The Chryseobacterium meningosepticum PafA enzyme: prototype of a new enzyme family of prokaryotic phosphate-irrepressible alkaline phosphatases?

Chryseobacterium meningosepticum is an aerobic Gram-negative rod widely dis tributed in natural environments. Unlike many bacteria, it produces a, phos phate-irrepressible periplasmic alkaline phosphatase (AP). This work descri bes cloning of the gene encoding that enzyme from C meningosepticum CCUG 43 10 (NCTC 10585), and preliminary characterization of its product. The gene, named pafA, encodes a protein (PafA) of 546 amino acids with a calculated molecular mass of the mature peptide of 58682 Da. PafA exhibits high sequen ce identity with the PhoV AP of Synechococcus PCC 7942 (49.9% identity) and with the Cda Call-dependent ATPase of Myroides odoratus (51.9% identity), while being more distantly related to the PhoD AP of Zymomonas mobilis (22. 1% identity) and to the PhoA AP of Escherichia coli (14.0% identity). PafA was partially purified; it exhibits optimal activity at pH 8.5 and is activ e towards a broad spectrum of substrates including both phosphomonoesters a nd ATP, with preferential activity for the latter compound. The present fin dings allow definition of a new family of APs including 60 kDa, periplasmic enzymes whose expression is not influenced by freely available P-i in the medium. Moreover, PafA can be considered an evolutionary intermediate betwe en Ca2+-ATPase of M. odoratus and the APs PhoV of Synechococcus PCC 7942 an d PhoD of Z. mobilis.