Mutational analysis of the antizyme-binding element reveals critical residues for the function of ornithine decarboxylase

Background: Omithine 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 AZI 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, Al23, E138, L139 and K41; 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 Al23, 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. General significance: 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. (C) 2013 Elsevier B.V. All rights reserved.