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Avo1 Pleckstrin homology (PH) domain Target of rapamycin (TOR) is a highly conserved serine/threonine protein kinase and a central controller of the growth, metabolism and ageing of eukaryotic cells. TOR assembles into two protein complexes termed TOR complex 1 (TORC1) and TOR complex 2 (TORC2) which function as central nodes in a complex network of signal transduction pathways that are involved in normal physiological as well as pathogenic events. TORC1 mediates the rapamycin-sensitive signalling branch, which positively regulates anabolic processes and negatively regulates catabolic processes. TORC2 signalling is rapamycinin insensitive and is involved in the spatial aspects of cell growth by controlling the actin cytoskeleton and cell polarity. In Saccharomyces cerevisiae, TORC2 is involved in the regulation of ceramide metabolism. In S. cerevisiae, TORC1 consists of the proteins Kog1, Lst8, Tco89 and either Tor1 or Tor2, while TORC2 consists of the proteins Avo1, Avo2, Avo3, Bit61, Lst8 and Tor2. The C-terminal domain of the Saccharomyces cerevisiae TORC2 component Avo1 is required for plasma-membrane localization of TORC2 and is essential for yeast viability. The C-termini of Avo1 and Sin1, its Human ortholog, both have the pleckstrin homology (PH) domain fold. Comparison with known PH-domain structures suggests a putative binding site for phosphoinositides. 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.",