CAREER: The protein-mineral bond

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EAR-0745808LOWER, Stephen K.Forces are invisible yet their presence can be felt anywhere. For large organisms, like humans, the force of gravity exerts a controlling influence on our lives. For smaller organisms, like bacteria, gravity is a trivial force. Rather, intermolecular forces control the world of microbes. This CAREER proposal will explore forces at a range of spatial scales, from binding forces at the peptide-mineral interface to the gravitational attraction that exists between humans and celestial objects. The research portion of this proposal will focus on measuring the energy landscapes of putative mineral-binding proteins and peptides. This will be accomplished by using atomic force microscopy (AFM) to examine the relationship between the transition force (i.e. rupture force) and the rate at which the force is applied to a particular protein-mineral pair. Proteins specimens will include putative mineral-binding proteins (MtrC and OmcA) from the metal reducing bacterium Shewanella oneidensis, as well as phage that express peptides with putative mineral-binding motifs, and artificial membranes doped with mineral-binding proteins. Mineral specimens will include crystalline, thin films of hematite (Fe2O3), goethite (FeOOH), pyrolusite (MnO2), and manganite (MnOOH). Molecular simulations will be used to determine the theoretical stability of putative mineral-binding motifs and the affinity of particular peptides towards specific mineral phases. This proposed work will (1) determine fundamental kinetic and thermodynamic properties such as, the free energy of dissociation, the rate of dissociation, and the distance to the transition barrier, for each peptide-mineral pair (e.g., MtrC-hematite); (2) define the mineral substrate(s) for each protein (MtrC and OmcA) based on fundamental binding elements; (3) define the boundaries of mineral-binding domains within the primary sequences of MtrC and OmcA; (4) determine whether putative mineral-binding domains within MtrC or OmcA are similar or dissimilar to mineral-binding motifs evolved by phage; (5) compare the measured kinetic/thermodynamic data to values predicted by molecular simulations of peptide-mineral bonds; (6) use the binding force-signature of MtrC and OmcA to create affinity maps that show the location of specific proteins on the surface of living cells. Broader impact One of the great strengths of Geological/Earth Science is the breadth of time and space that are encompassed by this discipline. This proposal describes an educational outreach program that teaches students from elementary to graduate school about forces that exist from the nanometer length-scale (e.g., intermolecular forces) to the infinite (e.g., the gravitational force). Students who participate in the proposed outreach programs will come away with a much stronger appreciation of the fundamental forces within our universe and their impact on living organisms. The educational outreach portion of this proposal will create a lecture series on "Forces in Natur" and a complementary lab related to subsurface transport of bacteria. This lecture and lab will be taught every year to about 1500 undergraduate students enrolled in a class called Planet Earth. Education majors enrolled in the Planet Earth class will, in turn, assist the PI as he conducts a one-week summer camp for elementary school students at one of the local, pubic schools. This camp will consist of hands-on experiments related to microbiology, polymers, and forces. On the final day of camp, the students will teach the "teachers", that is, the children will guide the parents/teachers through the same experiments the children performed earlier in the week. The education outreach plan also includes a proposed scientific "test of astrology" that will be run in the university newspaper, which is available to about 50,000 students. This test draws a novel comparison between the gravitational force and the idea that celestial objects exert a force of influence on our lives. Finally, this award will fund three students (two undergraduate and one graduate student) who will participate in the proposed research project described above.