Substrate receptor subunit of a cullin-RING superfamily E3 ligase complex (CUL5-based E3 ubiquitin ligase complex) which mediates the ubiquitination and subsequent proteasomal degradation of target proteins. Depending of the metabolic state of the cell, promotes the proteasomal degradation of IMPDH2, the rate-limiting enzyme in GTP biosynthesis or protects IMPDH2 by stabilizing IMPDH2 filaments assembly. Implicated in different cellular processes, like copper homeostasis and cell proliferation. Protein modification; protein ubiquitination. Part of an E3 ubiquitin-protein ligase complex with Elongin BC (ELOB and ELOC), CUL5 and ANKRD9. Interacts with IMPDH2; leading to ubiquitination of IMPDH2 and its subsequent proteasomal degradation. Detected in long filamentous cytosolic structures where it colocalizes with IMPDH2. Under basal conditions ANKRD9 is mainly in vesicle-like structures, upon nutrient limitation (guanine nucleotides deficiency) ANKRD9 loses its vesicular pattern and assembles with IMPDH2 into rodlike filaments.