Biomolecule interactions on calcium carbonate and stoichiometrically similar biomedical, optical and electronic materials
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A combinatorial approach has been successfully used to characterize peptides that bind to four different surfaces of CaCO3 and six different oxide substrates that are chemically and stoichiometrically similar to CaCO3. A standard screening and a single substrate screening method were employed. Both methods used a bacteriophage combinatorial library with a complexity of 109 different random sequences. While geological (104) calcite screenings do not seem to show strong consensus, peptides screened against geological aragonite exhibit extraordinary consensus. Overall, peptides screened against aragonite were highly basic. Peptides screened against (110) geological aragonite show [LAIVG]P[WF][RKH] and triple [RKH] patterns. The most significant binding peptide, A21 (LPPWKHKTSGVA) was found in 4 separate screenings. The (110) geological aragonite sequences are highly enriched in prolines. Coincidently, peptides screened against the optical material LiNbO3 +Z show patterns similar to those found in the aragonite screenings. Other substrates that did not exhibit strong consensus include powdered LiNbO3, powdered BaTiO3, powdered PbTiO3, single crystal LiNbO3 –Z, and hydroxyapatite. A database and analysis program was written to catalog and evaluate the statistical significance of the many sequences. One peptide that was determined to be extremely significant in binding to aragonite, A20 (LPKWQERQMLSA), was modeled using umbrella sampling molecular dynamics techniques as well as analyzed by NMR. It was determined that there is a good probability that the peptide’s conformation is helical, but it is able to introconvert between α-helical, 3-10 helical and extended conformations fast enough that a stable secondary structure is not detectable by NMR. Engineered phage were constructed to display these significant peptides on the pVIII surface, increasing the expression level and the long range order in the hopes of building an aragonite nucleation surface. Hybrid organic-inorganic materials were grown on the phage resulting in a mixture of the three forms of CaCO3: calcite, vaterite, and aragonite. In addition, hybrid materials were grown on the optical waveguide material LiNbO3. Doubly engineered phage were shown to bind preferentially to the LiNbO3 +Z surface through the interaction of the A1 displayed peptide as well as nucleate semiconducting ZnS particles via the A7 peptide selected previously against ZnS.