Collagen XVII is a transmembrane component of hemidesmosomal cells with important functions in epithelial-basement membrane interactions. Here we report on properties of the extracellular ectodomain of collagen XVII, which harbors multiple collagenous stretches. We have recombinantly produced subdomains of the collagen XVII ectodomain in a mammalian expression system. rColXVII-A spans the entire ectodomain from ␦NC16a to NC1, rColXVII-B is similar but lacks the NC1 domain, a small N-terminal polypeptide rColXVII-C encompasses domains ␦NC16a to C15, and a small C-terminal polypeptide rColXVII-D comprises domains NC6 to NC1. Amino acid analysis of rColXVII-A and -C demonstrated prolyl and lysyl hydroxylation with ratios for hydroxyproline/proline of 0.4 and for hydroxylysine/lysine of 0.5. A small proportion of the hydroxylysyl residues in rColXVII-C (ϳ3.3%) was glycosylated. Limited pepsin and trypsin degradation assays and analyses of circular dichroism spectra clearly demonstrated a triple-helical conformation for rColXVII-A, -B, and -C, whereas the C-terminal rColXVII-D did not adopt a triple-helical fold. These results were further substantiated by electron microscope analyses, which revealed extended molecules for rColXVII-A and -C, whereas rColXVII-D appeared globular. Thermal denaturation experiments revealed melting temperatures of 41°C (rColXVII-A), 39°C (rColXVII-B), and 35°C (rColX-VII-C). In summary, our data suggest that triple helix formation in the ectodomain of ColXVII occurs with an N-to C-terminal directionality.Collagen XVII, also known as the 180-kDa bullous pemphigoid antigen (BP180), is a transmembrane protein that is widely known as a structural component of hemidesmosomes, although structures at cell-tissue interfaces other than hemidesmosomes may also contain collagen XVII (1, 2). Mutations in the collagen XVII gene, COL17A1, lead to junctional epidermolysis bullosa, a hereditary blistering skin disease with epidermal detachment from the basement membrane (3).The cDNA sequence of collagen XVII encodes a type II integral transmembrane protein of 1497 amino acid residues (4). It consists of an intracellular domain of 466 residues, a transmembrane domain of 23 residues, and an extracellular collagenous domain of 1008 amino acids with multiple non-collagenous interruptions. The length of the individual collagenous regions varies from 14 to 242 amino acid residues (4). Collagen XVII exists in two molecular forms, i.e. as a full-length transmembrane homotrimer of three 180-kDa ␣1(XVII) chains and as a 120-kDa soluble form. The latter corresponds to the extracellular domain and is presumably released from the cell surface by furin-mediated proteolytic processing (5). In some instances, an even shorter fragment with ϳ90 -100 kDa has been observed (6).Some information about the molecular shape of collagen XVII under physiological conditions can be deduced from rotary shadowing electron microscopy of collagen XVII from bovine cell lines or from recombinant fragments. These studies revealed asymmetr...

The aim of this study was to investigate the extent of lysyl and prolyl hydroxylation of collagen I in osteoporosis and compare it with collagen I from "bone healthy" individuals. Collagen I was isolated from femoral heads of osteoporotic women, from women suffering from osteoarthrosis of the hip, and from healthy women 60-85 years of age. The femoral heads were dissected into compact and trabecular bone of the neck region and from trabecular bone of the head region, and collagen I was extracted by limited pepsin digestion. The amino acid analysis of individual alpha-chains showed a remarkably higher degree of hydroxylation of lysine residues both in the alpha1(I)- and in the alpha2(I)-chains in osteoporotic bone compared with osteoarthrotic and "normal" bone, whereas the prolyl hydroxylation was nearly unchanged. The lysyl overhydroxylation was observed in the compact as well as in the trabecular bone of osteoporotic femoral heads. These biochemical alterations may play a crucial role in the pathogenesis of osteoporosis.