Structural relationship between the mammalian Fe(III)-Fe(II) and the Fe(III)-Zn(II) plant purple acid phosphatases

The primary structure of uteroferrin (Uf), a 35 kDa monomeric mammalian purple acid phosphatase (PAP) containing a Fe(III)-Fe(II) center, has been compared with the sequence of the homodimeric 111 kDa Fe(III)-Zn(II) kidney bean purple acid phosphatase (KBPAP). The alignment suggests that the amino acid residues ligating the dimetal center are identical in Uf and KBPAP, although the geometry of the coordination sphere might slightly differ. Secondary structure predictions indicate that Uf contains two beta alpha beta alpha beta motifs thus resembling the folding topology of the plant enzyme. Guided by the recently determined X-ray structure of KBPAP a tentative model for the mammalian PAP can be constructed.