Self-assembled monolayers from a designed combinatorial library of de novo β-sheet proteins

A variety of naturally occurring biomaterials owe their unusual structural and mechanical properties to layers of beta -sheet proteins laminated between layers of inorganic mineral. To explore the possibility of fabricating novel two-dimensional protein layers, we studied the self-assembly properties of de novo proteins from a designed combinatorial library. Each protein in the library has a distinct 63 amino acid sequence, yet they all share an identical binary pattern of polar and nonpolar residues, which was designed to favor the formation of six-stranded amphiphilic beta -sheets, Characterization of proteins isolated from the library demonstrates that (i) they self assemble into monolayers at an air/water interface; (ii) the monolayers are dominated by beta -sheet secondary structure, as shown by both circular dichroism and infrared spectroscopies; and (iii) the measured areas (500- 600 Angstrom (2)) Of individual protein molecules in the monolayers match those expected for proteins folded into amphiphilic beta -sheets, The finding that similar structures are formed by distinctly different protein sequences suggests that assembly into beta -sheet monolayers can be encoded by binary patterning of polar and nonpolar amino acids. Moreover, because the designed binary pattern is compatible with a wide variety of different sequences, it may be possible to fabricate beta -sheet monolayers by using combinations of side chains that are explicitly designed to favor particular applications of novel biomaterials.