Computational de novo design and characterization of a protein that selectively binds a highly hyperpolarizable abiological chromophore.
Journal Article (Journal Article)
This work reports the first example of a single-chain protein computationally designed to contain four α-helical segments and fold to form a four-helix bundle encapsulating a supramolecular abiological chromophore that possesses exceptional nonlinear optical properties. The 109-residue protein, designated SCRPZ-1, binds and disperses an insoluble hyperpolarizable chromophore, ruthenium(II) [5-(4'-ethynyl-(2,2';6',2″-terpyridinyl))-10,20-bis(phenyl)porphinato]zinc(II)-(2,2';6',2″-terpyridine)(2+) (RuPZn) in aqueous buffer solution at a 1:1 stoichiometry. A 1:1 binding stoichiometry of the holoprotein is supported by electronic absorption and circular dichroism spectra, as well as equilibrium analytical ultracentrifugation and size exclusion chromatography. SCRPZ-1 readily dimerizes at micromolar concentrations, and an empirical redesign of the protein exterior produced a stable monomeric protein, SCRPZ-2, that also displayed a 1:1 protein:cofactor stoichiometry. For both proteins in aqueous buffer, the encapsulated cofactor displays photophysical properties resembling those exhibited by the dilute RuPZn cofactor in organic solvent: femtosecond, nanosecond, and microsecond time scale pump-probe transient absorption spectroscopic data evince intensely absorbing holoprotein excited states having large spectral bandwidth that penetrate deep in the near-infrared energy regime; the holoprotein electronically excited triplet state exhibits a microsecond time scale lifetime characteristic of the RuPZn chromophore. Hyper-Rayleigh light scattering measurements carried out at an incident irradiation wavelength of 1340 nm for these holoproteins demonstrate an exceptional dynamic hyperpolarizabilty (β1340 = 3100 × 10(-30) esu). X-ray reflectivity measurements establish that this de novo-designed hyperpolarizable protein can be covalently attached with high surface density to a silicon surface without loss of the cofactor, indicating that these assemblies provide a new approach to bioinspired materials that have unique electro-optic functionality.
Full Text
Duke Authors
Cited Authors
- Fry, HC; Lehmann, A; Sinks, LE; Asselberghs, I; Tronin, A; Krishnan, V; Blasie, JK; Clays, K; DeGrado, WF; Saven, JG; Therien, MJ
Published Date
- September 2013
Published In
Volume / Issue
- 135 / 37
Start / End Page
- 13914 - 13926
PubMed ID
- 23931685
Pubmed Central ID
- PMC3787832
Electronic International Standard Serial Number (EISSN)
- 1520-5126
International Standard Serial Number (ISSN)
- 0002-7863
Digital Object Identifier (DOI)
- 10.1021/ja4067404
Language
- eng