Hierarchical self-assembly of designed 2 x 2-alpha-helix bundle proteins on Au(111) surfaces.
Self-assembled monolayers of biomolecules on atomically planar surfaces offer the prospect of complex combinations of controlled properties, e.g., for bioelectronics. We have prepared a novel hemi-4-alpha-helix bundle protein by attaching two alpha-helical peptides to a cyclo-dithiothreitol (cyclo-DTT) template. The protein was de novo designed to self-assemble in solution to form a 4-alpha-helix bundle, whereas the disulfide moiety enables the formation of a self-assembled monolayer on a Au(111) surface by opening of the disulfide, thus giving rise to a two-step self-assembly process. The 2 x 2-alpha-helix bundle protein and its template were studied by X-ray photo electron spectroscopy (XPS), electrochemical methods, and electrochemical in situ scanning tunneling microscopy (in situ STM). XPS showed that the cyclo-DTT opens on adsorption to a gold surface with the integrity of the 2 x 2-alpha-helix bundle proteins retained. The surface properties of the DTT and 2 x 2-alpha-helix bundle protein adlayer were characterized by interfacial capacitance and impedance techniques. Reductive desorption was used to determine the coverage of the adlayers, giving values of 65 and 16 muC cm(-2) for DTT and 2 x 2-helix, respectively. The 2 x 2-alpha-helix bundle protein adlayers were imaged by in situ STM. The images indicated a dense monolayer according with the voltammetric data. No long-range order could be detected, but two clearly distinct STM contrasts were assigned to 2 x 2-alpha-helix bundle protein molecules oriented in parallel and antiparallel conformations. The template molecule DTT alone forms highly ordered 30-40 nm domains, giving an adlayer density which agreed well with the coverage determined by voltammetry. This could be exploited in STM imaging of mixed DTT/2 x 2-alpha-helix bundle protein monolayers, with clearly distinct STM patterns of the two components.
Wackerbarth
Hainer
H
Department of Chemistry and Nano-DTU, Building 207, Technical University of Denmark, DK-2800 Lyngby, Denmark. hw@kemi.dtu.dk
Tofteng
A Pernille
AP
Jensen
Knud J
KJ
Chorkendorff
Ib
I
Ulstrup
Jens
J
D004563:Electrochemistry; D006046:Gold / Q000737:chemistry*; D015394:Molecular Structure; D010316:Particle Size; D017433:Protein Structure, Secondary; D011506:Proteins / Q000138:chemical synthesis / Q000737:chemistry*; D013499:Surface Properties
D011506:Proteins; D006046:Gold