Orientation of type VI collagen monomers in molecular aggregates.

Type VI collagen, prepared from guanidine extracts of human amnion, contains very little monomeric material, the major forms being dimers and tetramers. In order to study the orientation of the molecules in these aggregates, they were digested with pepsin followed by bacterial collagenase. Two fragments were isolated, one containing part of the inner globular domain still attached to part of the triple helix and the other containing large fragments of the outer globular domain. Each fraction was further analyzed; peptides were isolated and their amino-terminal amino acid sequences determined. By comparing the determined sequences with published data, it was found that the outer globular domain contained sequences derived from the amino-terminal domain of all three chains of type VI collagen whereas the inner globular domain contained sequences from the carboxy-terminal domain. This provided direct chemical evidence that dimers and tetramers of type VI collagen are formed by overlapping carboxy-terminal regions of the monomers.