Pleckstrin homology (PH) domains form a structurally conserved family that
is associated with many regulatory pathways within the cell. Domains with a
nearly identical fold are found in other families that share no Sequence s
imilarity, suggesting the existence of a stable PH superfold. The PH domain
s generally function as regulated membrane-binding modules that bind to ino
sitol lipids and respond to upstream signals by targeting the host proteins
to the correct cellular sites. The other domains with a similar fold, such
as the phosphotyrosine binding domains, recognize protein ligands.