BMAT: Self-assembly of extensin glycoproteins for designing novel plant-based biopolymers

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Non-technical summaryAll living creatures on earth are made of cells. Each cell is enclosed by an extracellularmatrix. You can think of an extracellular matrix as a housing that protects and containsa cell’s contents. In plants, that housing is particularly strong and rigid and is composedof a wide variety of biopolymers. One such polymer is known as extensin. As its nameimplies, extensin plays an important role in controlling plant growth and extension, andit does so by forming a polymeric molecular scaffold or frame. This work aims tounderstand what governs scaffold formation at the molecular level and how we can usethis knowledge to design new biopolymers that mimic or imitate the properties ofnatural extensins. In the face of global climate change, our reliance on fossil fuels mustbe reduced, not only for use as transportation fuels, but also as chemical/polymerfeedstocks. Potential industrial applications of this research are numerous and includethe creation of biodegradable plastics, molecular electronics, food enhancement,cosmetics additives, etc. This research will also provide training opportunities forundergraduate and graduate students in biophysical chemistry and biochemistry. Newundergraduate course materials for physical chemistry and biochemistry will bedeveloped, and various outreach and scientific literacy projects for primary/secondaryschool aged children and adults are planned.Technical summaryExtensins (EXTs) are network-forming hydroxyproline-rich glycoproteins foundnaturally in plant cell walls. Monomeric EXTs self-assemble to form insoluble polymericcell wall scaffolds. Very little is known about what governs EXT self-assembly at themolecular level. Atomic force microscopy (AFM) has been previously used to explorethe behavior of EXT self-assembly. These studies showed that EXT monomersspontaneously self-assemble into intricate dendritic scaffolds. Furthermore, differentEXT types displayed different self-assembly behaviors, whereby some EXTs favoredmore xy-plane growth (termed ‘branching’), while others displayed z-plane growth(termed ‘stacking’). These changes were attributed to differences in the repetitive,modular, and amphiphilic nature exhibited by different EXTs. To better understand themolecular drivers of EXT self-assembly, three objectives are proposed. First, will befurther characterize the self-assembly of native EXT glycoproteins by AFM to studytheir kinetics, pore sizes, and relative growth in the x-, y-, and z-planes. Syntheticbiology will then be used to create biomimetic EXTs that vary in amphiphilicity,modularity, and repetitiveness and test for their self-assembly behavior using AFM.Lastly, the biochemical and biophysical properties of synthetic self-assembled EXTs willbe characterized and compared with a focus on monomer adhesion strength andpolymer flexibility. Elucidating the molecular rules that govern EXT self-assembly isexpected to facilitate the rational design of synthetic, plant-based biomimeticbiopolymers.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.