Discrete integration of collagen XVI into tissue-specific collagen fibrils or beaded microfibrils

The structural and functional diversity of extracellular matrices is determined, not only by individual macromolecules, but even more decisively, by the alloyed aggregates they form. Although quantitatively major matrix molecules can occur ubiquitously, their organization varies from one tissue to another due to their amalgamation with specific sets of minor components. Here, we show that the fibril-associated collagen with interrupted triple helices collagen XVI is unique in that, depending on the tissue context, it can be incorporated into distinct suprastructural aggregates. In papillary dermis, the protein unexpectedly does not occur in banded collagen fibrils, but rather, is a component of specialized fibrillin-1-containing microfibrils. In territorial cartilage matrix, however, collagen XVI is not a component of aggregates containing fibrillin-1. Instead, the protein resides in a discrete population of thin, weakly banded collagen fibrils also containing collagens II and XI. Collagen IX also occurs in this population of fibrils, but at longitudinal locations discrete from those of collagen XVI. This suprastructural versatility of a collagen is without precedent and highlights pivotal differences in the tissue-specific organization of matrix aggregate structures.