Self-Assembly of Collagen Triple Helices into Higher Order Structures

About This Grant

With the support of the Macromolecular, Supramolecular, and Nanochemistry Program in the Division of Chemistry, Dr. Jeffrey D. Hartgerink of Rice University aims to reveal the atomic structure of collagen, the most abundant protein in the human body. Collagen is a remarkable protein which undergoes multiple levels of assembly. The beautiful final product controls an incredibly wide range of biological behavior including tissue integrity, cancer metastasis, wound healing, effective response to viral and bacterial invaders, and even weight regulation. Amazingly, despite early studies dating back to the 1950’s, collagen is very poorly understood. Without an accurate structure, advances in all these areas will be limited. The research team has recently discovered that bundled collagen can take on a never-before-observed shape. The team will explore the circumstances under which this novel shape is formed, undertaking studies with potential to reveal the mysteries of collagen superstructure that have evaded sight for over seventy years. This work expects to lay out chemical methods allowing scientists to mimic biological materials, which may lead to breakthroughs in tissue regeneration, immunology, and cancer research. This program will also serve as the basis to train the next generation of scientists including graduate students pursuing a PhD, undergraduates pursuing Chemistry and Bioscience degrees, and enhancing the pipeline of STEM focused students by engaging high school students and their teachers from Houston area schools. Recent discoveries by the Hartgerink lab related to collagen structure suggest that the fundamental structural unit – the collagen triple helix – can adopt a much wider range of superhelical twists than previously appreciated. This research will study the extent to which the superhelical pitch can be altered, its impact on the self-assembly of high molecular weight complexes, and the sequential circumstances in which this surprising flexibility is observed. The hypothesis is that superhelical unwinding is more likely to occur under the following conditions: 1) when helix-helix packing forces are significant, 2) at or near discontinuities in the required (Xaa-Yaa-Gly)n primary sequence of collagens, 3) at or near the N- and C- termini of a protein, 4) in regions with a low fraction of proline in the Xaa position, or in circumstances that combine two or more of the above. To test these hypotheses, the sequences of natural collagen in which one or more of the criteria above are present will be examined, and, using sequence-structure rules elucidated in this way, the de novo design of these unusual collagen assemblies will be performed. This project will make use of extensive solid-phase peptide synthesis, which allows for the high frequency incorporation of hydroxyproline, which is not genetically encoded. These peptides will be assessed for their ability to self-assemble into all varieties of triple helices using circular dichroism polarimetry and their ability to form higher-order assemblies first by size exclusion chromatography and, subsequently, by methods which allow for atomic precision including nuclear magnetic resonance spectroscopy, X-ray crystallography, and cryo-electron microscopy. The fundamental chemistry knowledge gained from this research is expected to expand the current understanding of collagen assembly, which could have transformative effects in a range of biomedical applications and materials science. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.