The phox homology (PX) domain is a novel protein module containing a conser
ved proline-rich motif, We have shown that the PX domain isolated from the
human p47(phox) protein, a soluble subunit of phagocyte NADPH oxidase, bind
s specifically to the C-terminal SH3 domain derived from the same protein.
The solution structure of p47 PX has an alpha + beta structure with a novel
folding moth topology and reveals that the proline-rich motif is presented
on the molecular surface for easy recognition by the SH3 domain. The proli
ne-rich moth of p47 PX in the free state adopts a distorted left-handed pol
yproline type II helix conformation.