CLONING AND CHARACTERIZATION OF THE NAPA ACID-PHOSPHATASE PHOSPHOTRANSFERASE OF MORGANELLA-MORGANII - IDENTIFICATION OF A NEW FAMILY OF BACTERIAL ACID-PHOSPHATASE-ENCODING GENES

The gene encoding a minor phosphate-irrepressible acid phosphatase (na med NapA) of Morganella morganii was cloned and sequenced, and its pro duct characterized. NapA is a secreted acid phosphatase composed of fo ur 27 kDa polypeptide subunits. The enzyme is active on several organi c phosphate monoesters but not on diesters, and is also endowed with t ransphosphorylating activity from organic phosphoric acid esters to nu cleosides and other compounds with free hydroxyl groups. Its activity is inhibited by EDTA, inorganic phosphate, nucleosides and Ca2+, but n ot by fluoride or tartrate, and is enhanced by Mg2+, Co2+ and Zn2+. At the sequence level, the NapA enzyme did not show similarities to any other sequenced bacterial phosphatases. However, a search for homologo us genes in sequence databases allowed identification of two open read ing frames located within sequenced regions of the Escherichia coli an d Proteus mirabilis genomes respectively, encoding proteins of unknown function which are highly homologous to the Morganella enzyme. Moreov er, the properties of the NapA enzyme are very similar to those report ed for the periplasmic nonspecific acid phosphatase II of Salmonella t yphimurium (for which no sequence data are available). These data poin t to the existence of a new family of bacterial acid phosphatases, whi ch we propose designating class B bacterial acid phosphatases.