InterPro: IPR002433 Ornithine decarboxylase

These enzymes are collectively known as group IV decarboxylases [1]. Pyridoxal-dependent decarboxylases acting on ornithine, lysine, arginine and related substrates can be classified into two different families on the basis of sequence similarities [2, 1]. Members of this family while most probably evolutionary related, do not share extensive regions of sequence similarities. The proteins contain a conserved lysine residue which is known, in mouse ODC [3], to be the site of attachment of the pyridoxal-phosphate group. The proteins also contain a stretch of three consecutive glycine residues and has been proposed to be part of a substrate- binding region [4].

The ornithine decarboxylases catalyse the transformation of ornithine into putrescine. Phylogenetic analysis of the mRNAs from several mammalian species suggests that ODC is encoded by orthologous genes in the different species. Analysis of divergence patterns in a number of subregions showed that the domains have evolved in a noncoordinate fashion. Evolution of each subregion has been episodic, with periods of both rapid and slow divergence, possibly indicating the existence of selection pressures that were exerted in a time- and domain-specific manner during mammalian speciation. The active form of mammalian ODC is a homodimer of 53 kDa subunits (the monomer retains no enzymatic activity). In vitro hybridisation and cross- linkage analysis have suggested that the active site of ODC is formed at the interface of the two monomers via the interaction of the cysteine-360- containing region of one subunit with the lysine-69-containing region of the other [3].