The basement membrane zones of the dermal-epidermal junction of skin and of several other external tissues are more complex than the basement membranes of more internal tissues. This specialized complexity is reflected both ultrastructurally by the presence of unique fibrous structures, and immunologically by the presence of antigens not found in other basement membranes. The anchoring fibril is one of these structures. The anchoring fibril is a centrosymmetrically banded fiber, about 800 nm in length, whose major structural component is Type VII collagen. The anchoring fibril subunit is an antiparallel linear dimer of Type VII collagen molecules crosslinked to each other at their amino terminii through an overlap of 60 nm. The distal ends of the anchoring fibril contains large carboxy-terminal globular domains of this collagen type. Each Type VII molecule contributes a domain of approximately 450 kd. Often these globular domains at one end of the anchoring fibril are embedded within the lamina densa. Anchoring fibril can either form a horseshoe-shaped structure with the distal end also inserting into the lamina densa, or it can extend perpendicular to the basal lamina into the dermis with its distal end inserted into what appears as an amorphous patch. This amorphous """"""""island"""""""" contains aggregates of carboxy-terminal globular domain of Type VII collagen, Type IV collagen, laminin and perhaps other basement membrane components. Additional anchoring fibrils can bridge these islands, and are seen projecting further into the dermis, again terminating in additional islands. As a result, the anchoring fibrils form an extended network 1-1/2 to 2 Mu into the dermis. We propose to examine the intermolecular interactions responsible for the formation and stabilization of this network, by identifying and quantitating these interactions at the molecular level. This will be done by isolating reactive fragments from the interacting components, determining the amino acid sequence of the interactive regions, and relating these to the amino acid sequence fo the carboxy-terminal globular domain of Type VII collagen. An analysis of this extended network of anchoring fibrils within the subbasal lamina of patients with recessive-dystrophic Epidermolysis Bullosa will help to determine the function of this network as well as contribute to our understanding of the molecular pathology of this disease condition.
