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 (PubMed:27119146). 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 (PubMed:23959653, PubMed:27119146, PubMed:28115524). Interacts with PLOD1, P3H3 and PPIB. Identified in a complex with PLOD1 and P3H3. Detected in calvaria, cartilage, kidney, ribs, and at lower levels in tail (PubMed:23959653, PubMed:27119146). Detected in proliferating and prehypertrophic chondrocytes in the growth plate of long bones and in mineralizing chondro-osseus bone collar and cortical bone (PubMed:23959653). Detected on osteoblasts in long bones (PubMed:23959653, PubMed:27119146). Detected in skin fibroblasts (at protein level) (PubMed:27119146). Detected in fetal ribs, and in tibia and metatarsus from neonates (PubMed:23959653). No visible phenotype at birth (PubMed:23959653, PubMed:27119146, PubMed:28115524). Mice are born at the expected Mendelian rate (PubMed:23959653, PubMed:27119146). Two and six month old mutant mice display a decreased ratio between trabecular bone volume and tissue volume in tibia and femur, plus decreased connectivity density in femur and tibia (PubMed:23959653, PubMed:27119146). Osteoblast number is not affected, while osteoclast numbers are increased, suggesting that increased bone resorption is the cause for the low bone mass phenotype (PubMed:23959653). Lysine hydroxylation of skin and bone collagen alpha chains is strongly reduced (PubMed:27119146, PubMed:28115524). In contrast, prolyl 3-hydroxylation is not affected (PubMed:23959653, PubMed:27119146). Dorsal skin displays impaired packing of collagen fibrils, decreased skin tensile strength, decreased skin stiffness and increased skin fragility (PubMed:27119146, PubMed:28115524). Likewise, mice deficient for both P3h3 and P3h4 display decreased lysine hydroxylation of collagen alpha chains, but normal collagen prolyl 3-hydroxylation (PubMed:28115524). Belongs to the leprecan family.