Collagen is the most abundant protein of the human body. It provides structural integrity in the human body and is responsible for multiple interactions with cells and other matrix molecules. Many common diseases, such as arthritis, diabetes, and cancer involve abnormal regulation or reactivity of collagen, and certain genetic diseases that arise from collagen mutations result in connective tissue disease or aortic aneurism. Although the collagen triple helix has a relatively uniform rod-like structure, with an amino acid sequence of (Gly-X-Y)n repeats, subtle alterations in structure and dynamics along the collagen chain are critical to many biological events. It is outstanding how proteins can recognize specific sites in collagen and how a simple Gly mutation on collagen sequence can lead to severe diseases. Our laboratory uses an integrated approach based on high-field NMR in conjunction with computational, biophysical, and biological methods to provide unique structural and dynamic insight at the atomic-level into protein recognition of collagen and to understand the molecular basis of collagen diseases arising from mutations.
Collagen mutations associated with disease:
The substitution of a single Gly by another amino acid breaks the characteristic repeating (Gly-X-Y)n sequence pattern of collagen and results in connective tissue disease. Gly mutations in collagen type I in bone, tendons, and skin result in Osteogenesis Imperfecta (OI), which is characterized by brittle bones with phenotypes ranging from non-lethal to lethal. Mutations to collagen type III in blood vessels and hollow organs result in vascular Ehlers-Danlos Syndrome (vEDS), the most detrimental of EDS genetic connective tissue diseases, and lead to arterial, intenstinal, and uterine rupture. We ask: How do detrimental G-->X mutations impact collagen triple helix structure, dynamics, stability, and protein binding in order to establish a sequence-structure/dynamics-biological function relationship relevant to disease.
Collagen-protein interactions regulate biological function:
Collagen is highly biologically active, interacting with cellular receptors, such as integrins, matrix metalloproteinases (MMPs) during degradation, and other extra cellular matrix (ECM) components. These collagen interactions are critical for biological function, however in other cases, improper interactions with collagen may be detrimental. Our lab studies collagen binding to integrin receptors, α1β1 and α2β1, through their α1 and α2 I-domains. Specific binding of integrins to collagen plays a critical role in numerous cellular adhesion processes including platelet activation and aggregation, a key process in clot formation, and cancer metastasis. In our research, we ask: How does the integrin I-domain select, recognize and bind collagen? The interaction of collagen with β2-microglobulin (β2m) is pathological and results in β2m amyloid fibrils in the joints of long-term hemodialysis patients, termed dialysis-related amyloidosis (DRA). We ask: How is β2m structurally and dynamically perturbed by its interaction with collagen to promote amyloid formation?
Understanding the complex architecture of the collagen fibril for access to cryptic binding sites:
Triple helical monomers of fibrillar collagens pack into a complex, supramolecular fibril architecture. Although in the long, rod-like triple helix, all interaction sites are exposed and available for binding, the packing of the fibril obstructs many of these interactions sites, hiding them from the exposed fibril surface. Since critical biological processes requiring access to binding sites still occur, such as cellular attachment and MMP cleavage, we ask: How does the complex collagen architecture regulate protein binding? To answer this question, we probe the internal dynamics of the collagen type I fibril by MD simulations and use microscopy to visualize collagen fibrils and monomers and their binding partners.