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 (PubMed:30293565). 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 (PubMed:30293565, PubMed:31337707). Implicated in different cellular processes, like copper homeostasis and cell proliferation (PubMed:24522796, PubMed:30293565). Protein modification; protein ubiquitination. Part of an E3 ubiquitin-protein ligase complex with Elongin BC (ELOB and ELOC), CUL5 and ANKRD9 (PubMed:30293565). Interacts with IMPDH2; leading to ubiquitination of IMPDH2 and its subsequent proteasomal degradation (PubMed:31337707). Detected in long filamentous cytosolic structures where it colocalizes with IMPDH2 (PubMed:31337707). 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 (PubMed:31337707).