular Biology B and Immunology, Faculty of Medicine, University of Murcia, Spain.
authors.forename: Bruno
authors.initials: B
authors.lastname: Ramos-Molina
authors.forename: Ana
authors.initials: A
authors.lastname: Lambertos
authors.forename: Andrés J
authors.initials: AJ
authors.lastname: López-Contreras
authors.forename: Rafael
authors.initials: R
authors.lastname: Peñafiel
mesh_terms: D000595:Amino Acid Sequence; D001665:Binding Sites; D002460:Cell Line; D004252:DNA Mutational Analysis / Q000379:methods; D057809:HEK293 Cells; D006801:Humans; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D050505:Mutant Proteins / Q000235:genetics / Q000378:metabolism; D009955:Ornithine Decarboxylase / Q000235:genetics* / Q000378:metabolism; D011485:Protein Binding; D011487:Protein Conformation; D011506:Proteins / Q000235:genetics* / Q000378:metabolism
chemical_list: D050505:Mutant Proteins; D011506:Proteins; C031017:ornithine decarboxylase antizyme; D009955:Ornithine Decarboxylase
keywords: AZ; AZBE; AZIN; Antizyme; Antizyme-binding element; DFMO; HA; HEK; ODC; Ornithine decarboxylase; PLP; Polyamines; Protein–protein interaction; antizyme; antizyme inhibitor; antizyme-binding element; hemagglutinin; human embryonic kidney; ornithine decarboxylase; pyridoxal phosphate; α-difluoromethylornithine