Collagen in the lab
doi:10.1038/nindia.2008.206 Published online 21 May 2008
When Gopalasamudram Narayana Iyer Ramachandran reported the triple helical structure of collagen in 1955, it was hailed as one of the seminal works in the understanding of the peptide structure. His work resulted in the 'Ramachandran plot’ that became a standard description of protein structures in text books.
More than half a century later, an Indian-American has achieved in a synthetic system what Ramachandran observed in collagen inside the human body. Shyam Rele, along with colleagues from the Emory University School of Medicine in Atlanta, USA, has generated for the first time a synthetic collagen analog, which self assembles into microfibers in the laboratory. This means that human collagen-like fibrils can be 'manufactured' in the lab — a pathbreaking feat in the field of nanotechnology and bio-inspired biomaterials.
For the last three decades, scientists have been trying to synthesize and emulate remarkable properties of collagen — the connective tissue that holds together our skin, bones, cartilage and teeth — but have not been able to mimic the long, fibrous molecules found in nature. Rele and his colleagues Elliot Chaikof and Vince Conticello from the Laboratory of Bio-Molecular Engineering and Advanced Vascular Technologies at Emory, have designed and synthesized the first ever Synthetic Collagen Peptide system which is 36 amino acid unit long and self-assembles into a fibrous structure with well-defined periodicity reminiscent of native collagen observed in the human body.
Rele, a Ph. D in synthetic organic chemistry and natural product chemistry from the Bhaba Atomic Research Centre in Mumbai, is thrilled at the opportunities his team's findings could open up in the treatment of cardiovascular, orthopaedic, and neurological diseases as well as in protein folding catalyst design, bio-nanotechnology, tissue engineering and origins of life research. “We have mimicked Nature on a nanoscale,” he says.
After majoring in chemistry from Wilson College, Mumbai, Rele taught in the same college and then at K.C. College, Mumbai. Currently he works as a senior scientist in a Pasadena-based RNAi therapeutic biophramaceutical company. He draws inspiration from Ramachandran's path-breaking discovery. "The solid foundation laid by him has provided the starting point for the present research involving generation of self-assembled synthetic collagen nanofibers. On a personal level, it shows me how research could be influenced and accomplished through ingenuity and imagination using simple techniques available at that period of time," Rele says.
Collagen, he says, is one of the important components of the extracellular matrix comprising the major structural protein component of higher organisms. It has been a major challenge for scientists to emulate the unique structural and biological properties of native collagenous biomaterials in synthetic analogues.
"Consequently, numerous opportunities exist for synthetic collagens in biomedical applications as extra-cellular matrix analogues, if the appropriate materials can be constructed that retain and expand upon the desirable properties of native collagen fibrils," he explains.
The Emory team's synthesized peptide protomer, which is made up of three heterotrimeric peptide repeat units, contains a hydrophobic proline-hydroxyproline-glycine core flanked on both the sides by distinct sets of peptide repeats. These repeats contain either negatively (glutamic acid) or positively (arginine) charged amino acid residues. When positioned appropriately, these charged amino acids bias and adopt the triple helical self-assembly which generate fibrils at physiological temperatures producing D-periodic microfibers. The smooth fibrils generated were hundreds of nanometers long and tens of nanometers in diameter. These fibrils displayed tapered tips similar to the tactoidal ends of native collagen fibers. "Fiber growth would continue from these ends," Rele observes.
Generation of such nanostructured molecules which mimic native structural proteins will lay the future ground work for unraveling complex phenomena including collagen fiber formation in protein conformational diseases and for the design of new materials with biological, chemical, and mechanical properties that exceed those of currently available synthetic polymers.
The propensity of generating such self-assembling, biologically compatible peptide scaffolds to arrange themselves into fibers, tubules, and a variety of geometrical layers, establishes an important substrates for cell growth, differentiation, and biological function.
"By precisely recreating the structure of proteins found in nature, perhaps we can mimic their function or get a better handle to create new biologically inspired systems that achieve the same results," Rele says.
The team's long term goal is to manipulate and create more complex biomaterials such as artificial organs and engineered living tissues along with cell-based therapies, all of which will define the evolving field of regenerative medicine.
- Ramachandran, G. N. et al. Structure of Collagen. Nature 176, 593-595 (1955)
- Rele, S. et al. D-Periodic Collagen-Mimetic Microfibers. J. Am. Chem. Soc. 129, 14780-14787 (2007)