May catalyze the post-translational formation of 4-hydroxyproline in -Xaa-Pro-Gly- sequences in the 6 collagen-like proteins of Mimivirus. 2-oxoglutarate + L-prolyl-[collagen] + O2 = CO2 + succinate + trans-4-hydroxy-L-prolyl-[collagen] Belongs to the P4HA family.