Simon Fraser University (SFU) research is yielding new insights into one of the most perplexing properties of collagen. A recent paper by physics professor Nancy Forde and postdoctoral researcher Alaa Al-Shaer describes key molecular features that helps enable this notoriously unstable protein to maintain its structure.
Collagen makes up approximately 20 per cent of the protein found in our bodies. It provides stability to our connective tissues such as tendon, bone, cartilage and skin, and forms a scaffold in which cells grow and thrive.
It is also a protein that has puzzled scientists for a long time. How can a molecule that is structurally unstable at body temperature play such an important role in helping to hold our bodies together? Understanding this may be key to learning how we can better treat collagen-associated diseases such as brittle bone disease, Ehlers-Danlos Syndrome and diabetes.
Alaa Al-Shaer used atomic force microscopy to record images of collagen IV
Individual collagens are too small to be seen using conventional light microscopes so Al-Shaer used a technique called atomic force microscopy (AFM) to capture images of collagen proteins at different temperatures. Forde explains that this technique allows researchers to "feel" objects much like reading Braille or a needle on a record.
When stable, collagen has a triple-helix structure with three strands twisted together like rope or yarn. At higher temperatures these threads unravel into random coils. Al-Shaer recorded hundreds of images to map this process of unravelling, and how in some cases the proteins were able to fold back together when cooled.
She found that amino acids present in collagen IV called cysteines can form bonds between individual strands that can "staple" them together. Where these staples exist, collagen IV resisted unravelling when heated and was more likely to repair itself as it cooled. Collagens without these bonds fell apart more easily and were not able to reassemble when cooled.
When she searched protein sequence databases for similar cysteines in other species, Al-Shaer found that this chemical staple is very common in collagen IV from other multicellular life forms, including some species that first evolved very long ago. "This indicates these cysteines have an important functional role," Forde explains, "since if they had mutated to something else and done just as good a job, we'd expect to see other amino acids at these positions."
"This study was the first time we have used AFM imaging to study the stability of collagen at different temperatures and map the folding and unfolding pathways. We think this is incredibly promising for answering future questions for the field," says Forde.
Forde notes that many previous studies on collagen stability have used short strands of synthetic peptides. "It is hard to know how well lessons learned in these small peptide studies translate into effects within the full-length collagen proteins, whose sequences are far more complex," she says. AFM can help verify or challenge those results.
Forde notes that multiple graduate and undergraduate students have helped to advance her lab's work on collagen, and her team is looking forward to further developing these techniques to answer many other questions.
"We would like to look at mutated or otherwise chemically altered collagens that are associated with disease and aging, in order to understand the mechanism of disease better," she says. "And I want to continue working with amazing students in SFU's Faculty of Science to make these discoveries!"
