Phox homology

Fig. 1. Structure of class I and class II PI3Ks and their substrate specificity. PRR, proline-rich regions PX, phox homology domain.

PX PhoX homologous domain, present in p47phox and p40phox E(MFP) 14(14) 10(10) ... 

Members of the PLD superfamily that exhibit PLD activity contain four conserved sequences (I—IV) of which sequences I and IV contain the HKD motifs [4] (Fig. 4.1). The functions of sequences I and III have not been defined, but it is assumed they participate in catalysis. Two adjacent domains, PX (Phox homology) and PH (pleckstrin homology), are located in the N-terminal sequences of mammalian, yeast and nematode PLDs and in the plant PLD C isozymes, but are absent from bacterial and most plant enzymes [5, 6]. The plant PLDs lacking the PX/PH tandem domain contain a Ca /phospholipid binding domain, designated C2, at the N-terminus and require Ca for activity [6]. 

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