CRYSTAL-STRUCTURE OF A PURPLE ACID-PHOSPHATASE CONTAINING A DINUCLEARFE(III)-ZN(II) ACTIVE-SITE

Kidney bean purple acid phosphatase (KBPAP) is an Fe(III)-Zn(II) metal loenzyme resembling the mammalian Fe(III)-Fe(II) purple acid phosphata ses. The structure of the homodimeric III-kilodalton KBPAP was determi ned at a resolution of 2.9 angstroms. The enzyme contains two domains in each subunit. The active site is located in the carboxyl-terminal t erminal domain at the carboxy end of two sandwiched beta alpha beta al pha beta motifs. The two metal ions are 3.1 angstroms apart and bridge d monodentately by Asp(164) The iron is further coordinated by Tyr(167 ), His(325), and Asp(135), and the zinc by His(286), His(323), and Asn (201). The active-site structure is consistent with previous proposals regarding the mechanism of phosphate ester hydrolysis involving nucle ophilic attack on the phosphate group by an Fe(III)coordinated hydroxi de ion.