COL23A1 is a member of the transmembrane collagens, a subfamily of the nonfibrillar collagens that contain a single pass hydrophobic transmembrane domain.The N-terminal cytoplasmic and transmembrane domains are required for cell surface targeting. Banyard et al. (2003) demonstrated that rat COL23A1 is expressed as a 75-kD species on the cell surface and is cleaved by furin protease to release a soluble 60-kD product that can form homotrimers. Using truncation mutants, Banyard et al. (2003) demonstrated that the predicted furin-cleaved secreted portion of human COL23A1 also formed multimers and displayed low affinity binding to heparin in vitro. By genomic sequence analysis, Banyard et al. (2003) mapped the COL23A1 gene to chromosome 5q35 and the mouse homolog to chromosome 11B1+2.