<p> Pleckstrin homology (PH) domains are small modular domains that occur once, or occasionally several times, in a large variety of signalling proteins, where they serve as simple targeting domains that recognise only phosphoinositide headgroups [<cite idref="PUB00014130"/>, <cite idref="PUB00014131"/>]. PH domains can target their host protein to the plasma and internal membranes through its association with phosphoinositides. PH domains have a partly opened beta-barrel topology that is capped by an alpha helix. Proteins containing PH domains include pleckstrin (N-terminal), phospholipase C delta-1, beta-spectrin, dynamin, son-of-sevenless, Grp1, Unc-89, Tapp1 and Rac-alpha kinase.</p><p>The structure of PH domains is similar to the phosphotyrosine-binding domain (PTB) found in IRS-1 (insulin receptor substrate 1), Shc adaptor and Numb; to the Ran-binding domain, found in Nup nuclear pore complex and Ranbp1; to the Enabled/VASP homology domain 1 (EVH1 domain), found in Enabled, VASP (vasodilator-stimulated phosphoprotein), Homer and WASP actin regulatory protein; to the third domain of FERM, found in moesin, radixin, ezrin, merlin and talin; and to the PH-like domain of neurobeachin.</p>