Ke. Tobias et al., GLY387 OF MURINE ORNITHINE DECARBOXYLASE IS ESSENTIAL FOR THE FORMATION OF STABLE HOMODIMERS, European journal of biochemistry, 218(1), 1993, pp. 245-250
In its active form mammalian ornithine decarboxylase (ODC) is a homodi
mer composed of two 53-kDa subunits while the monomer retains no enzym
ic activity. In the present study we demonstrate that Gly387 of mouse
ODC plays an important role in enabling dimer formation. Gly387 of mou
se ODC, an evolutionary conserved residue, was converted to all possib
le 19 amino acids using site-directed mutagenesis. With the exception
of alanine, all other substitutions of Gly387 completely abolished enz
ymic activity. Cross-linking analysis and fractionation through a Supe
rose-12 sizing column have demonstrated that mutant subunits are detec
ted only in their monomeric form. These results strongly suggest that
the primary lesion of substitution at position 387 of mouse ODC is the
inability of mutant subunits to associate with each other to form the
active homodimers. In agreement with this conclusion, G387 A, the onl
y mutant that retained partial activity, displayed reduced dimerizatio
n. The degradation rate of ODC mutants in which Gly387 was substituted
by aspartic acid or alanine was enhanced compared to the wild-type en
zyme, suggesting that monomers may be more susceptible to degradation.