Probable muscle-intrinsic activator of MUSK that plays an essential role in neuromuscular synaptogenesis. Acts in aneural activation of MUSK and subsequent acetylcholine receptor (AchR) clustering in myotubes (By similarity). Accumulates at neuromuscular junctions. The PH domain mediated binding to phospholipids with phosphoinositol headgroups. Affinity is highest for phosphatidyl 3,4,5-trisphosphate, followed by phosphatidylinositol 3,4-bisphosphate and phosphatidylinositol 4,5-bisphosphate (By similarity).