Puratrophin-1 (also called Purkinje cell atrophy-associated protein 1 or PLEKHG4/Pleckstrin homology domain-containing family G member 4) contains a spectrin repeat, a RhoGEF (DH) domain, and a PH domain. It is thought to function in intracellular signaling and cytoskeleton dynamics at the Golgi. Puratrophin-1 is expressed in kidney, Leydig cells in the testis, epithelial cells in the prostate gland and Langerhans islet in the pancreas. A single nucleotide substitution in the puratrophin-1 gene were once thought to result in autosomal dominant cerebellar ataxia (ADCA), but now it has been demonstrated that this ataxia is a result of defects in the BEAN gene. Puratrophin contains a domain architecture similar to that of Dbl family members Dbs and Trio. Dbs is a guanine nucleotide exchange factor (GEF), which contains spectrin repeats, a RhoGEF (DH) domain and a PH domain. The Dbs PH domain participates in binding to both the Cdc42 and RhoA GTPases. Trio plays an essential role in regulating the actin cytoskeleton during axonal guidance and branching. Trio is a multidomain signaling protein that contains two RhoGEF(DH)-PH domains in tandem. PH domains have diverse functions, but in general are involved in targeting proteins to the appropriate cellular location or in the interaction with a binding partner. They share little sequence conservation, but all have a common fold, which is electrostatically polarized. Less than 10% of PH domains bind phosphoinositide phosphates (PIPs) with high affinity and specificity. PH domains are distinguished from other PIP-binding domains by their specific high-affinity binding to PIPs with two vicinal phosphate groups: PtdIns(3,4)P2, PtdIns(4,5)P2 or PtdIns(3,4,5)P3 which results in targeting some PH domain proteins to the plasma membrane. A few display strong specificity in lipid binding. Any specificity is usually determined by loop regions or insertions in the N-terminus of the domain, which are not conserved across all PH domains. PH domains are found in cellular signaling proteins such as serine/threonine kinase, tyrosine kinases, regulators of G-proteins, endocytotic GTPases, adaptors, as well as cytoskeletal associated molecules and in lipid associated enzymes.
Jiyao W et al.(2023). "The conserved domain database in 2023.",