This is the N-terminal domain of TTC7, a protein that forms the regulatory subunit of the PI4KIIIalpha complex (also known as PI4KA). This complex is composed of PI4KIIIalpha, TTC7 and FAM126A and catalyses the first step in plasma membrane phosphoinositide synthesis. This TTC7 N-terminal domain contains basic residues suitable for interaction with the acidic inner leaflet of the plasma membrane and is required for localising the active site near its substrate. TTC7 acts as a bridge between PI4KA and EFR3B-FAM126A, via direct interactions. ERF3B is not part of the complex but contributes to its recruitment to the membrane [1,2].

1: The leukodystrophy protein FAM126A (hyccin) regulates PtdIns(4)P synthesis at the plasma membrane. Baskin JM, Wu X, Christiano R, Oh MS, Schauder CM, Gazzerro E, Messa M, Baldassari S, Assereto S, Biancheri R, Zara F, Minetti C, Raimondi A, Simons M, Walther TC, Reinisch KM, De Camilli P; Nat Cell Biol. 2016;18:132-138. PMID:26571211

2: Architecture of the human PI4KIIIalpha lipid kinase complex. Lees JA, Zhang Y, Oh MS, Schauder CM, Yu X, Baskin JM, Dobbs K, Notarangelo LD, De Camilli P, Walz T, Reinisch KM; Proc Natl Acad Sci U S A. 2017;114:13720-13725. PMID:29229838