The pro-α3(V) collagen chain -: Complete primary structure, expression domains in adult and developing tissues, and comparison to the structures and expression domains of the other types V and XI procollagen chains

The low abundance fibrillar collagen type V is widely distributed in tissues as an alpha 1(V)(2)alpha 2(V) heterotrimer that helps regulate the diameters of fibrils of the abundant collagen type I. Mutations in the alpha 1(V) and alpha 2(V) chain genes have been identified in some cases of classical Ehlers-Danlos syndrome (EDS), in which aberrant collagen fibrils are associated with connective tissue fragility, particularly in skin and joints, Type V collagen also exists as an alpha 1(V)alpha 2(V)alpha 3(V) heterotrimer that has remained poorly characterized chiefly due to inability to obtain the complete primary structure or nucleic acid probes for the alpha 3(V) chain or its biosynthetic precursor, pro-alpha 3(V), Here we provide human and mouse full-length pro-alpha 3(V) sequences. Pro-alpha 3(V) is shown to be closely related to the alpha 1(V) precursor, pro-alpha 1(V), but with marked differences in N-propeptide sequences, and collagenous domain features that provide insights into the low melting temperature of alpha 1(V)alpha 2(V)alpha 3(V) heterotrimers, lack of heparin binding by alpha 3(V) chains and the possibility that alpha 1(V)alpha 2(V)alpha 3(V) heterotrimers are incorporated into heterotypic fibrils, In situ hybridization of mouse embryos detects alpha 3(V) expression primarily in the epimysial sheaths of developing muscles and within nascent ligaments adjacent to forming bones and in joints. This distribution, and the association of alpha 1(V), alpha 2(V), and alpha 3(V) chains in heterotrimers, suggests the human alpha 3(V) gene COL5A3 as a candidate locus for at least some cases of classical EDS in which the alpha 1(V) and alpha 2(V) genes have been excluded, and for at least some cases of the hypermobility type of EDS, a condition marked by gross joint laxity and chronic musculoskeletal pain. COL5A3 is mapped to 19p13.2 near a polymorphic marker that should be useful in analyzing linkage with EDS and other disease phenotypes.