Type XIII is a non-fibril-forming type II transmembrane protein with a large amino terminal NC1 domain. This domain has a hydrophobic membrane-spanning segment that anchors the molecule to the plasma membrane and a large extracellular, mostly collagenous carboxyterminal domain (Hägg et al. 1998). Recombinant type XIII collagen can form homotrimers with triple-helical collagenous domains (Snellman et al. 2000a). It is detected at low levels in all connective tissue-producing cells; in cultured cells it is localized in focal adhesions (Hägg et al. 2001). The extracellular region has an adhesion-related function (Hägg et al. 2001) that is involved in formation of the neuromuscular junction (Latvanlehto et al. 2010). The purified protein has been shown to interact with Integrin alpha1beta1 (Nykvist et al. 2000). An N-terminal ectodomain portion of type XIII collagen is cleaved in culture medium by a furin-like protease (Snellman et al. 2000b, Väisänen et al. 2004). This ectodomain interacts with fibronectin, nidogen-2 and perlecan (Tu et al. 2002, Väisänen et al. 2006).