FYVE, RhoGEF and PH domain containing/faciogenital dysplasia proteins 1-4 and similar proteins, N-terminal Pleckstrin homology (PH) domain
In general, FGDs have a RhoGEF (DH) domain, followed by an N-terminal PH domain, a FYVE domain and a C-terminal PH domain. All FGDs are guanine nucleotide exchange factors that activates the Rho GTPase Cdc42, an important regulator of membrane trafficking. The RhoGEF domain is responsible for GEF catalytic activity, while the N-terminal PH domain is involved in intracellular targeting of the DH domain. Mutations in the FGD1 gene are responsible for the X-linked disorder known as faciogenital dysplasia (FGDY). Both FGD1 and FGD3 are targeted by the ubiquitin ligase SCF(FWD1/beta-TrCP) upon phosphorylation of two serine residues in its DSGIDS motif and subsequently degraded by the proteasome. They play different roles to regulate cellular functions, even though their intracellular levels are tightly controlled by the same destruction pathway. FGD4 is one of the genes associated with Charcot-Marie-Tooth neuropathy type 4 (CMT4), a group of progressive motor and sensory axonal and demyelinating neuropathies that are distinguished from other forms of CMT by autosomal recessive inheritance. Those affected have distal muscle weakness and atrophy associated with sensory loss and, frequently, pes cavus foot deformity. 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.",