Part of a complex composed of PLOD1, P3H3 and P3H4 that catalyzes hydroxylation of lysine residues in collagen alpha chains and is required for normal assembly and cross-linking of collagen fibrils. Required for normal bone density and normal skin stability via its role in hydroxylation of lysine residues in collagen alpha chains and in collagen fibril assembly. Interacts with PLOD1, P3H3 and PPIB. Identified in a complex with PLOD1 and P3H3. Found in testis, brain, heart and at a much lower level in liver. Belongs to the leprecan family. Was initially identified in the synaptonemal complex (PubMed:1363622). Characterization data from human and mouse indicate the protein is in the endoplasmic reticulum, which agrees with its biological function and the predicted signal sequence. Truncated N-terminus.