Genetically Engineered Chimeric Silk-Silver Binding Proteins

Composite or hybrid materials are commonly found in Nature, formed through the concentration and subsequent nucleation of ions upon organic templates that are most often protein based. Examples include the deposition of calcium containing salts in bone, teeth and the inner ear and iron oxide structures in magnetotactic bacteria. Biological organisms use a limited number of metal ions, the principal ones being calcium and iron, with lesser amounts of strontium, and barium. The ability to utilize other ions to generate composites offers the possibility of new material properties. New materials incorporating silver would be useful in the context of antimicrobial functions. Therefore, in the present study, a new route to such functionalized biomaterials is reported. Genetically engineered fusion proteins are created by the incorporation of nucleotides corresponding to short silver binding peptides identified by a combinatorial biopanning process into the consensus sequence of silk from the spider, Nephila clavipes. The resulting chimeric silk-silver binding proteins nucleated Ag ions from a solution of silver nitrate while the silk protein provided a stable template material which could be processed into films, fibers, and three-dimensional scaffolds. The silk films inhibited microbial growth of both Gram-positive and Gram-negative micro-rganisms on agar plates and in liquid culture, thus highlighting the potential of these chimeric material systems as antimicrobial biomedical coatings.