Pleckstrin homology domain (PH domain) or (PHIP) is a protein domain of approximately 120 amino acids that occurs in a wide range of proteins involved in intracellular signaling or as constituents of the cytoskeleton.[1][2][3][4][5][6][7]
Individual PH domains possess specificities for phosphoinositides phosphorylated at different sites within the inositol ring, e.g., some bind phosphatidylinositol (4,5)-bisphosphate but not phosphatidylinositol (3,4,5)-trisphosphate or phosphatidylinositol (3,4)-bisphosphate, while others may possess the requisite affinity. This is important because it makes the recruitment of different PH domain containing proteins sensitive to the activities of enzymes that either phosphorylate or dephosphorylate these sites on the inositol ring, such as phosphoinositide 3-kinase or PTEN, respectively. Thus, such enzymes exert a part of their effect on cell function by modulating the localization of downstream signaling proteins that possess PH domains that are capable of binding their phospholipid products.
Structure
The 3D structure of several PH domains has been determined.[11] All known cases have a common structure consisting of two perpendicular anti-parallel beta sheets, followed by a C-terminalamphipathic helix. The loops connecting the beta-strands differ greatly in length, making the PH domain relatively difficult to detect while providing the source of the domain's specificity. The only conserved residue among PH domains is a single tryptophan located within the alpha helix that serves to nucleate the core of the domain.
Proteins containing PH domain
PH domains can be found in many different proteins, such as OSBP or ARF. Recruitment to the Golgi apparatus in this case is dependent on both PtdIns and ARF. A large number of PH domains have poor affinity for phosphoinositides and are hypothesized to function as protein binding domains. A Genome-wide look in Saccharomyces cerevisiae showed that most of the 33 yeast PH domains are indeed promiscuous in binding to phosphoinositides, while only one (Num1-PH) behaved highly specific .[12] Proteins reported to contain PH domains belong to the following families:
Pleckstrin, the protein where this domain was first detected, is the major substrate of protein kinase C in platelets. Pleckstrin contains two PH domains. ARAP proteins contain five PH domains.
^Musacchio A, Gibson T, Rice P, Thompson J, Saraste M (September 1993). "The PH domain: a common piece in the structural patchwork of signalling proteins". Trends in Biochemical Sciences. 18 (9): 343–8. doi:10.1016/0968-0004(93)90071-T. PMID8236453.
^Ingley E, Hemmings BA (December 1994). "Pleckstrin homology (PH) domains in signal transduction". Journal of Cellular Biochemistry. 56 (4): 436–43. doi:10.1002/jcb.240560403. PMID7890802. S2CID23154429.
^Saraste M, Hyvönen M (June 1995). "Pleckstrin homology domains: a fact file". Current Opinion in Structural Biology. 5 (3): 403–8. doi:10.1016/0959-440X(95)80104-9. PMID7583640.
^Wang DS, Shaw G (December 1995). "The association of the C-terminal region of beta I sigma II spectrin to brain membranes is mediated by a PH domain, does not require membrane proteins, and coincides with a inositol-1,4,5 triphosphate binding site". Biochemical and Biophysical Research Communications. 217 (2): 608–15. doi:10.1006/bbrc.1995.2818. PMID7503742.
^Wang DS, Shaw R, Winkelmann JC, Shaw G (August 1994). "Binding of PH domains of beta-adrenergic receptor kinase and beta-spectrin to WD40/beta-transducin repeat containing regions of the beta-subunit of trimeric G-proteins". Biochemical and Biophysical Research Communications. 203 (1): 29–35. doi:10.1006/bbrc.1994.2144. PMID8074669.
