Forms hydroxylysine residues in collagen type IV (By similarity). Required for the secretion of collagen type IV (vkg) from haemocytes, fat body and follicle cells (PubMed:23369713, PubMed:20888931). 2-oxoglutarate + L-lysyl-[collagen] + O2 = (5R)-5-hydroxy-L-lysyl-[collagen] + CO2 + succinate Binds 1 Fe(2+) ion per subunit. Detected in the ER of fat body cells and haemocytes. Also detected in small puncta in the extracellular space, particularly in the region surrounding the haemocytes. Expressed throughout embryogenesis (at protein level). First detected at stage 12 in the haemocytes and in the fat body at stage 13 (at protein level). High levels also detected in the anal pads of stage 16 embryos (at protein level). RNAi-mediated knockdown in follicle cells results in round eggs. Collagen type IV protein vkg accumulates in the basal cytoplasm of the follicle cells and is likely to cause the distended ER region in the basal cytoplasm.