Involved in cell-matrix and cell-cell adhesion interactions that are required for normal development. May participate in the linkage between muscle fiber and basement membrane. May play a role in endochondral ossification of bone and branching morphogenesis of lung. Binds heparin. At neuromuscular junctions, may play a role in acetylcholine receptor clustering (PubMed:26626625). Homotrimer; disulfide-linked. Nucleation of the type XIII collagen triple helix is likely to occur at the N-terminal region with triple helix formation proceeding from the N- to the C-terminus. Interacts with FN1, perlecan/HSPG2 and NID2. Additional isoforms seem to exist. Widely expressed in both fetal and adult ocular tissues (at protein level). In the eye, expression is accentuated in the ciliary muscle, optic nerve and the neural retina. In early placenta, localized to fibroblastoid stromal cells of the placental villi, to endothelial cells of developing capillaries and to cells of the cytotrophoblastic columns. Also detected in large decidual cells of the decidual membrane and to stromal cells of the gestational endometrium, but not in the epithelial cells in the endometrial glands. Isoform 10: Expressed in muscle (PubMed:26626625). The disease is caused by variants affecting the gene represented in this entry.