TYPE-XV COLLAGEN EXHIBITS A WIDESPREAD DISTRIBUTION IN HUMAN TISSUES BUT A DISTINCT LOCALIZATION IN BASEMENT-MEMBRANE ZONES

The collagen family of proteins consists of 19 types encoded by 33 gen es. One of the more recently discovered collagens is the alpha 1 chain of type XV. Type XV collagen is comprised of a 577-amino-acid, highly interrupted, triple-helical region that is flanked by amino and carbo xy noncollagenous domains of 555 and 256 residues, respectively. To ad dress questions of where this collagen is localized and what its funct ion may entail, we produced a bacteria-expressed recombinant protein r epresenting the first half of the type XV collagen carboxy-terminal do main in order to generate highly specific polyclonal antisera. Immunos creening: of an expression library with the affinity-purified antibody revealed three clones coding for part of the type XV triple-helical r egion and the entire noncollagenous carboxy-terminus. Western blot ana lysis of human tissue homogenates identified a 116-kDa collagenase-sen sitive protein and a 27-kDa collagenase-resistant fragment, whose elec trophoretic mobilities were unchanged in the presence and absence of r eductant. Northern blot hybridization to human tissue RNAs indicated t hat type XV has a prevalent and widespread distribution. To determine the precise localization of type XV collagen, immunohistochemical anal yses at the light- and electron-microscopic levels were performed. Typ e XV exhibited a surprisingly restricted and uniform presence in many human tissues as evidenced by a strong association with vascular, neur onal, mesenchymal, and some epithelial basement membrane zones. These data suggest that type XV collagen may function in some manner to adhe re basement membrane to the underlying connective tissue stroma.