PX domain takes shape.

In recent years, a number of protein domains have been identified that bind phosphoinositides and direct proteins to membrane targets. A recent addition to this group is the Phox homology or PX domain, a 120-amino acid domain conserved from yeast to humans, which is present in proteins involved in cell signaling, protein sorting, vesicle fusion, and the assembly of components of the superoxide generating system of neutrophils. These domains have varying affinities for phosphatidylinositol-3-phosphate (PI(3)P), and PI(3,4) and (4,5) bisphosphates, which couple the PI kinase and phosphatase signaling networks to the assembly of proteins at membrane surfaces. These PX domains also contain a PXXP motif, allowing them to bind to proteins containing Src homology 3 (SH3) domains.